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An Overview of Cryptography

1. INTRODUCTION

Does increased security provide comfort to paranoid people? Or does security provide some very basic protections that we are naive to believe that we don't need? During this time when the Internet provides essential communication between literally billions of people and is used as a tool for commerce, social interaction, and the exchange of an increasing amount of personal information, security has become a tremendously important issue for every user to deal with.

There are many aspects to security and many applications, ranging from secure commerce and payments to private communications and protecting health care information. One essential aspect for secure communications is that of cryptography. But it is important to note that while cryptography is necessary for secure communications, it is not by itself sufficient. The reader is advised, then, that the topics covered here only describe the first of many steps necessary for better security in any number of situations.

This paper has two major purposes. The first is to define some of the terms and concepts behind basic cryptographic methods, and to offer a way to compare the myriad cryptographic schemes in use today. The second is to provide some real examples of cryptography in use today. (See Section A.4 for some additional commentary on this)

DISCLAIMER: Several companies, products, and services are mentioned in this tutorial. Such mention is for example purposes only and, unless explicitly stated otherwise, should not be taken as a recommendation or endorsement by the author.

2. BASIC CONCEPTS OF CRYPTOGRAPHY

Cryptography &#; the science of secret writing &#; is an ancient art; the first documented use of cryptography in writing dates back to circa B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription. Some experts argue that cryptography appeared spontaneously sometime after writing was invented, with applications ranging from diplomatic missives to war-time battle plans. It is no surprise, then, that new forms of cryptography came soon after the widespread development of computer communications. In data and telecommunications, cryptography is necessary when communicating over any untrusted medium, which includes just about any network, particularly the Internet.

There are five primary functions of cryptography:

  1. Privacy/confidentiality: Ensuring that no one can read the message except the intended receiver.
  2. Authentication: The process of proving one's identity.
  3. Integrity: Assuring the receiver that the received message has not been altered in any way from the original.
  4. Non-repudiation: A mechanism to prove that the sender really sent this message.
  5. Key exchange: The method by which crypto keys are shared between sender and receiver.

In cryptography, we start with the unencrypted data, referred to as plaintext. Plaintext is encrypted into ciphertext, which will in turn (usually) be decrypted back into usable plaintext. The encryption and decryption is based upon the type of cryptography scheme being employed and some form of key. For those who like formulas, this process is sometimes written as:

C = Ek(P)
P = Dk(C)

      where P = plaintext, C = ciphertext, E = the encryption method, D = the decryption method, and k = the key.

Given this, there are other functions that might be supported by crypto and other terms that one might hear:

  • Forward Secrecy (aka Perfect Forward Secrecy): This feature protects past encrypted sessions from compromise even if the server holding the messages is compromised. This is accomplished by creating a different key for every session so that compromise of a single key does not threaten the entirely of the communications.
  • Perfect Security: A system that is unbreakable and where the ciphertext conveys no information about the plaintext or the key. To achieve perfect security, the key has to be at least as long as the plaintext, making analysis and even brute-force attacks impossible. One-time pads are an example of such a system.
  • Deniable Authentication (aka Message Repudiation): A method whereby participants in an exchange of messages can be assured in the authenticity of the messages but in such a way that senders can later plausibly deny their participation to a third-party.

In many of the descriptions below, two communicating parties will be referred to as Alice and Bob; this is the common nomenclature in the crypto field and literature to make it easier to identify the communicating parties. If there is a third and fourth party to the communication, they will be referred to as Carol and Dave, respectively. A malicious party is referred to as Mallory, an eavesdropper as Eve, and a trusted third party as Trent.

Finally, cryptography is most closely associated with the development and creation of the mathematical algorithms used to encrypt and decrypt messages, whereas cryptanalysis is the science of analyzing and breaking encryption schemes. Cryptology is the umbrella term referring to the broad study of secret writing, and encompasses both cryptography and cryptanalysis.

3. TYPES OF CRYPTOGRAPHIC ALGORITHMS

There are several ways of classifying cryptographic algorithms. For purposes of this paper, they will be categorized based on the number of keys that are employed for encryption and decryption, and further defined by their application and use. The three types of algorithms that will be discussed are (Figure 1):

  • Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption; also called symmetric encryption. Primarily used for privacy and confidentiality.
  • Public Key Cryptography (PKC): Uses one key for encryption and another for decryption; also called asymmetric encryption. Primarily used for authentication, non-repudiation, and key exchange.
  • Hash Functions: Uses a mathematical transformation to irreversibly "encrypt" information, providing a digital fingerprint. Primarily used for message integrity.

FIGURE 1: Three types of cryptography: secret key, public key, and hash function.

Secret Key Cryptography

Secret key cryptography methods employ a single key for both encryption and decryption. As shown in Figure 1A, the sender uses the key to encrypt the plaintext and sends the ciphertext to the receiver. The receiver applies the same key to decrypt the message and recover the plaintext. Because a single key is used for both functions, secret key cryptography is also called symmetric encryption.

With this form of cryptography, it is obvious that the key must be known to both the sender and the receiver; that, in fact, is the secret. The biggest difficulty with this approach, of course, is the distribution of the key (more on that later in the discussion of public key cryptography).

Secret key cryptography schemes are generally categorized as being either stream ciphers or block ciphers.

A) Self-synchronizing stream cipher. (From Schneier, , Figure )

B) Synchronous stream cipher. (From Schneier, , Figure )

FIGURE 2: Types of stream ciphers.

Stream ciphers operate on a single bit (byte or computer word) at a time and implement some form of feedback mechanism so that the key is constantly changing. Stream ciphers come in several flavors but two are worth mentioning here (Figure 2). Self-synchronizing stream ciphers calculate each bit in the keystream as a function of the previous n bits in the keystream. It is termed "self-synchronizing" because the decryption process can stay synchronized with the encryption process merely by knowing how far into the n-bit keystream it is. One problem is error propagation; a garbled bit in transmission will result in n garbled bits at the receiving side. Synchronous stream ciphers generate the keystream in a fashion independent of the message stream but by using the same keystream generation function at sender and receiver. While stream ciphers do not propagate transmission errors, they are, by their nature, periodic so that the keystream will eventually repeat.

FIGURE 3: Feistel cipher. (Source: Wikimedia Commons)

A block cipher is so-called because the scheme encrypts one fixed-size block of data at a time. In a block cipher, a given plaintext block will always encrypt to the same ciphertext when using the same key (i.e., it is deterministic) whereas the same plaintext will encrypt to different ciphertext in a stream cipher. The most common construct for block encryption algorithms is the Feistel cipher, named for cryptographer Horst Feistel (IBM). As shown in Figure 3, a Feistel cipher combines elements of substitution, permutation (transposition), and key expansion; these features create a large amount of "confusion and diffusion" (per Claude Shannon) in the cipher. One advantage of the Feistel design is that the encryption and decryption stages are similar, sometimes identical, requiring only a reversal of the key operation, thus dramatically reducing the size of the code or circuitry necessary to implement the cipher in software or hardware, respectively. One of Feistel's early papers describing this operation is "Cryptography and Computer Privacy" (Scientific American, May , (5), ).

Block ciphers can operate in one of several modes; the following are the most important:

  • Electronic Codebook (ECB) mode is the simplest, most obvious application: the secret key is used to encrypt the plaintext block to form a ciphertext block. Two identical plaintext blocks, then, will always generate the same ciphertext block. ECB is susceptible to a variety of brute-force attacks (because of the fact that the same plaintext block will always encrypt to the same ciphertext), as well as deletion and insertion attacks. In addition, a single bit error in the transmission of the ciphertext results in an error in the entire block of decrypted plaintext.
  • Cipher Block Chaining (CBC) mode adds a feedback mechanism to the encryption scheme; the plaintext is exclusively-ORed (XORed) with the previous ciphertext block prior to encryption so that two identical plaintext blocks will encrypt differently. While CBC protects against many brute-force, deletion, and insertion attacks, a single bit error in the ciphertext yields an entire block error in the decrypted plaintext block and a bit error in the next decrypted plaintext block.
  • Cipher Feedback (CFB) mode is a block cipher implementation as a self-synchronizing stream cipher. CFB mode allows data to be encrypted in units smaller than the block size, which might be useful in some applications such as encrypting interactive terminal input. If we were using one-byte CFB mode, for example, each incoming character is placed into a shift register the same size as the block, encrypted, and the block transmitted. At the receiving side, the ciphertext is decrypted and the extra bits in the block (i.e., everything above and beyond the one byte) are discarded. CFB mode generates a keystream based upon the previous ciphertext (the initial key comes from an Initialization Vector [IV]). In this mode, a single bit error in the ciphertext affects both this block and the following one.
  • Output Feedback (OFB) mode is a block cipher implementation conceptually similar to a synchronous stream cipher. OFB prevents the same plaintext block from generating the same ciphertext block by using an internal feedback mechanism that generates the keystream independently of both the plaintext and ciphertext bitstreams. In OFB, a single bit error in ciphertext yields a single bit error in the decrypted plaintext.
  • Counter (CTR) mode is a relatively modern addition to block ciphers. Like CFB and OFB, CTR mode operates on the blocks as in a stream cipher; like ECB, CTR mode operates on the blocks independently. Unlike ECB, however, CTR uses different key inputs to different blocks so that two identical blocks of plaintext will not result in the same ciphertext. Finally, each block of ciphertext has specific location within the encrypted message. CTR mode, then, allows blocks to be processed in parallel &#; thus offering performance advantages when parallel processing and multiple processors are available &#; but is not susceptible to ECB's brute-force, deletion, and insertion attacks.

A good overview of these different modes can be found at CRYPTO-IT.

Secret key cryptography algorithms in use today &#; or, at least, important today even if not in use &#; include:

  • Data Encryption Standard (DES): One of the most well-known and well-studied SKC schemes, DES was designed by IBM in the s and adopted by the National Bureau of Standards (NBS) [now the National Institute of Standards and Technology (NIST)] in for commercial and unclassified government applications. DES is a Feistel block-cipher employing a bit key that operates on bit blocks. DES has a complex set of rules and transformations that were designed specifically to yield fast hardware implementations and slow software implementations, although this latter point is not significant today since the speed of computer processors is several orders of magnitude faster today than even twenty years ago. DES was based somewhat on an earlier cipher from Feistel called Lucifer which, some sources report, had a bit key. This was rejected, partially in order to fit the algorithm onto a single chip and partially because of the National Security Agency (NSA). The NSA also proposed a number of tweaks to DES that many thought were introduced in order to weaken the cipher; analysis in the s, however, showed that the NSA suggestions actually strengthened DES, including the removal of a mathematical back door by a change to the design of the S-box (see "The Legacy of DES" by Bruce Schneier []). In April , the NSA declassified a fascinating historical paper titled "NSA Comes Out of the Closet: The Debate over Public Cryptography in the Inman Era" that appeared in Cryptologic Quarterly, Spring

    DES was defined in American National Standard X and three Federal Information Processing Standards (FIPS), all withdrawn in

    • FIPS PUB DES (Archived file)
    • FIPS PUB Guidelines for Implementing and Using the NBS Data Encryption Standard
    • FIPS PUB DES Modes of Operation

    Information about vulnerabilities of DES can be obtained from the Electronic Frontier Foundation.

    Two important variants that strengthen DES are:

    • Triple-DES (3DES): A variant of DES that employs up to three bit keys and makes three encryption/decryption passes over the block; 3DES is also described in FIPS PUB and was an interim replacement to DES in the lates and earlys.

    • DESX: A variant devised by Ron Rivest. By combining 64 additional key bits to the plaintext prior to encryption, effectively increases the keylength to bits.

    More detail about DES, 3DES, and DESX can be found below in Section

  • Advanced Encryption Standard (AES): In , NIST initiated a very public, /2 year process to develop a new secure cryptosystem for U.S. government applications (as opposed to the very closed process in the adoption of DES 25 years earlier). The result, the Advanced Encryption Standard, became the official successor to DES in December AES uses an SKC scheme called Rijndael, a block cipher designed by Belgian cryptographers Joan Daemen and Vincent Rijmen. The algorithm can use a variable block length and key length; the latest specification allowed any combination of keys lengths of , , or bits and blocks of length , , or bits. NIST initially selected Rijndael in October and formal adoption as the AES standard came in December FIPS PUB describes a bit block cipher employing a , , or bit key. AES is also part of the NESSIE approved suite of protocols. (See also the entries for CRYPTEC and NESSIE Projects in Table 3.)

    The AES process and Rijndael algorithm are described in more detail below in Section

  • CAST/ CAST (aka CAST5), described in Request for Comments (RFC) , is a DES-like substitution-permutation crypto algorithm, employing a bit key operating on a bit block. CAST (aka CAST6), described in RFC , is an extension of CAST, using a bit block size and a variable length (, , , , or bit) key. CAST is named for its developers, Carlisle Adams and Stafford Tavares, and is available internationally. CAST was one of the Round 1 algorithms in the AES process.

  • International Data Encryption Algorithm (IDEA): Secret-key cryptosystem written by Xuejia Lai and James Massey, in and patented by Ascom; a bit SKC block cipher using a bit key.

  • Rivest Ciphers (aka Ron's Code): Named for Ron Rivest, a series of SKC algorithms.

    • RC1: Designed on paper but never implemented.

    • RC2: A bit block cipher using variable-sized keys designed to replace DES. It's code has not been made public although many companies have licensed RC2 for use in their products. Described in RFC

    • RC3: Found to be breakable during development.

    • RC4: A stream cipher using variable-sized keys; it is widely used in commercial cryptography products. An update to RC4, called Spritz (see also this article), was designed by Rivest and Jacob Schuldt. More detail about RC4 (and a little about Spritz) can be found below in Section

    • RC5: A block-cipher supporting a variety of block sizes (32, 64, or bits), key sizes, and number of encryption passes over the data. Described in RFC

    • RC6: A bit block cipher based upon, and an improvement over, RC5; RC6 was one of the AES Round 2 algorithms.

  • Blowfish: A symmetric bit block cipher invented by Bruce Schneier; optimized for bit processors with large data caches, it is significantly faster than DES on a Pentium/PowerPC-class machine. Key lengths can vary from 32 to bits in length. Blowfish, available freely and intended as a substitute for DES or IDEA, is in use in a large number of products.

  • Twofish: A bit block cipher using , , or bit keys. Designed to be highly secure and highly flexible, well-suited for large microprocessors, 8-bit smart card microprocessors, and dedicated hardware. Designed by a team led by Bruce Schneier and was one of the Round 2 algorithms in the AES process.

  • Threefish: A large block cipher, supporting , , and bit blocks and a key size that matches the block size; by design, the block/key size can grow in increments of bits. Threefish only uses XOR operations, addition, and rotations of bit words; the design philosophy is that an algorithm employing many computationally simple rounds is more secure than one employing highly complex &#; albeit fewer &#; rounds. The specification for Threefish is part of the Skein Hash Function Family documentation.

  • Anubis: Anubis is a block cipher, co-designed by Vincent Rijmen who was one of the designers of Rijndael. Anubis is a block cipher, performing substitution-permutation operations on bit blocks and employing keys of length to bits (in bit increments). Anubis works very much like Rijndael. Although submitted to the NESSIE project, it did not make the final cut for inclusion.

  • ARIA: A bit block cipher employing , , and bit keys to encrypt bit blocks in 12, 14, and 16 rounds, depending on the key size. Developed by large group of researchers from academic institutions, research institutes, and federal agencies in South Korea in , and subsequently named a national standard. Described in RFC

  • Camellia: A secret-key, block-cipher crypto algorithm developed jointly by Nippon Telegraph and Telephone (NTT) Corp. and Mitsubishi Electric Corporation (MEC) in Camellia has some characteristics in common with AES: a bit block size, support for , , and bit key lengths, and suitability for both software and hardware implementations on common bit processors as well as 8-bit processors (e.g., smart cards, cryptographic hardware, and embedded systems). Also described in RFC Camellia's application in IPsec is described in RFC and application in OpenPGP in RFC Camellia is part of the NESSIE suite of protocols.

  • CLEFIA: Described in RFC , CLEFIA is a bit block cipher employing key lengths of , , and bits (which is compatible with AES). The CLEFIA algorithm was first published in by Sony Corporation. CLEFIA is one of the new-generation lightweight blockcipher algorithms designed after AES, offering high performance in software and hardware as well as a lightweight implementation in hardware.

  • FFX-A2 and FFX-A10: FFX (Format-preserving, Feistel-based encryption) is a type of Format Preserving Encryption (FPE) scheme that is designed so that the ciphertext has the same format as the plaintext. FPE schemes are used for such purposes as encrypting social security numbers, credit card numbers, limited size protocol traffic, etc.; this means that an encrypted social security number, for example, would still be a nine-digit string. FFX can theoretically encrypt strings of arbitrary length, although it is intended for message sizes smaller than that of AES (2 points). The FFX version specification describes FFX-A2 and FFX-A10, which are intended for bit binary strings or digit decimal strings.

  • GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile) encryption: GSM mobile phone systems use several stream ciphers for over-the-air communication privacy. A5/1 was developed in for use in Europe and the U.S. A5/2, developed in , is a weaker algorithm and intended for use outside of Europe and the U.S. Significant flaws were found in both ciphers after the "secret" specifications were leaked in , however, and A5/2 has been withdrawn from use. The newest version, A5/3, employs the KASUMI block cipher. NOTE: Unfortunately, although A5/1 has been repeatedly "broken" (e.g., see "Secret code protecting cellphone calls set loose" [] and "Cellphone snooping now easier and cheaper than ever" []), this encryption scheme remains in widespread use, even in 3G and 4G mobile phone networks. Use of this scheme is reportedly one of the reasons that the National Security Agency (NSA) can easily decode voice and data calls over mobile phone networks.

  • GPRS (General Packet Radio Service) encryption: GSM mobile phone systems use GPRS for data applications, and GPRS uses a number of encryption methods, offering different levels of data protection. GEA/0 offers no encryption at all. GEA/1 and GEA/2 are proprietary stream ciphers, employing a bit key and a bit or bit state, respectively. GEA/1 and GEA/2 are most widely used by network service providers today although both have been reportedly broken. GEA/3 is a bit block cipher employing a bit key that is used by some carriers; GEA/4 is a bit clock cipher with a bit key, but is not yet deployed.

  • KASUMI: A block cipher using a bit key that is part of the Third-Generation Partnership Project (3gpp), formerly known as the Universal Mobile Telecommunications System (UMTS). KASUMI is the intended confidentiality and integrity algorithm for both message content and signaling data for emerging mobile communications systems.

  • KCipher Described in RFC , KCipher-2 is a stream cipher with a bit key and a bit initialization vector. Using simple arithmetic operations, the algorithms offers fast encryption and decryption by use of efficient implementations. KCipher-2 has been used for industrial applications, especially for mobile health monitoring and diagnostic services in Japan.

  • KHAZAD:KHAZAD is a so-called legacy block cipher, operating on bit blocks à la older block ciphers such as DES and IDEA. KHAZAD uses eight rounds of substitution and permutation, with a bit key.

  • KLEIN: Designed in , KLEIN is a lightweight, bit block cipher supporting , and bit keys. KLEIN is designed for highly resource constrained devices such as wireless sensors and RFID tags.

  • Light Encryption Device (LED): Designed in , LED is a lightweight, bit block cipher supporting and bit keys. LED is designed for RFID tags, sensor networks, and other applications with devices constrained by memory or compute power.

  • MARS:MARS is a block cipher developed by IBM and was one of the five finalists in the AES development process. MARS employs bit blocks and a variable key length from to bits. The MARS document stresses the ability of the algorithm's design for high speed, high security, and the ability to efficiently and effectively implement the scheme on a wide range of computing devices.

  • MISTY1: Developed at Mitsubishi Electric Corp., a block cipher using a bit key and bit blocks, and a variable number of rounds. Designed for hardware and software implementations, and is resistant to differential and linear cryptanalysis. Described in RFC , MISTY1 is part of the NESSIE suite.

  • Salsa and ChaCha: Salsa20 is a stream cipher proposed for the eSTREAM project by Daniel Bernstein. Salsa20 uses a pseudorandom function based on bit (whole word) addition, bitwise addition (XOR), and rotation operations, aka add-rotate-xor (ARX) operations. Salsa20 uses a bit key although a bit key variant also exists. In , Bernstein published ChaCha, a new family of ciphers related to Salsa ChaCha20, originally defined in RFC (now obsoleted), is employed (with the Poly authenticator) in Internet Engineering Task Force (IETF) protocols, most notably for IPsec and Internet Key Exchange (IKE), per RFC , and Transaction Layer Security (TLS), per RFC In , Google adopted ChaCha20/Poly for use in OpenSSL, and they are also a part of OpenSSH. RFC replaces RFC , and provides an implementation guide for both the ChaCha20 cipher and Poly message authentication code, as well as the combined CHACHAPOLY Authenticated-Encryption with Associated-Data (AEAD) algorithm.

  • Secure and Fast Encryption Routine (SAFER): A series of block ciphers designed by James Massey for implementation in software and employing a bit block. SAFER K, published in , used a bit key and SAFER K, published in , employed a bit key. After weaknesses were found, new versions were released called SAFER SK, SK, and SK, using , , and bit keys, respectively. SAFER+ () used a bit block and was an unsuccessful candidate for the AES project; SAFER++ () was submitted to the NESSIE project.

  • SEED: A block cipher using bit blocks and bit keys. Developed by the Korea Information Security Agency (KISA) and adopted as a national standard encryption algorithm in South Korea. Also described in RFC

  • Serpent:Serpent is another of the AES finalist algorithms. Serpent supports , , or bit keys and a block size of bits, and is a round substitution–permutation network operating on a block of four bit words. The Serpent developers opted for a high security margin in the design of the algorithm; they determined that 16 rounds would be sufficient against known attacks but require 32 rounds in an attempt to future-proof the algorithm.

  • SHACAL: SHACAL is a pair of block ciphers based upon the Secure Hash Algorithm (SHA) and the fact that SHA is, at heart, a compression algorithm. As a hash function, SHA repeatedly calls on a compression scheme to alter the state of the data blocks. While SHA (like other hash functions) is irreversible, the compression function can be used for encryption by maintaining appropriate state information. SHACAL-1 is based upon SHA-1 and uses a bit block size while SHACAL-2 is based upon SHA and employs a bit block size; both support key sizes from to bits. SHACAL-2 is one of the NESSIE block ciphers.

  • Simon and Speck: Simon and Speck are a pair of lightweight block ciphers proposed by the NSA in , designed for highly constrained software or hardware environments. (E.g., per the specification, AES requires gate equivalents and these ciphers require less than ) While both cipher families perform well in both hardware and software, Simon has been optimized for high performance on hardware devices and Speck for performance in software. Both are Feistel ciphers and support ten combinations of block and key size:

  • Skipjack: SKC scheme proposed, along with the Clipper chip, as part of the never-implemented Capstone project. Although the details of the algorithm were never made public, Skipjack was a block cipher using an bit key and 32 iteration cycles per bit block. Capstone, proposed by NIST and the NSA as a standard for public and government use, met with great resistance by the crypto community largely because the design of Skipjack was classified (coupled with the key escrow requirement of the Clipper chip).

  • SM4: Formerly called SMS4, SM4 is a bit block cipher using bit keys and 32 rounds to process a block. Declassified in , SM4 is used in the Chinese National Standard for Wireless Local Area Network (LAN) Authentication and Privacy Infrastructure (WAPI). SM4 had been a proposed cipher for the Institute of Electrical and Electronics Engineers (IEEE) i standard on security mechanisms for wireless LANs, but has yet to be accepted by the IEEE or International Organization for Standardization (ISO). SM4 is described in SMS4 Encryption Algorithm for Wireless Networks (translated by Whitfield Diffie and George Ledin, ) and at the SM4 (cipher) page. SM4 is issued by the Chinese State Cryptographic Authority as GM/T SM4 ().

  • Tiny Encryption Algorithm (TEA): A family of block ciphers developed by Roger Needham and David Wheeler. TEA was originally developed in , and employed a bit key, bit block, and 64 rounds of operation. To correct certain weaknesses in TEA, eXtended TEA (XTEA), aka Block TEA, was released in To correct weaknesses in XTEA and add versatility, Corrected Block TEA (XXTEA) was published in XXTEA also uses a bit key, but block size can be any multiple of bit words (with a minimum block size of 64 bits, or two words) and the number of rounds is a function of the block size (~52+6*words), as shown in Table 1.

  • Block Size
    2n
    Key Size
    mn
    Word Size
    n
    Key Words
    m
    Rounds
    T
    326416432
    4872
    96
    243
    4
    36
    36
    6496
    323
    4
    42
    44
    9696
    482
    3
    52
    54


    642
    3
    4
    68
    69
    72
  • TWINE: Designed by engineers at NEC in , TWINE is a lightweight, bit block cipher supporting and bit keys. TWINE's design goals included maintaining a small footprint in a hardware implementation (i.e., fewer than 2, gate equivalents) and small memory consumption in a software implementation.

Although not an SKC scheme, check out Section about Shamir's Secret Sharing (SSS).

There are several other references that describe interesting algorithms and even SKC codes dating back decades. Two that leap to mind are the Crypto Museum's Crypto List and John J.G. Savard's (albeit old) A Cryptographic Compendium page.

Public Key Cryptography

Public key cryptography has been said to be the most significant new development in cryptography in the last years. Modern PKC was first described publicly by Stanford University professor Martin Hellman and graduate student Whitfield Diffie in Their paper described a two-key crypto system in which two parties could engage in a secure communication over a non-secure communications channel without having to share a secret key.

PKC depends upon the existence of so-called one-way functions, or mathematical functions that are easy to compute whereas their inverse function is relatively difficult to compute. Let me give you two simple examples:

  1. Multiplication vs. factorization: Suppose you have two prime numbers, 3 and 7, and you need to calculate the product; it should take almost no time to calculate that value, which is Now suppose, instead, that you have a number that is a product of two primes, 21, and you need to determine those prime factors. You will eventually come up with the solution but whereas calculating the product took milliseconds, factoring will take longer. The problem becomes much harder if we start with primes that have, say, digits or so, because the product will have ~ digits.
  2. Exponentiation vs. logarithms: Suppose you take the number 3 to the 6th power; again, it is relatively easy to calculate 36 =  But if you start with the number and need to determine the two integers, x and y so that logx  = y, it will take longer to find the two values.

While the examples above are trivial, they do represent two of the functional pairs that are used with PKC; namely, the ease of multiplication and exponentiation versus the relative difficulty of factoring and calculating logarithms, respectively. The mathematical "trick" in PKC is to find a trap door in the one-way function so that the inverse calculation becomes easy given knowledge of some item of information.

Generic PKC employs two keys that are mathematically related although knowledge of one key does not allow someone to easily determine the other key. One key is used to encrypt the plaintext and the other key is used to decrypt the ciphertext. The important point here is that it does not matter which key is applied first, but that both keys are required for the process to work (Figure 1B). Because a pair of keys are required, this approach is also called asymmetric cryptography.

In PKC, one of the keys is designated the public key and may be advertised as widely as the owner wants. The other key is designated the private key and is never revealed to another party. It is straight-forward to send messages under this scheme. Suppose Alice wants to send Bob a message. Alice encrypts some information using Bob's public key; Bob decrypts the ciphertext using his private key. This method could be also used to prove who sent a message; Alice, for example, could encrypt some plaintext with her private key; when Bob decrypts using Alice's public key, he knows that Alice sent the message (authentication) and Alice cannot deny having sent the message (non-repudiation).

Public key cryptography algorithms that are in use today for key exchange or digital signatures include:

  • RSA: The first, and still most common, PKC implementation, named for the three MIT mathematicians who developed it &#; Ronald Rivest, Adi Shamir, and Leonard Adleman. RSA today is used in hundreds of software products and can be used for key exchange, digital signatures, or encryption of small blocks of data. RSA uses a variable size encryption block and a variable size key. The key-pair is derived from a very large number, n, that is the product of two prime numbers chosen according to special rules; these primes may be or more digits in length each, yielding an n with roughly twice as many digits as the prime factors. The public key information includes n and a derivative of one of the factors of n; an attacker cannot determine the prime factors of n (and, therefore, the private key) from this information alone and that is what makes the RSA algorithm so secure. (Some descriptions of PKC erroneously state that RSA's safety is due to the difficulty in factoring large prime numbers. In fact, large prime numbers, like small prime numbers, only have two factors!) The ability for computers to factor large numbers, and therefore attack schemes such as RSA, is rapidly improving and systems today can find the prime factors of numbers with more than digits. Nevertheless, if a large number is created from two prime factors that are roughly the same size, there is no known factorization algorithm that will solve the problem in a reasonable amount of time; a test to factor a digit number took years and over 50 years of compute time. In , Kleinjung et al. reported that factoring a bit (digit) RSA modulus utilizing hundreds of systems took two years and they estimated that a bit RSA modulus would take about a thousand times as long. Even so, they suggested that bit RSA be phased out by (See the Wikipedia article on integer factorization.) Regardless, one presumed protection of RSA is that users can easily increase the key size to always stay ahead of the computer processing curve. As an aside, the patent for RSA expired in September which does not appear to have affected RSA's popularity one way or the other. A detailed example of RSA is presented below in Section

  • Diffie-Hellman: After the RSA algorithm was published, Diffie and Hellman came up with their own algorithm. Diffie-Hellman is used for secret-key key exchange only, and not for authentication or digital signatures. More detail about Diffie-Hellman can be found below in Section

  • Digital Signature Algorithm (DSA): The algorithm specified in NIST's Digital Signature Standard (DSS), provides digital signature capability for the authentication of messages. Described in FIPS PUB

  • ElGamal: Designed by Taher Elgamal, ElGamal is a PKC system similar to Diffie-Hellman and used for key exchange. ElGamal is used in some later version of Pretty Good Privacy (PGP) as well as GNU Privacy Guard (GPG) and other cryptosystems.

  • Elliptic Curve Cryptography (ECC): A PKC algorithm based upon elliptic curves. ECC can offer levels of security with small keys comparable to RSA and other PKC methods. It was designed for devices with limited compute power and/or memory, such as smartcards and PDAs. More detail about ECC can be found below in Section Other references include the Elliptic Curve Cryptography page and the Online ECC Tutorial page, both from Certicom. See also RFC for a review of fundamental ECC algorithms and The Elliptic Curve Digital Signature Algorithm (ECDSA) for details about the use of ECC for digital signatures.

  • Identity-Based Encryption (IBE): IBE is a novel scheme first proposed by Adi Shamir in It is a PKC-based key authentication system where the public key can be derived from some unique information based upon the user's identity, allowing two users to exchange encrypted messages without having an a priori relationship. In , Dan Boneh (Stanford) and Matt Franklin (U.C., Davis) developed a practical implementation of IBE based on elliptic curves and a mathematical construct called the Weil Pairing. In that year, Clifford Cocks (GCHQ) also described another IBE solution based on quadratic residues in composite groups. RFC Identity-Based Cryptography Standard (IBCS) #1 describes an implementation of IBE using Boneh-Franklin (BF) and Boneh-Boyen (BB1) Identity-based Encryption. More detail about Identity-Based Encryption can be found below in Section

  • Public Key Cryptography Standards (PKCS): A set of interoperable standards and guidelines for public key cryptography, designed by RSA Data Security Inc. (These documents are no longer easily available; all links in this section are from storycall.us.)

  • Cramer-Shoup: A public key cryptosystem proposed by R. Cramer and V. Shoup of IBM in

  • Key Exchange Algorithm (KEA): A variation on Diffie-Hellman; proposed as the key exchange method for the NIST/NSA Capstone project.

  • LUC: A public key cryptosystem designed by P.J. Smith and based on Lucas sequences. Can be used for encryption and signatures, using integer factoring.

  • McEliece: A public key cryptosystem based on algebraic coding theory.

For additional information on PKC algorithms, see "Public Key Encryption" (Chapter 8) in Handbook of Applied Cryptography, by A. Menezes, P. van Oorschot, and S. Vanstone (CRC Press, ).


A digression: Who invented PKC? I tried to be careful in the first paragraph of this section to state that Diffie and Hellman "first described publicly" a PKC scheme. Although I have categorized PKC as a two-key system, that has been merely for convenience; the real criteria for a PKC scheme is that it allows two parties to exchange a secret even though the communication with the shared secret might be overheard. There seems to be no question that Diffie and Hellman were first to publish; their method is described in the classic paper, "New Directions in Cryptography," published in the November issue of IEEE Transactions on Information Theory (IT(6), ). As shown in Section , Diffie-Hellman uses the idea that finding logarithms is relatively harder than performing exponentiation. And, indeed, it is the precursor to modern PKC which does employ two keys. Rivest, Shamir, and Adleman described an implementation that extended this idea in their paper, "A Method for Obtaining Digital Signatures and Public Key Cryptosystems," published in the February issue of the Communications of the ACM (CACM), (21(2), ). Their method, of course, is based upon the relative ease of finding the product of two large prime numbers compared to finding the prime factors of a large number.

Diffie and Hellman (and other sources) credit Ralph Merkle with first describing a public key distribution system that allows two parties to share a secret, although it was not a two-key system, per se. A Merkle Puzzle works where Alice creates a large number of encrypted keys, sends them all to Bob so that Bob chooses one at random and then lets Alice know which he has selected. An eavesdropper (Eve) will see all of the keys but can't learn which key Bob has selected (because he has encrypted the response with the chosen key). In this case, Eve's effort to break in is the square of the effort of Bob to choose a key. While this difference may be small it is often sufficient. Merkle apparently took a computer science course at UC Berkeley in and described his method, but had difficulty making people understand it; frustrated, he dropped the course. Meanwhile, he submitted the paper "Secure Communication Over Insecure Channels," which was published in the CACM in April ; Rivest et al.'s paper even makes reference to it. Merkle's method certainly wasn't published first, but he is often credited to have had the idea first.

An interesting question, maybe, but who really knows? For some time, it was a quiet secret that a team at the UK's Government Communications Headquarters (GCHQ) had first developed PKC in the early s. Because of the nature of the work, GCHQ kept the original memos classified. In , however, the GCHQ changed their posture when they realized that there was nothing to gain by continued silence. Documents show that a GCHQ mathematician named James Ellis started research into the key distribution problem in and that by , James Ellis, Clifford Cocks, and Malcolm Williamson had worked out all of the fundamental details of PKC, yet couldn't talk about their work. (They were, of course, barred from challenging the RSA patent!) By , Ellis, Cocks, and Williamson began to get their due credit in a break-through article in WIRED Magazine. And the National Security Agency (NSA) claims to have knowledge of this type of algorithm as early as For some additional insight on who knew what when, see Steve Bellovin's "The Prehistory of Public Key Cryptography."


Hash Functions

Hash functions, also called message digests and one-way encryption, are algorithms that, in essence, use no key (Figure 1C). Instead, a fixed-length hash value is computed based upon the plaintext that makes it impossible for either the contents or length of the plaintext to be recovered. Hash algorithms are typically used to provide a digital fingerprint of a file's contents, often used to ensure that the file has not been altered by an intruder or virus. Hash functions are also commonly employed by many operating systems to encrypt passwords. Hash functions, then, provide a mechanism to ensure the integrity of a file.

Hash functions are also designed so that small changes in the input produce significant differences in the hash value, for example:

Hash string 1: The quick brown fox jumps over the lazy dog
Hash string 2: The quick brown fox jumps over the lazy dog.

MD5 [hash string 1] = 37c4b87edffc5dff5acee7ee09
MD5 [hash string 2] = 0dcde94cfe1d2ae0c8e

SHA1 [hash string 1] = beb5c3c5c1d9bcb2e7cdd76b
SHA1 [hash string 2] = 9c04cde9b11f70cacdce4b

RIPEMD [hash string 1] = eefdda9e2cff
RIPEMD [hash string 2] = 99bacdbe25bbee


Let me reiterate that hashes are one-way encryption. You cannot take a hash and "decrypt" it to find the original string that created it, despite the many web sites that claim or suggest otherwise, such as CrackStation, storycall.us, MD5 Online, md5thiscracker, OnlineHashCrack, and RainbowCrack.

Note that these sites search databases and/or use rainbow tables to find a suitable string that produces the hash in question but one can't definitively guarantee what string originally produced the hash. This is an important distinction. Suppose that you want to crack someone's password, where the hash of the password is stored on the server. Indeed, all you then need is a string that produces the correct hash and you're in! However, you cannot prove that you have discovered the user's password, only a "duplicate key."


Hash algorithms in common use today include:

  • Message Digest (MD) algorithms: A series of byte-oriented algorithms that produce a bit hash value from an arbitrary-length message.

    • MD2 (RFC ): Designed for systems with limited memory, such as smart cards. (MD2 has been relegated to historical status, per RFC )

    • MD4 (RFC ): Developed by Rivest, similar to MD2 but designed specifically for fast processing in software. (MD4 has been relegated to historical status, per RFC )

    • MD5 (RFC ): Also developed by Rivest after potential weaknesses were reported in MD4; this scheme is similar to MD4 but is slower because more manipulation is made to the original data. MD5 has been implemented in a large number of products although several weaknesses in the algorithm were demonstrated by German cryptographer Hans Dobbertin in ("Cryptanalysis of MD5 Compress"). (Updated security considerations for MD5 can be found in RFC )

  • Secure Hash Algorithm (SHA): Algorithm for NIST's Secure Hash Standard (SHS), described in FIPS PUB The status of NIST hash algorithms can be found on their "Policy on Hash Functions" page.

    • SHA-1 produces a bit hash value and was originally published as FIPS PUB and RFC SHA-1 was deprecated by NIST as of the end of although it is still widely used.

    • SHA-2, originally described in FIPS PUB and eventually replaced by FIPS PUB (and FIPS PUB ), comprises five algorithms in the SHS: SHA-1 plus SHA, SHA, SHA, and SHA which can produce hash values that are , , , or bits in length, respectively. SHA-2 recommends use of SHA-1, SHA, and SHA for messages less than 264 bits in length, and employs a bit block size; SHA and SHA are recommended for messages less than 2 bits in length, and employs a 1, bit block size. FIPS PUB also introduces the concept of a truncated hash in SHA/t, a generic name referring to a hash value based upon the SHA algorithm that has been truncated to t bits; SHA/ and SHA/ are specifically described. SHA, , , and are also described in RFC

    • SHA-3 is the current SHS algorithm. Although there had not been any successful attacks on SHA-2, NIST decided that having an alternative to SHA-2 using a different algorithm would be prudent. In , they launched a SHA-3 Competition to find that alternative; a list of submissions can be found at The SHA-3 Zoo. In , NIST announced that after reviewing 64 submissions, the winner was Keccak (pronounced "catch-ack"), a family of hash algorithms based on sponge functions. The NIST version can support hash output sizes of and bits.

  • RIPEMD: A series of message digests that initially came from the RIPE (RACE Integrity Primitives Evaluation) project. RIPEMD was designed by Hans Dobbertin, Antoon Bosselaers, and Bart Preneel, and optimized for bit processors to replace the then-current bit hash functions. Other versions include RIPEMD, RIPEMD, and RIPEMD

  • eD2k: Named for the EDonkey Network (eD2K), the eD2k hash is a root hash of an MD4 hash list of a given file. A root hash is used on peer-to-peer file transfer networks, where a file is broken into chunks; each chunk has its own MD4 hash associated with it and the server maintains a file that contains the hash list of all of the chunks. The root hash is the hash of the hash list file.

  • HAVAL (HAsh of VAriable Length): Designed by Y. Zheng, J. Pieprzyk and J. Seberry, a hash algorithm with many levels of security. HAVAL can create hash values that are , , , , or bits in length. More details can be found in "HAVAL - A one-way hashing algorithm with variable length output" by Zheng, Pieprzyk, and Seberry (AUSCRYPT '92).

  • The Skein Hash Function Family: The Skein Hash Function Family was proposed to NIST in their hash function competition. Skein is fast due to using just a few simple computational primitives, secure, and very flexible &#; per the specification, it can be used as a straight-forward hash, MAC, HMAC, digital signature hash, key derivation mechanism, stream cipher, or pseuo-random number generator. Skein supports internal state sizes of , and bits, and arbitrary output lengths.

  • SM3: SM3 is a bit hash function operating on bit input blocks. Part of a Chinese National Standard, SM3 is issued by the Chinese State Cryptographic Authority as GM/T SM3 cryptographic hash algorithm () and GB/T Information security techniques—SM3 cryptographic hash algorithm (). More information can also be found at the SM3 (hash function) page.

  • Tiger: Designed by Ross Anderson and Eli Biham, Tiger is designed to be secure, run efficiently on bit processors, and easily replace MD4, MD5, SHA and SHA-1 in other applications. Tiger/ produces a bit output and is compatible with bit architectures; Tiger/ and Tiger/ produce a hash of length and bits, respectively, to provide compatibility with the other hash functions mentioned above.

  • Whirlpool: Designed by V. Rijmen (co-inventor of Rijndael) and P.S.L.M. Barreto, Whirlpool is one of two hash functions endorsed by the NESSIE competition (the other being SHA). Whirlpool operates on messages less than 2 bits in length and produces a message digest of bits. The design of this hash function is very different than that of MD5 and SHA-1, making it immune to the types of attacks that succeeded on those hashes.

Readers might be interested in HashCalc, a Windows-based program that calculates hash values using a dozen algorithms, including MD5, SHA-1 and several variants, RIPEMD, and Tiger. Command line utilities that calculate hash values include sha_verify by Dan Mares (Windows; supports MD5, SHA-1, SHA-2) and md5deep (cross-platform; supports MD5, SHA-1, SHA, Tiger, and Whirlpool).


A digression on hash collisions. Hash functions are sometimes misunderstood and some sources claim that no two files can have the same hash value. This is in theory, if not in fact, incorrect. Consider a hash function that provides a bit hash value. There are, then, 2 possible hash values. But there are an infinite number of possible files and &#; >> 2. Therefore, there have to be multiple files &#; in fact, there have to be an infinite number of files! &#; that have the same bit hash value. (Now, while even this is theoretically correct, it is not true in practice because hash algorithms are designed to work with a limited message size, as mentioned above. For example, SHA-1, SHA, and SHA produce hash values that are , , and bits in length, respectively, and limit the message length to less than 264 bits; SHA and all SHA variants limit the message length to less than 2 bits. Nevertheless, hopefully you get my point &#; and, alas, even if you don't, do know that there are multiple files that have the same MD5 or SHA-1 hash values.)

The difficulty is not necessarily in finding two files with the same hash, but in finding a second file that has the same hash value as a given first file. Consider this example. A human head has, generally, no more than ~, hairs. Since there are more than 7 billion people on earth, we know that there are a lot of people with the same number of hairs on their head. Finding two people with the same number of hairs, then, would be relatively simple. The harder problem is choosing one person (say, you, the reader) and then finding another person who has the same number of hairs on their head as you have on yours.

This is somewhat similar to the Birthday Problem. We know from probability that if you choose a random group of ~23 people, the probability is about 50% that two will share a birthday (the probability goes up to % with a group of 70 people). However, if you randomly select one person in a group of 23 and try to find a match to that person, the probability is only about 6% of finding a match; you'd need a group of for a 50% probability of a shared birthday to one of the people chosen at random (and a group of more than 4, to obtain a % probability).

What is hard to do, then, is to try to create a file that matches a given hash value so as to force a hash value collision &#; which is the reason that hash functions are used extensively for information security and computer forensics applications. Alas, researchers as far back as found that practical collision attacks could be launched on MD5, SHA-1, and other hash algorithms and, today, it is generally recognized that MD5 and SHA-1 are pretty much broken. Readers interested in this problem should read the following:

  • AccessData. (, April). MD5 Collisions: The Effect on Computer Forensics. AccessData White Paper.
  • Burr, W. (, March/April). Cryptographic hash standards: Where do we go from here?IEEE Security & Privacy, 4(2),
  • Dwyer, D. (, June 3). SHA-1 Collision Attacks Now 252. SecureWorks Research blog.
  • Gutman, P., Naccache, D., & Palmer, C.C. (, May/June). When hashes collide. IEEE Security & Privacy, 3(3),
  • Kessler, G.C. (). The Impact of MD5 File Hash Collisions on Digital Forensic Imaging. Journal of Digital Forensics, Security & Law, 11(4),
  • Kessler, G.C. (). The Impact of SHA-1 File Hash Collisions on Digital Forensic Imaging: A Follow-Up Experiment. Journal of Digital Forensics, Security & Law, 11(4),
  • Klima, V. (, March). Finding MD5 Collisions - a Toy For a Notebook.
  • Lee, R. (, January 7). Law Is Not A Science: Admissibility of Computer Evidence and MD5 Hashes. SANS Computer Forensics blog.
  • Leurent, G. & Peyrin, T. (, January). SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust. Real World Crypto .
  • Leurent, G. & Peyrin, T. (, January). SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust.(paper)
  • Stevens, M., Bursztein, E., Karpman, P., Albertini, A., & Markov, Y. (). The first collision for full SHA
  • Stevens, M., Karpman, P., & Peyrin, T. (, October 8). Freestart collision on full SHA Cryptology ePrint Archive, Report /
  • Thompson, E. (, February). MD5 collisions and the impact on computer forensics. Digital Investigation, 2(1),
  • Wang, X., Feng, D., Lai, X., & Yu, H. (, August). Collisions for Hash Functions MD4, MD5, HAVAL and RIPEMD.
  • Wang, X., Yin, Y.L., & Yu, H. (, February 13). Collision Search Attacks on SHA1.

Readers are also referred to the Eindhoven University of Technology HashClash Project Web site. for For additional information on hash functions, see David Hopwood's MessageDigest Algorithms page and Peter Selinger's MD5 Collision Demo page. For historical purposes, take a look at the situation with hash collisions, circa , in RFC

In October , the SHA-1 Freestart Collision was announced; see a report by Bruce Schneier and the developers of the attack (as well as the paper above by Stevens et al. ()). In February , the first SHA-1 collision was announced on the Google Security Blog and Centrum Wiskunde & Informatica's Shattered page. See also the paper by Stevens et al. (), listed above. If ths isn't enough, see the SHA-1 is a Shambles Web page and the Leurent & Peyrin paper, listed above.

For an interesting twist on this discussion, read about the Nostradamus attack reported at Predicting the winner of the US Presidential Elections using a Sony PlayStation 3 (by M. Stevens, A.K. Lenstra, and B. de Weger, November ).


Finally, note that certain extensions of hash functions are used for a variety of information security and digital forensics applications, such as:

  • Hash libraries, aka hashsets, are sets of hash values corresponding to known files. A hashset containing the hash values of all files known to be a part of a given operating system, for example, could form a set of known good files, and could be ignored in an investigation for malware or other suspicious file, whereas as hash library of known child pornographic images could form a set of known bad files and be the target of such an investigation.
  • Rolling hashes refer to a set of hash values that are computed based upon a fixed-length "sliding window" through the input. As an example, a hash value might be computed on bytes of a file, then on bytes , , , etc.
  • Fuzzy hashes are an area of intense research and represent hash values that represent two inputs that are similar. Fuzzy hashes are used to detect documents, images, or other files that are close to each other with respect to content. See "Fuzzy Hashing" by Jesse Kornblum for a good treatment of this topic.

Why Three Encryption Techniques?

So, why are there so many different types of cryptographic schemes? Why can't we do everything we need with just one?

The answer is that each scheme is optimized for some specific cryptographic application(s). Hash functions, for example, are well-suited for ensuring data integrity because any change made to the contents of a message will result in the receiver calculating a different hash value than the one placed in the transmission by the sender. Since it is highly unlikely that two different messages will yield the same hash value, data integrity is ensured to a high degree of confidence.

Secret key cryptography, on the other hand, is ideally suited to encrypting messages, thus providing privacy and confidentiality. The sender can generate a session key on a per-message basis to encrypt the message; the receiver, of course, needs the same session key in order to decrypt the message.

Key exchange, of course, is a key application of public key cryptography (no pun intended). Asymmetric schemes can also be used for non-repudiation and user authentication; if the receiver can obtain the session key encrypted with the sender's private key, then only this sender could have sent the message. Public key cryptography could, theoretically, also be used to encrypt messages although this is rarely done because secret key cryptography values can generally be computed about times faster than public key cryptography values.

FIGURE 4: Use of the three cryptographic techniques for secure communication.


Figure 4 puts all of this together and shows how a hybrid cryptographic scheme combines all of these functions to form a secure transmission comprising a digital signature and digital envelope. In this example, the sender of the message is Alice and the receiver is Bob.

A digital envelope comprises an encrypted message and an encrypted session key. Alice uses secret key cryptography to encrypt her message using the session key, which she generates at random with each session. Alice then encrypts the session key using Bob's public key. The encrypted message and encrypted session key together form the digital envelope. Upon receipt, Bob recovers the session secret key using his private key and then decrypts the encrypted message.

The digital signature is formed in two steps. First, Alice computes the hash value of her message; next, she encrypts the hash value with her private key. Upon receipt of the digital signature, Bob recovers the hash value calculated by Alice by decrypting the digital signature with Alice's public key. Bob can then apply the hash function to Alice's original message, which he has already decrypted (see previous paragraph). If the resultant hash value is not the same as the value supplied by Alice, then Bob knows that the message has been altered; if the hash values are the same, Bob should believe that the message he received is identical to the one that Alice sent.

This scheme also provides nonrepudiation since it proves that Alice sent the message; if the hash value recovered by Bob using Alice's public key proves that the message has not been altered, then only Alice could have created the digital signature. Bob also has proof that he is the intended receiver; if he can correctly decrypt the message, then he must have correctly decrypted the session key meaning that his is the correct private key.

This diagram purposely suggests a cryptosystem where the session key is used for just a single session. Even if this session key is somehow broken, only this session will be compromised; the session key for the next session is not based upon the key for this session, just as this session's key was not dependent on the key from the previous session. This is known as Perfect Forward Secrecy; you might lose one session key due to a compromise but you won't lose all of them. (This was an issue in the OpenSSL vulnerability known as Heartbleed.)

The Significance of Key Length

In a article in the industry literature, a writer made the claim that bit keys did not provide as adequate protection for DES at that time as they did in because computers were times faster in than in Therefore, the writer went on, we needed 56,bit keys in instead of bit keys to provide adequate protection. The conclusion was then drawn that because 56,bit keys are infeasible (true), we should accept the fact that we have to live with weak cryptography (false!). The major error here is that the writer did not take into account that the number of possible key values double whenever a single bit is added to the key length; thus, a bit key has twice as many values as a bit key (because 257 is two times 256). In fact, a bit key would have times more values than a bit key.

But this does bring up the question &#; "What is the significance of key length as it affects the level of protection?"

In cryptography, size does matter. The larger the key, the harder it is to crack a block of encrypted data. The reason that large keys offer more protection is almost obvious; computers have made it easier to attack ciphertext by using brute force methods rather than by attacking the mathematics (which are generally well-known anyway). With a brute force attack, the attacker merely generates every possible key and applies it to the ciphertext. Any resulting plaintext that makes sense offers a candidate for a legitimate key. This was the basis, of course, of the EFF's attack on DES.

Until the mids or so, brute force attacks were beyond the capabilities of computers that were within the budget of the attacker community. By that time, however, significant compute power was typically available and accessible. General-purpose computers such as PCs were already being used for brute force attacks. For serious attackers with money to spend, such as some large companies or governments, Field Programmable Gate Array (FPGA) or Application-Specific Integrated Circuits (ASIC) technology offered the ability to build specialized chips that could provide even faster and cheaper solutions than a PC. As an example, the AT&T Optimized Reconfigurable Cell Array (ORCA) FPGA chip cost about $ and could test 30 million DES keys per second, while a $10 ASIC chip could test million DES keys per second; compare that to a PC which might be able to test 40, keys per second. Distributed attacks, harnessing the power of up to tens of thousands of powerful CPUs, are now commonly employed to try to brute-force crypto keys.

Type of AttackerBudgetToolTime and Cost
Per Key Recovered
Key Length Needed
For Protection
In Late
40 bits56 bits
Pedestrian HackerTinyScavenged
computer
time
1 weekInfeasible45
$FPGA5 hours
($)
38 years
($5,)
50
Small Business$10,FPGA12 minutes
($)
18 months
($5,)
55
Corporate Department$KFPGA24 seconds
($)
19 days
($5,)
60
ASIC seconds
($)
3 hours
($38)
Big Company$10MFPGA7 seconds
($)
13 hours
($5,)
70
ASIC seconds
($)
6 minutes
($38)
Intelligence Agency$MASIC seconds
($)
12 seconds
($38)
75

Table 2 &#; from a article discussing both why exporting bit keys was, in essence, no crypto at all and why DES' days were numbered &#; shows what DES key sizes were needed to protect data from attackers with different time and financial resources. This information was not merely academic; one of the basic tenets of any security system is to have an idea of what you are protecting and from whom are you protecting it! The table clearly shows that a bit key was essentially worthless against even the most unsophisticated attacker. On the other hand, bit keys were fairly strong unless you might be subject to some pretty serious corporate or government espionage. But note that even bit keys were clearly on the decline in their value and that the times in the table were worst cases.

So, how big is big enough? DES, invented in , was still in use at the turn of the century, nearly 25 years later. If we take that to be a design criteria (i.e., a plus year lifetime) and we believe Moore's Law ("computing power doubles every 18 months"), then a key size extension of 14 bits (i.e., a factor of more than 16,) should be adequate. The DES proposal suggested bit keys; by , a bit key would have been required to offer equal protection and an bit key necessary by

A or bit SKC key will probably suffice for some time because that length keeps us ahead of the brute force capabilities of the attackers. Note that while a large key is good, a huge key may not always be better; for example, expanding PKC keys beyond the current or bit lengths doesn't add any necessary protection at this time. Weaknesses in cryptosystems are largely based upon key management rather than weak keys.

Much of the discussion above, including the table, is based on the paper "Minimal Key Lengths for Symmetric Ciphers to Provide Adequate Commercial Security" by M. Blaze, W. Diffie, R.L. Rivest, B. Schneier, T. Shimomura, E. Thompson, and M. Wiener ().

The most effective large-number factoring methods today use a mathematical Number Field Sieve to find a certain number of relationships and then uses a matrix operation to solve a linear equation to produce the two prime factors. The sieve step actually involves a large number of operations that can be performed in parallel; solving the linear equation, however, requires a supercomputer. Indeed, finding the solution to the RSA challenge in February &#; factoring a digit (bit) prime number &#; required computers across the Internet about 4 weeks for the first step and a Cray computer hours and MB of memory to do the second step.

In early , Shamir (of RSA fame) described a new machine that could increase factorization speed by orders of magnitude. Although no detailed plans were provided nor is one known to have been built, the concepts of TWINKLE (The Weizmann Institute Key Locating Engine) could result in a specialized piece of hardware that would cost about $ and have the processing power of PCs. There still appear to be many engineering details that have to be worked out before such a machine could be built. Furthermore, the hardware improves the sieve step only; the matrix operation is not optimized at all by this design and the complexity of this step grows rapidly with key length, both in terms of processing time and memory requirements. Nevertheless, this plan conceptually puts bit keys within reach of being factored. Although most PKC schemes allow keys that are bits and longer, Shamir claims that bit RSA keys "protect 95% of today's E-commerce on the Internet." (See Bruce Schneier's Crypto-Gram (May 15, ) for more information.)

It is also interesting to note that while cryptography is good and strong cryptography is better, long keys may disrupt the nature of the randomness of data files. Shamir and van Someren ("Playing hide and seek with stored keys") have noted that a new generation of viruses can be written that will find files encrypted with long keys, making them easier to find by intruders and, therefore, more prone to attack.

Finally, U.S. government policy has tightly controlled the export of crypto products since World War II. Until the mids, export outside of North America of cryptographic products using keys greater than 40 bits in length was prohibited, which made those products essentially worthless in the marketplace, particularly for electronic commerce; today, crypto products are widely available on the Internet without restriction. The U.S. Department of Commerce Bureau of Industry and Security maintains an Encryption FAQ web page with more information about the current state of encryption registration.


Without meaning to editorialize too much in this tutorial, a bit of historical context might be helpful. In the mids, the U.S. Department of Commerce still classified cryptography as a munition and limited the export of any products that contained crypto. For that reason, browsers in the era, such as Internet Explorer and Netscape, had a domestic version with bit encryption (downloadable only in the U.S.) and an export version with bit encryption. Many cryptographers felt that the export limitations should be lifted because they only applied to U.S. products and seemed to have been put into place by policy makers who believed that only the U.S. knew how to build strong crypto algorithms, ignoring the work ongoing in Australia, Canada, Israel, South Africa, the U.K., and other locations in the s. Those restrictions were lifted by or , but there is still a prevailing attitude, apparently, that U.S. crypto algorithms are the only strong ones around; consider Bruce Schneier's blog in June titled "CIA Director John Brennan Pretends Foreign Cryptography Doesn't Exist." Cryptography is a decidedly international game today; note the many countries mentioned above as having developed various algorithms, not the least of which is the fact that NIST's Advanced Encryption Standard employs an algorithm submitted by cryptographers from Belgium. For more evidence, see Schneier's Worldwide Encryption Products Survey (February ).


On a related topic, public key crypto schemes can be used for several purposes, including key exchange, digital signatures, authentication, and more. In those PKC systems used for SKC key exchange, the PKC key lengths are chosen so as to be resistant to some selected level of attack. The length of the secret keys exchanged via that system have to have at least the same level of attack resistance. Thus, the three parameters of such a system &#; system strength, secret key strength, and public key strength &#; must be matched. This topic is explored in more detail in Determining Strengths For Public Keys Used For Exchanging Symmetric Keys (RFC ).

4. TRUST MODELS

Secure use of cryptography requires trust. While secret key cryptography can ensure message confidentiality and hash codes can ensure integrity, none of this works without trust. In SKC, Alice and Bob had to share a secret key. PKC solved the secret distribution problem, but how does Alice really know that Bob is who he says he is? Just because Bob has a public and private key, and purports to be "Bob," how does Alice know that a malicious person (Mallory) is not pretending to be Bob?

There are a number of trust models employed by various cryptographic schemes. This section will explore three of them:

  • The web of trust employed by Pretty Good Privacy (PGP) users, who hold their own set of trusted public keys.
  • Kerberos, a secret key distribution scheme using a trusted third party.
  • Certificates, which allow a set of trusted third parties to authenticate each other and, by implication, each other's users.

Each of these trust models differs in complexity, general applicability, scope, and scalability.

PGP Web of Trust

Pretty Good Privacy (described more below in Section ) is a widely used private e-mail scheme based on public key methods. A PGP user maintains a local keyring of all their known and trusted public keys. The user makes their own determination about the trustworthiness of a key using what is called a "web of trust."

FIGURE 5: GPG keychain.

Figure 5 shows a PGP-formatted keychain from the GNU Privacy Guard (GPG) software, an implementation of the OpenPGP standard. This is a section of my keychain, so only includes public keys from individuals whom I know and, presumably, trust. Note that keys are associated with e-mail addresses rather than individual names.

In general, the PGP Web of trust works as follows. Suppose that Alice needs Bob's public key. Alice could just ask Bob for it directly via e-mail or download the public key from a PGP key server; this server might a well-known PGP key repository or a site that Bob maintains himself. In fact, Bob's public key might be stored or listed in many places. (My public key, for example, can be found at storycall.us or at several public PGP key servers, including storycall.us.) Alice is prepared to believe that Bob's public key, as stored at these locations, is valid.

Suppose Carol claims to hold Bob's public key and offers to give the key to Alice. How does Alice know that Carol's version of Bob's key is valid or if Carol is actually giving Alice a key that will allow Mallory access to messages? The answer is, "It depends." If Alice trusts Carol and Carol says that she thinks that her version of Bob's key is valid, then Alice may &#; at her option &#; trust that key. And trust is not necessarily transitive; if Dave has a copy of Bob's key and Carol trusts Dave, it does not necessarily follow that Alice trusts Dave even if she does trust Carol.

The point here is that who Alice trusts and how she makes that determination is strictly up to Alice. PGP makes no statement and has no protocol about how one user determines whether they trust another user or not. In any case, encryption and signatures based on public keys can only be used when the appropriate public key is on the user's keyring.

Kerberos

Kerberos is a commonly used authentication scheme on the Internet. Developed by MIT's Project Athena, Kerberos is named for the three-headed dog who, according to Greek mythology, guards the entrance of Hades (rather than the exit, for some reason!).

Kerberos employs a client/server architecture and provides user-to-server authentication rather than host-to-host authentication. In this model, security and authentication will be based on secret key technology where every host on the network has its own secret key. It would clearly be unmanageable if every host had to know the keys of all other hosts so a secure, trusted host somewhere on the network, known as a Key Distribution Center (KDC), knows the keys for all of the hosts (or at least some of the hosts within a portion of the network, called a realm). In this way, when a new node is brought online, only the KDC and the new node need to be configured with the node's key; keys can be distributed physically or by some other secure means.

FIGURE 6: Kerberos architecture.


The Kerberos Server/KDC has two main functions (Figure 6), known as the Authentication Server (AS) and Ticket-Granting Server (TGS). The steps in establishing an authenticated session between an application client and the application server are:
  1. The Kerberos client software establishes a connection with the Kerberos server's AS function. The AS first authenticates that the client is who it purports to be. The AS then provides the client with a secret key for this login session (the TGS session key) and a ticket-granting ticket (TGT), which gives the client permission to talk to the TGS. The ticket has a finite lifetime so that the authentication process is repeated periodically.
  2. The client now communicates with the TGS to obtain the Application Server's key so that it (the client) can establish a connection to the service it wants. The client supplies the TGS with the TGS session key and TGT; the TGS responds with an application session key (ASK) and an encrypted form of the Application Server's secret key; this secret key is never sent on the network in any other form.
  3. The client has now authenticated itself and can prove its identity to the Application Server by supplying the Kerberos ticket, application session key, and encrypted Application Server secret key. The Application Server responds with similarly encrypted information to authenticate itself to the client. At this point, the client can initiate the intended service requests (e.g., Telnet, FTP, HTTP, or e-commerce transaction session establishment).

The current version of this protocol is Kerberos V5 (described in RFC ). While the details of their operation, functional capabilities, and message formats are different, the conceptual overview above pretty much holds for both. One primary difference is that Kerberos V4 uses only DES to generate keys and encrypt messages, while V5 allows other schemes to be employed (although DES is still the most widely algorithm used).

Public Key Certificates and Certificate Authorities

Certificates and Certificate Authorities (CA) are necessary for widespread use of cryptography for e-commerce applications. While a combination of secret and public key cryptography can solve the business issues discussed above, crypto cannot alone address the trust issues that must exist between a customer and vendor in the very fluid, very dynamic e-commerce relationship. How, for example, does one site obtain another party's public key? How does a recipient determine if a public key really belongs to the sender? How does the recipient know that the sender is using their public key for a legitimate purpose for which they are authorized? When does a public key expire? How can a key be revoked in case of compromise or loss?

The basic concept of a certificate is one that is familiar to all of us. A driver's license, credit card, or SCUBA certification, for example, identify us to others, indicate something that we are authorized to do, have an expiration date, and identify the authority that granted the certificate.

As complicated as this may sound, it really isn't. Consider driver's licenses. I have one issued by the State of Florida. The license establishes my identity, indicates the type of vehicles that I can operate and the fact that I must wear corrective lenses while doing so, identifies the issuing authority, and notes that I am an organ donor. When I drive in other states, the other jurisdictions throughout the U.S. recognize the authority of Florida to issue this "certificate" and they trust the information it contains. When I leave the U.S., everything changes. When I am in Aruba, Australia, Canada, Israel, and many other countries, they will accept not the Florida license, per se, but any license issued in the U.S. This analogy represents the certificate trust chain, where even certificates carry certificates.

For purposes of electronic transactions, certificates are digital documents. The specific functions of the certificate include:

  • Establish identity: Associate, or bind, a public key to an individual, organization, corporate position, or other entity.
  • Assign authority: Establish what actions the holder may or may not take based upon this certificate.
  • Secure confidential information (e.g., encrypting the session's symmetric key for data confidentiality).

Typically, a certificate contains a public key, a name, an expiration date, the name of the authority that issued the certificate (and, therefore, is vouching for the identity of the user), a serial number, any pertinent policies describing how the certificate was issued and/or how the certificate may be used, the digital signature of the certificate issuer, and perhaps other information.

FIGURE 7: VeriSign Class 3 certificate.

A sample abbreviated certificate is shown in Figure 7. This is a typical certificate found in a browser, in this case, Mozilla Firefox (MacOS). While this is a certificate issued by VeriSign, many root-level certificates can be found shipped with browsers. When the browser makes a connection to a secure Web site, the Web server sends its public key certificate to the browser. The browser then checks the certificate's signature against the public key that it has stored; if there is a match, the certificate is taken as valid and the Web site verified by this certificate is considered to be "trusted."

The most widely accepted certificate format is the one defined in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Recommendation X Rec. X is a specification used around the world and any applications complying with X can share certificates. Most certificates today comply with X Version 3 and contain the following information:

  • Version number
  • Certificate serial number
  • Signature algorithm identifier
  • Issuer's name and unique identifier
  • Validity (or operational) period
  • Subject's name and unique identifier
  • Subject public key information
  • Standard extensions
    • Certificate appropriate use definition
    • Key usage limitation definition
    • Certificate policy information
  • Other extensions
    • Application-specific
    • CA-specific

Certificate authorities are the repositories for public keys and can be any agency that issues certificates. A company, for example, may issue certificates to its employees, a college/university to its students, a store to its customers, an Internet service provider to its users, or a government to its constituents.

When a sender needs an intended receiver's public key, the sender must get that key from the receiver's CA. That scheme is straight-forward if the sender and receiver have certificates issued by the same CA. If not, how does the sender know to trust the foreign CA? One industry wag has noted, about trust: "You are either born with it or have it granted upon you." Thus, some CAs will be trusted because they are known to be reputable, such as the CAs operated by AT&T Services, Comodo, DigiCert (formerly GTE Cybertrust), EnTrust, Broadcom (formerly Symantec, formerly VeriSign), and Thawte. CAs, in turn, form trust relationships with other CAs. Thus, if a user queries a foreign CA for information, the user may ask to see a list of CAs that establish a "chain of trust" back to the user.

One major feature to look for in a CA is their identification policies and procedures. When a user generates a key pair and forwards the public key to a CA, the CA has to check the sender's identification and takes any steps necessary to assure itself that the request is really coming from the advertised sender. Different CAs have different identification policies and will, therefore, be trusted differently by other CAs. Verification of identity is just one of many issues that are part of a CA's Certification Practice Statement (CPS) and policies; other issues include how the CA protects the public keys in its care, how lost or compromised keys are revoked, and how the CA protects its own private keys.

As a final note, CAs are not immune to attack and certificates themselves are able to be counterfeited. One of the first such episodes occurred at the turn of the century; on January 29 and 30, , two VeriSign Class 3 code-signing digital certificates were issued to an individual who fraudulently claimed to be a Microsoft employee (CERT/CC CA and Microsoft Security Bulletin MS - Critical). Problems have continued over the years; good write-ups on this can be found at "Another Certification Authority Breached (the 12th!)" and "How Cybercrime Exploits Digital Certificates." Readers are also urged to read "Certification Authorities Under Attack: A Plea for Certificate Legitimation" (Oppliger, R., January/February , IEEE Internet Computing, 18(1), ).

As a partial way to address this issue, the Internet Security Research Group (ISRG) designed the Automated Certificate Management Environment (ACME) protocol. ACME is a communications protocol that streamlines the process of deploying a Public Key Infrastructure (PKI) by automating interactions between CAs and Web servers that wish to obtain a certificate. More information can be found at the Let's Encrypt Web site, an ACME-based CA service provided by the ISRG.

Summary

The paragraphs above describe three very different trust models. It is hard to say that any one is better than the others; it depends upon your application. One of the biggest and fastest growing applications of cryptography today, though, is electronic commerce (e-commerce), a term that itself begs for a formal definition.

PGP's web of trust is easy to maintain and very much based on the reality of users as people. The model, however, is limited; just how many public keys can a single user reliably store and maintain? And what if you are using the "wrong" computer when you want to send a message and can't access your keyring? How easy it is to revoke a key if it is compromised? PGP may also not scale well to an e-commerce scenario of secure communication between total strangers on short-notice.

Kerberos overcomes many of the problems of PGP's web of trust, in that it is scalable and its scope can be very large. However, it also requires that the Kerberos server have a priori knowledge of all client systems prior to any transactions, which makes it unfeasible for "hit-and-run" client/server relationships as seen in e-commerce.

Certificates and the collection of CAs will form a PKI. In the early days of the Internet, every host had to maintain a list of every other host; the Domain Name System (DNS) introduced the idea of a distributed database for this purpose and the DNS is one of the key reasons that the Internet has grown as it has. A PKI will fill a similar void in the e-commerce and PKC realm.

While certificates and the benefits of a PKI are most often associated with electronic commerce, the applications for PKI are much broader and include secure electronic mail, payments and electronic checks, Electronic Data Interchange (EDI), secure transfer of Domain Name System (DNS) and routing information, electronic forms, and digitally signed documents. A single "global PKI" is still many years away, that is the ultimate goal of today's work as international electronic commerce changes the way in which we do business in a similar way in which the Internet has changed the way in which we communicate.

5. CRYPTOGRAPHIC ALGORITHMS IN ACTION

The paragraphs above have provided an overview of the different types of cryptographic algorithms, as well as some examples of some available protocols and schemes. Table 3 provides a list of some other noteworthy schemes and cryptosystems employed &#; or proposed &#; for a variety of functions, most notably electronic commerce and secure communication. The paragraphs below will show several real cryptographic applications that many of us employ (knowingly or not) everyday for password protection and private communication. Some of the schemes described below never were widely deployed but are still historically interesting, thus remain included here. This list is, by no means, exhaustive but describes items that are of significant current and/or historic importance (a subjective judgement, to be sure).

BitmessageA decentralized, encrypted, peer-to-peer, trustless communications protocol for message exchange. The decentralized design, outlined in "Bitmessage: A Peer-to-Peer Message Authentication and Delivery System" (Warren, ), is conceptually based on the Bitcoin model.
CapstoneA now-defunct U.S. National Institute of Standards and Technology (NIST) and National Security Agency (NSA) project under the Bush Sr. and Clinton administrations for publicly available strong cryptography with keys escrowed by the government (NIST and the Treasury Dept.). Capstone included one or more tamper-proof computer chips for implementation (Clipper), a secret key encryption algorithm (Skipjack), digital signature algorithm (DSA), key exchange algorithm (KEA), and hash algorithm (SHA).
Challenge-Handshake Authentication Protocol (CHAP)An authentication scheme that allows one party to prove who they are to a second party by demonstrating knowledge of a shared secret without actually divulging that shared secret to a third party who might be listening. Described in RFC
Chips-Message Robust Authentication (CHIMERA)A scheme proposed for authenticating navigation data and the spreading code of civilian signals in the Global Positioning System (GPS). This is an anti-spoofing mechanism to protect the unencrypted civilian signals; GPS military signals are encrypted.
ClipperThe computer chip that would implement the Skipjack encryption scheme. The Clipper chip was to have had a deliberate backdoor so that material encrypted with this device would not be beyond the government's reach. Described in , Clipper was dead by See also EPIC's The Clipper Chip Web page.
Cryptography Research and Evaluation Committees (CRYPTEC)Similar in concept to the NIST AES process and NESSIE, CRYPTEC is the Japanese government's process to evaluate algorithms submitted for government and industry applications. CRYPTEX maintains a list of public key and secret key ciphers, hash functions, MACs, and other crypto algorithms approved for various applications in government environments.
Derived Unique Key Per Transaction (DUKPT)A key management scheme used for debit and credit card verification with point-of-sale (POS) transaction systems, automated teller machines (ATMs), and other financial applications. In DUKPT, a unique key is derived for each transaction based upon a fixed, shared key in such a way that knowledge of one derived key does not easily yield knowledge of other keys (including the fixed key). Therefore, if one of the derived keys is compromised, neither past nor subsequent transactions are endangered. DUKPT is specified in American National Standard (ANS) ANSI X (Retail Financial Services Symmetric Key Management Part 1: Using Symmetric Techniques) and can be purchased at the ANSI X Web page.
ECRYPT Stream Cipher Project (eSTREAM)The eSTREAM project came about as a result of the failure of the NESSIE project to produce a stream cipher that survived cryptanalysis. eSTREAM ran from to with the primary purpose of promoting the design of efficient and compact stream ciphers. As of September , the eSTREAM suite contains seven sciphers.
Escrowed Encryption Standard (EES)Largely unused, a controversial crypto scheme employing the SKIPJACK secret key crypto algorithm and a Law Enforcement Access Field (LEAF) creation method. LEAF was one part of the key escrow system and allowed for decryption of ciphertext messages that had been intercepted by law enforcement agencies. Described more in FIPS PUB (archived; no longer in force).
Federal Information Processing Standards (FIPS)These computer security- and crypto-related FIPS PUBs are produced by the U.S. National Institute of Standards and Technology (NIST) as standards for the U.S. Government. Current Federal Information Processing Standards (FIPS) related to crytography include:
FortezzaA PCMCIA card developed by NSA that implements the Capstone algorithms, intended for use with the Defense Messaging Service (DMS). Originally called Tessera.
GOSTGOST is a family of algorithms defined in the Russian cryptographic standards. Although most of the specifications are written in Russian, a series of RFCs describe some of the aspects so that the algorithms can be used effectively in Internet applications:
  • RFC Additional Cryptographic Algorithms for Use with GOST , GOST R , GOST R , and GOST R Algorithms
  • RFC Using the GOST , GOST R , GOST R , and GOST R Algorithms with Cryptographic Message Syntax (CMS)
  • RFC Using the GOST R , GOST R , and GOST R Algorithms with the Internet X Public Key Infrastructure Certificate and CRL Profile
  • RFC GOST Encryption, Decryption, and Message Authentication Code (MAC) Algorithms
  • RFC GOST R Hash Function Algorithm
  • RFC GOST R Digital Signature Algorithm (Updates RFC GOST R )
  • RFC GOST R Block Cipher "Kuznyechik"
  • RFC Guidelines on the Cryptographic Algorithms to Accompany the Usage of Standards GOST R and GOST R
  • RFC GOST R Block Cipher "Magma"
IP Security (IPsec)The IPsec protocol suite is used to provide privacy and authentication services at the IP layer. An overview of the protocol suite and of the documents comprising IPsec can be found in RFC Other documents include:
  • RFC IP security architecture.
  • RFC IP Authentication Header (AH), one of the two primary IPsec functions; AH provides connectionless integrity and data origin authentication for IP datagrams and protects against replay attacks.
  • RFC IP Encapsulating Security Payload (ESP), the other primary IPsec function; ESP provides a variety of security services within IPsec.
  • RFC Extended Sequence Number (ESN) Addendum, allows for negotiation of a or bit sequence number, used to detect replay attacks.
  • RFC Cryptographic algorithm implementation requirements for ESP and AH.
  • RFC The Internet Key Exchange (IKE) protocol, version 2, providing for mutual authentication and establishing and maintaining security associations.
    • IKE v1 was described in three separate documents, RFC (application of ISAKMP to IPsec), RFC (ISAKMP, a framework for key management and security associations), and RFC (IKE, using part of Oakley and part of SKEME in conjunction with ISAKMP to obtain authenticated keying material for use with ISAKMP, and for other security associations such as AH and ESP). IKE v1 is obsoleted with the introduction of IKEv2.
  • RFC Cryptographic algorithms used with IKEv2.
  • RFC Crypto suites for IPsec, IKE, and IKEv2.
  • RFC The use of AES in CBC-MAC mode with IPsec ESP.
  • RFC The use of the Camellia cipher algorithm in IPsec.
  • RFC The Use of RSA/SHA-1 Signatures within Encapsulating Security Payload (ESP) and Authentication Header (AH).
  • RFC Describes AES-XCBC-PRF, a pseudo-random function derived from the AES for use with IKE.
  • RFC Describes use of the HMAC with MD5 algorithm for data origin authentication and integrity protection in both AH and ESP.
  • RFC Describes use of DES-CBC (DES in Cipher Block Chaining Mode) for confidentiality in ESP.
  • RFC Defines use of the NULL encryption algorithm (i.e., provides authentication and integrity without confidentiality) in ESP.
  • RFC Describes OAKLEY, a key determination and distribution protocol.
  • RFC Describes use of Cipher Block Chaining (CBC) mode cipher algorithms with ESP.
  • RFCs and Description of Photuris, a session-key management protocol for IPsec.

In addition, RFC describes Suite B Cryptographic Suites for IPsec and RFC describes the Suite B profile for IPsec.

IPsec was first proposed for use with IP version 6 (IPv6), but can also be employed with the current IP version, IPv4.

(See more detail about IPsec below in Section )

Internet Security Association and Key Management Protocol (ISAKMP/OAKLEY)ISAKMP/OAKLEY provide an infrastructure for Internet secure communications. ISAKMP, designed by the National Security Agency (NSA) and described in RFC , is a framework for key management and security associations, independent of the key generation and cryptographic algorithms actually employed. The OAKLEY Key Determination Protocol, described in RFC , is a key determination and distribution protocol using a variation of Diffie-Hellman.
KerberosA secret key encryption and authentication system, designed to authenticate requests for network resources within a user domain rather than to authenticate messages. Kerberos also uses a trusted third-party approach; a client communications with the Kerberos server to obtain "credentials" so that it may access services at the application server. Kerberos V4 used DES to generate keys and encrypt messages; Kerberos V5 uses DES and other schemes for key generation.

Microsoft added support for Kerberos V5 &#; with some proprietary extensions &#; in Windows Active Directory. There are many Kerberos articles posted at Microsoft's Knowledge Base, notably "Kerberos Explained."
Keyed-Hash Message Authentication Code (HMAC)A message authentication scheme based upon secret key cryptography and the secret key shared between two parties rather than public key methods. Described in FIPS PUB and RFC (See Section below for details on HMAC operation.)
Message Digest Cipher (MDC)Invented by Peter Gutman, MDC turns a one-way hash function into a block cipher.
MIME Object Security Services (MOSS)Designed as a successor to PEM to provide PEM-based security services to MIME messages. Described in RFC Never widely implemented and now defunct.
Mujahedeen SecretsA Windows GUI, PGP-like cryptosystem. Developed by supporters of Al-Qaeda, the program employs the five finalist AES algorithms, namely, MARS, RC6, Rijndael, Serpent, and Twofish. Also described in Inspire Magazine, Issue 1, pp. and Inspire Magazine, Issue 2, pp. Additional related information can also be found in "How Al-Qaeda Uses Encryption Post-Snowden (Part 2)."
New European Schemes for Signatures, Integrity and Encryption (NESSIE)NESSIE was an independent project meant to augment the work of NIST during the AES adoption process by putting out an open call for new cryptographic primitives. The NESSIE project ran from about While several new block ciper, PKC, MAC, and digital signature algorithms were found during the NESSIE process, no new stream cipher survived cryptanalysis. As a result, the ECRYPT Stream Cipher Project (eSTREAM) was created.
NSA Suite B CryptographyAn NSA standard for securing information at the SECRET level. Defines use of:
  • Advanced Encryption Standard (AES) with key sizes of and bits, per FIPS PUB for encryption
  • The Ephemeral Unified Model and the One-Pass Diffie Hellman (referred to as ECDH) using the curves with and bit prime moduli, per NIST Special Publication A for key exchange
  • Elliptic Curve Digital Signature Algorithm (ECDSA) using the curves with and bit prime moduli, per FIPS PUB for digital signatures
  • Secure Hash Algorithm (SHA) using and bits, per FIPS PUB for hashing

RFC describes Suite B Cryptographic Suites for Secure Shell (SSH) and RFC describes Suite B Cryptographic Suites for Secure IP (IPsec).

RFC reclassifies the RFCs related to the Suite B cryptographic algorithms as Historic, and it discusses the reasons for doing so.

Pretty Good Privacy (PGP)A family of cryptographic routines for e-mail, file, and disk encryption developed by Philip Zimmermann. PGP x uses RSA for key management and digital signatures, IDEA for message encryption, and MD5 for computing the message's hash value; more information can also be found in RFC PGP 5.x (formerly known as "PGP 3") uses Diffie-Hellman/DSS for key management and digital signatures; IDEA, CAST, or 3DES for message encryption; and MD5 or SHA for computing the message's hash value. OpenPGP, described in RFC , is an open definition of security software based on PGP 5.x. The GNU Privacy Guard (GPG) is a free software version of OpenPGP.

(See more detail about PGP below in Section )

Privacy Enhanced Mail (PEM)An IETF standard for secure electronic mail over the Internet, including provisions for encryption (DES), authentication, and key management (DES, RSA). Developed by the IETF but never widely used. Described in the following RFCs:
  • RFC Part I, Message Encryption and Authentication Procedures
  • RFC Part II, Certificate-Based Key Management
  • RFC Part III, Algorithms, Modes, and Identifiers
  • RFC Part IV, Key Certification and Related Services
Private Communication Technology (PCT)Developed by Microsoft for secure communication on the Internet. PCT supported Diffie-Hellman, Fortezza, and RSA for key establishment; DES, RC2, RC4, and triple-DES for encryption; and DSA and RSA message signatures. Never widely used; superceded by SSL and TLS.
Secure Electronic Transaction (SET)A communications protocol for securing credit card transactions, developed by MasterCard and VISA, in cooperation with IBM, Microsoft, RSA, and other companies. Merged two other protocols: Secure Electronic Payment Protocol (SEPP), an open specification for secure bank card transactions over the Internet developed by CyberCash, GTE, IBM, MasterCard, and Netscape; and Secure Transaction Technology (STT), a secure payment protocol developed by Microsoft and Visa International. Supports DES and RC4 for encryption, and RSA for signatures, key exchange, and public key encryption of bank card numbers. SET V is described in Book 1, Book 2, and Book 3. SET has been superceded by SSL and TLS.
Secure Hypertext Transfer Protocol (S-HTTP)An extension to HTTP to provide secure exchange of documents over the World Wide Web. Supported algorithms include RSA and Kerberos for key exchange, DES, IDEA, RC2, and Triple-DES for encryption. Described in RFC S-HTTP was never as widely used as HTTP over SSL (https).
Secure Multipurpose Internet Mail Extensions (S/MIME)An IETF secure e-mail scheme superceding PEM, and adding digital signature and encryption capability to Internet MIME messages. S/MIME Version is described in RFCs and , and employs the Cryptographic Message Syntax described in RFCs and

(More detail about S/MIME can be found below in Section )
Secure Sockets Layer (SSL)Developed in by Netscape Communications to provide application-independent security and privacy over the Internet. SSL is designed so that protocols such as HTTP, FTP (File Transfer Protocol), and Telnet can operate over it transparently. SSL allows both server authentication (mandatory) and client authentication (optional). RSA is used during negotiation to exchange keys and identify the actual cryptographic algorithm (DES, IDEA, RC2, RC4, or 3DES) to use for the session. SSL also uses MD5 for message digests and X public key certificates. SSL was found to be breakable soon after the IETF announced formation of group to work on TLS and RFC specifically prohibits the use of SSL v by TLS clients. SSL version is described in RFC All versions of SSL are now deprecated in favor of TLS; TLS v is sometimes referred to as "SSL v"

(More detail about SSL can be found below in Section )
Server Gated Cryptography (SGC)Microsoft extension to SSL that provided strong encryption for online banking and other financial applications using RC2 (bit key), RC4 (bit key), DES (bit key), or 3DES (equivalent of bit key). Use of SGC required an Windows NT Server running Internet Information Server (IIS) with a valid SGC certificate. SGC was available in bit Windows versions of Internet Explorer (IE) ; support for Mac, Unix, and bit Windows versions of IE was planned, but never materialized, and SGC was made moot when browsers started to ship with bit encryption.
ShangMi (SM) Cipher SuitesA suite of authentication, encryption, and hash algorithms from the People's Republic of China.
  • SM2 Cryptography Algorithm: A public key crypto scheme based on elliptic curves. An overview of the specification, in Chinese, can be found in GM/T Additional specifications can be found in:
  • SM3 Cryptographic Hash Algorithm: A hash algorithm operating on bit blocks to produce a bit hash value. Described in GB/T
  • SM4 Block Cipher Algorithm: A Feistel block cipher algorithm with a block length and key length of bits, and 32 rounds. Described in GB/T
An application of the ShangMi Cipher Suites in TLS can be found in RFC
Signal ProtocolA protocol for providing end-to-end encryption for voice calls, video calls, and instant messaging (including group chats). Employing a combination of AES, ECC, and HMAC algorithms, it offers such features as confidentiality, integrity, authentication, forward/future secrecy, and message repudiation. Signal is particularly interesting because of its lineage and widespread use. The Signal Protocol's earliest versions were known as TextSecure, first developed by Open Whisper Systems in TextSecure itself was based on a protocol called Off-the-Record (OTR) Messaging, designed as an improvement over OpenPGP and S/MIME. TextSecure v2 () introduced a scheme called the Axolotl Ratchet for key exchange and added additional communication features. After subsequent iterations improving key management (and the renaming of the key exchange protocol to Double Ratchet), additional cryptographic primitives, and the addition of an encrypted voice calling application (RedPhone), TextSecure was renamed Signal Protocol in The Ratchet key exchange algorithm is at the heart of the power of this system. Most messaging apps employ the users' public and private keys; the weakness here is that if the phone falls into someone else's hands, all of the messages on the device &#; including deleted messages &#; can be decrypted. The Ratchet algorithm generates a set of so-called "temporary keys" for each user, based upon that user's public/private key pair. When two users exchange messages, the Signal protocol creates a secret key by combining the temporary and permanent pairs of public and private keys for both users. Each message is assigned its own secret key. Because the generation of the secret key requires access to both users' private keys, it exists only on their two devices. The Signal Protocol is/has been employed in:
  • WhatsApp (introduced )
  • G Data Software's Secure Chat (introduced ; service discontinued )
  • Google's Allo app (introduced ; discontinued in favor of Messages app, )
  • Facebook Messenger (introduced )
  • Skype's Private Conversations mode (introduced )
  • All of Google's Rich Communication Services (RCS) on Android systems (introduced )
A reasonably good writeup of the protocol can be found in "Demystifying the Signal Protocol for End-to-End Encryption (E2EE)" by Kozhukhovskaya, Mora, and Wong ().
Simple Authentication and Security Layer (SASL)A framework for providing authentication and data security services in connection-oriented protocols (a la TCP), described in RFC It provides a structured interface and allows new protocols to reuse existing authentication mechanisms and allows old protocols to make use of new mechanisms.

It has been common practice on the Internet to permit anonymous access to various services, employing a plain-text password using a user name of "anonymous" and a password of an email address or some other identifying information. New IETF protocols disallow plain-text logins. The Anonymous SASL Mechanism (RFC ) provides a method for anonymous logins within the SASL framework.
Simple Key-Management for Internet Protocol (SKIP)Key management scheme for secure IP communication, specifically for IPsec, and designed by Aziz and Diffie. SKIP essentially defines a public key infrastructure for the Internet and even uses X certificates. Most public key cryptosystems assign keys on a per-session basis, which is inconvenient for the Internet since IP is connectionless. Instead, SKIP provides a basis for secure communication between any pair of Internet hosts. SKIP can employ DES, 3DES, IDEA, RC2, RC5, MD5, and SHA As it happened, SKIP was not adopted for IPsec; IKE was selected instead.
SM9Chinese Standard GM/T SM9 () is the Chinese national standard for Identity Based Cryptography. SM9 comprises three cryptographic algorithms, namely the Identity Based Digital Signature Algorithm, Identity Based Key Agreement Algorithm, and Identity Based Key Encapsulation Algorithm (allowing one party to securely send a symmetric key to another party). The SM9 scheme is also described in The SM9 Cryptographic Schemes (Z. Cheng).
TelegramTelegram, launched in , is a cloud-based instant messaging and voice over IP (VoIP) service, with client app software available for all major computer and mobile device operating systems. Telegram allows users to exchange messages, photos, videos, etc., and supplies end-to-end encryption using a protocol called MTProto. stickers, audio and files of any type. MTProto employs bit AES, bit RSA, and Diffie-Hellman key exchange. There have been several contriversies with Telegram, not the least of which has to do with the nationality of the founders and the true location of the business, as well as some operation issues. From a cryptological viewpoint, however, one cautionary tale can be found in "On the CCA (in)security of MTProto" (Jakobsen & Orlandi, ), who describe some of the crypto weaknesses of the protocol; specifically, that "MTProto does not satisfy the definitions of authenticated encryption (AE) or indistinguishability under chosen-ciphertext attack (IND-CCA)" (p. 1).
Transmission Control Protocol (TCP) encryption (tcpcrypt)As of , the majority of Internet TCP traffic is not encrypted. The two primary reasons for this are (1) many legacy protocols have no mechanism with which to employ encryption (e.g., without a command such as STARTSSL, the protocol cannot invoke use of any encryption) and (2) many legacy applications cannot be upgraded, so no new encryption can be added. The response from the IETF's TCP Increased Security Working Group was to define a transparent way within the transport layer (i.e., TCP) with which to invoke encryption. The TCP Encryption Negotiation Option (TCP-ENO) addresses these two problems with an out-of-band, fully backward-compatible TCP option with which to negotiate use of encryption. TCP-ENO is described in RFC and tcpcrypt, an encryption protocol to protect TCP streams, is described in RFC
Transport Layer Security (TLS)TLS v is an IETF specification (RFC ) intended to replace SSL v TLS v employs Triple-DES (secret key cryptography), SHA (hash), Diffie-Hellman (key exchange), and DSS (digital signatures). TLS v was vulnerable to attack and updated by v (RFC ), which is now classified as an HISTORIC specification. TLS v was replaced by TLS v (RFC ) and, subsequently, by v (RFC ).

TLS is designed to operate over TCP. The IETF developed the Datagram Transport Layer Security (DTLS) protocol to operate over UDP. DTLS v is described in RFC

(See more detail about TLS below in Section )
TrueCryptOpen source, multi-platform cryptography software that can be used to encrypt a file, partition, or entire disk. One of TrueCrypt's more interesting features is that of plausible deniability with hidden volumes or hidden operating systems. The original Web site, storycall.us, suddenly went dark in May The current fork of TrueCrypt is VeraCrypt.

(See more detail about TrueCrypt below in Section )
XITU-T recommendation for the format of certificates for the public key infrastructure. Certificates map (bind) a user identity to a public key. The IETF application of X certificates is documented in RFC An Internet X Public Key Infrastructure is further defined in RFC (Certificate Management Protocols) and RFC (Certificate Policy and Certification Practices Framework).

Password Protection

Nearly all modern multiuser computer and network operating systems employ passwords at the very least to protect and authenticate users accessing computer and/or network resources. But passwords are not typically kept on a host or server in plaintext, but are generally encrypted using some sort of hash scheme.

A) /etc/passwd file root:Jbw6BwE4XoUHoroot:/root:/bin/bash carol:FM5ikbQt1KCarol Monaghan:/home/carol:/bin/bash alex:LqAi7Mdyg/HcQAlex Insley:/home/alex:/bin/bash gary:FkJXupRyFqY4sGary Kessler:/home/gary:/bin/bash todd:edGqQUAaGv7gTodd Pritsky:/home/todd:/bin/bash josh:FiH0ONcjPut1gJoshua Kessler:/home/webroot:/bin/bash B.1) /etc/passwd file (with shadow passwords) root:xroot:/root:/bin/bash carol:xCarol Monaghan:/home/carol:/bin/bash alex:xAlex Insley:/home/alex:/bin/bash gary:xGary Kessler:/home/gary:/bin/bash todd:xTodd Pritsky:/home/todd:/bin/bash josh:xJoshua Kessler:/home/webroot:/bin/bash B.2) /etc/shadow file root:AGFw$1$P4u/uhLK$storycall.us35rlu65WlfCzq carol:kjHaN%35a8xMM8a/0kMl1?fwtLAM.K&kw alex:1$1KKmfTy0a7#storycall.us9a8H71lkwn/.hH22a gary:9ajlknknKJHjhnuypnAIJKL$storycall.us toddPOJ90uab6.k$klPqMt%alMlprWqu6$ josh:Awmqpsui*pjnsnJJK%aappaMpQo

FIGURE 8: Sample entries in Unix/Linux password files.

Unix/Linux, for example, uses a well-known hash via its crypt() function. Passwords are stored in the /etc/passwd file (Figure 8A); each record in the file contains the username, hashed password, user's individual and group numbers, user's name, home directory, and shell program; these fields are separated by colons (:). Note that each password is stored as a byte string. The first two characters are actually a salt, randomness added to each password so that if two users have the same password, they will still be encrypted differently; the salt, in fact, provides a means so that a single password might have different encryptions. The remaining 11 bytes are the password hash, calculated using DES.

As it happens, the /etc/passwd file is world-readable on Unix systems. This fact, coupled with the weak encryption of the passwords, resulted in the development of the shadow password system where passwords are kept in a separate, non-world-readable file used in conjunction with the normal password file. When shadow passwords are used, the password entry in /etc/passwd is replaced with a "*" or "x" (Figure 8B.1) and the MD5 hash of the passwords are stored in /etc/shadow along with some other account information (Figure 8B.2).

Windows NT uses a similar scheme to store passwords in the Security Access Manager (SAM) file. In the NT case, all passwords are hashed using the MD4 algorithm, resulting in a bit (byte) hash value (they are then obscured using an undocumented mathematical transformation that was a secret until distributed on the Internet). The password password, for example, might be stored as the hash value (in hexadecimal) b22d73c34bd4aa79c8b09f

Passwords are not saved in plaintext on computer systems precisely so they cannot be easily compromised. For similar reasons, we don't want passwords sent in plaintext across a network. But for remote logon applications, how does a client system identify itself or a user to the server? One mechanism, of course, is to send the password as a hash value and that, indeed, may be done. A weakness of that approach, however, is that an intruder can grab the password off of the network and use an off-line attack (such as a dictionary attack where an attacker takes every known word and encrypts it with the network's encryption algorithm, hoping eventually to find a match with a purloined password hash). In some situations, an attacker only has to copy the hashed password value and use it later on to gain unauthorized entry without ever learning the actual password.

An even stronger authentication method uses the password to modify a shared secret between the client and server, but never allows the password in any form to go across the network. This is the basis for the Challenge Handshake Authentication Protocol (CHAP), the remote logon process used by Windows NT.

As suggested above, Windows NT passwords are stored in a security file on a server as a byte hash value. In truth, Windows NT stores two hashes; a weak hash based upon the old LAN Manager (LanMan) scheme and the newer NT hash. When a user logs on to a server from a remote workstation, the user is identified by the username, sent across the network in plaintext (no worries here; it's not a secret anyway!). The server then generates a bit random number and sends it to the client (also in plaintext). This number is the challenge.

Using the LanMan scheme, the client system then encrypts the challenge using DES. Recall that DES employs a bit key, acts on a bit block of data, and produces a bit output. In this case, the bit data block is the random number. The client actually uses three different DES keys to encrypt the random number, producing three different bit outputs. The first key is the first seven bytes (56 bits) of the password's hash value, the second key is the next seven bytes in the password's hash, and the third key is the remaining two bytes of the password's hash concatenated with five zero-filled bytes. (So, for the example above, the three DES keys would be b22d73c34, bd4aa79c8b0, and 9f) Each key is applied to the random number resulting in three bit outputs, which comprise the response. Thus, the server's 8-byte challenge yields a byte response from the client and this is all that would be seen on the network. The server, for its part, does the same calculation to ensure that the values match.

There is, however, a significant weakness to this system. Specifically, the response is generated in such a way as to effectively reduce byte hash to three smaller hashes, of length seven, seven, and two, respectively. Thus, a password cracker has to break at most a 7-byte hash. One Windows NT vulnerability test program that I used in the past reported passwords that were "too short," defined as "less than 8 characters." When I asked how the program knew that passwords were too short, the software's salespeople suggested to me that the program broke the passwords to determine their length. This was, in fact, not the case at all; all the software really had to do was to look at the last eight bytes of the Windows NT LanMan hash to see that the password was seven or fewer characters.

Consider the following example, showing the LanMan hash of two different short passwords (take a close look at the last 8 bytes):

AA: 89D42A44EAAAAD3BBEE
AAA: 1C3A2B6DAAAD3BBEE

Note that the NT hash provides no such clue:

AA: CFBE79C8FD99FE7AAD8
AAA: 6B6E0FB2EDBC73B5BFB77

It is worth noting that the discussion above describes the Microsoft version of CHAP, or MS-CHAP (MS-CHAPv2 is described in RFC ). MS-CHAP assumes that it is working with hashed values of the password as the key to encrypting the challenge. More traditional CHAP (RFC ) assumes that it is starting with passwords in plaintext. The relevance of this observation is that a CHAP client, for example, cannot be authenticated by an MS-CHAP server; both client and server must use the same CHAP version.

Diffie-Hellman Key Exchange

Diffie and Hellman introduced the concept of public key cryptography. The mathematical "trick" of Diffie-Hellman key exchange is that it is relatively easy to compute exponents compared to computing discrete logarithms. Diffie-Hellman allows two parties &#; the ubiquitous Alice and Bob &#; to generate a secret key; they need to exchange some information over an unsecure communications channel to perform the calculation but an eavesdropper cannot determine the shared secret key based upon this information.

Diffie-Hellman works like this. Alice and Bob start by agreeing on a large prime number, N. They also have to choose some number G so that G<N.

There is actually another constraint on G, namely that it must be primitive with respect to N. Primitive is a definition that is a little beyond the scope of our discussion but basically G is primitive to N if the set of N-1 values of Gi mod N for i = (1,N-1) are all different. As an example, 2 is not primitive to 7 because the set of powers of 2 from 1 to 6, mod 7 (i.e., 21 mod 7, 22 mod 7, , 26 mod 7) = {2,4,1,2,4,1}. On the other hand, 3 is primitive to 7 because the set of powers of 3 from 1 to 6, mod 7 = {3,2,6,4,5,1}.

(The definition of primitive introduced a new term to some readers, namely mod. The phrase x mod y (and read as written!) means "take the remainder after dividing x by y." Thus, 1 mod 7 = 1, 9 mod 6 = 3, and 8 mod 8 = 0. Read more about the modulo function in the appendix.)

Anyway, either Alice or Bob selects N and G; they then tell the other party what the values are. Alice and Bob then work independently (Figure 9):

Alice

  1. Choose a large random number, XA < N. This is Alice's private key.
  2. Compute YA = GXA mod N. This is Alice's public key.
  3. Exchange public key with Bob.
  4. Compute KA = YBXA mod N
Bob

  1. Choose a large random number, XB < N. This is Bob's private key.
  2. Compute YB = GXB mod N. This is Bob's public key.
  3. Exchange public key with Alice.
  4. Compute KB = YAXB mod N
FIGURE 9: Diffie-Hellman key exchange model.

Note that XA and XB are kept secret while YA and YB are openly shared; these are the private and public keys, respectively. Based on their own private key and the public key learned from the other party, Alice and Bob have computed their secret keys, KA and KB, respectively, which are equal to GXAXB mod N.

Perhaps a small example will help here. Although Alice and Bob will really choose large values for N and G, I will use small values for example only; let's use N=7 and G=3, as shown in Figure

Alice

  1. Choose private key; XA = 2
  2. Compute public key; YA = 32 mod 7 = 2
  3. Exchange public key with Bob
  4. KA = YBXA mod N = 62 mod 7 = 1
Bob

  1. Choose private key; XB = 3
  2. Compute public key; YB = 33 mod 7 = 6
  3. Exchange public key with Alice
  4. KB = YAXB mod N = 23 mod 7 = 1
FIGURE Diffie-Hellman key exchange example.

In this example, then, Alice and Bob will both find the secret key 1 which is, indeed, 36 mod 7 (i.e., GXAXB = 32x3). If an eavesdropper (Eve) was listening in on the information exchange between Alice and Bob, she would learn G, N, YA, and YB which is a lot of information but insufficient to compromise the key; as long as XA and XB remain unknown, K is safe. As stated above, calculating Y = GX is a lot easier than finding X = logG Y.


A short digression on modulo arithmetic. In the paragraph above, we noted that 36 mod 7 = 1. This can be confirmed, of course, by noting that:

36 = = *7 + 1

There is a nice property of modulo arithmetic, however, that makes this determination a little easier, namely: (a mod x)(b mod x) = (ab mod x). Therefore, one possible shortcut is to note that 36 = (33)(33). Therefore, 36 mod 7 = (33 mod 7)(33 mod 7) = (27 mod 7)(27 mod 7) = 6*6 mod 7 = 36 mod 7 = 1.


Diffie-Hellman can also be used to allow key sharing amongst multiple users. Note again that the Diffie-Hellman algorithm is used to generate secret keys, not to encrypt and decrypt messages.

RSA Public Key Cryptography

Unlike Diffie-Hellman, RSA can be used for key exchange as well as digital signatures and the encryption of small blocks of data. Today, RSA is primarily used to encrypt the session key used for secret key encryption (message integrity) or the message's hash value (digital signature). RSA's mathematical hardness comes from the ease in calculating large numbers and the difficulty in finding the prime factors of those large numbers. Although employed with numbers using hundreds of digits, the math behind RSA is relatively straight-forward.

To create an RSA public/private key pair, here are the basic steps:

  1. Choose two prime numbers, p and q. From these numbers you can calculate the modulus, n = pq.
  2. Select a third number, e, that is relatively prime to (i.e., it does not divide evenly into) the product (p-1)(q-1). The number e is the public exponent.
  3. Calculate an integer d from the quotient (ed-1)/[(p-1)(q-1)]. The number d is the private exponent.

The public key is the number pair (n,e). Although these values are publicly known, it is computationally infeasible to determine d from n and e if p and q are large enough.

To encrypt a message, M, with the public key, create the ciphertext, C, using the equation:

The receiver then decrypts the ciphertext with the private key using the equation:

Now, this might look a bit complex and, indeed, the mathematics does take a lot of computer power given the large size of the numbers; since p and q may be digits (decimal) or more, d and e will be about the same size and n may be over digits. Nevertheless, a simple example may help. In this example, the values for p, q, e, and d are purposely chosen to be very small and the reader will see exactly how badly these values perform, but hopefully the algorithm will be adequately demonstrated:

  1. Select p=3 and q=5.
  2. The modulus n = pq =
  3. The value e must be relatively prime to (p-1)(q-1) = (2)(4) = 8. Select e=
  4. The value d must be chosen so that (ed-1)/[(p-1)(q-1)] is an integer. Thus, the value (11d-1)/[(2)(4)] = (11d-1)/8 must be an integer. Calculate one possible value, d=3.
  5. Let's suppose that we want to send a message &#; maybe a secret key &#; that has the numeric value of 7 (i.e., M=7). [More on this choice below.]
  6. The sender encrypts the message (M) using the public key value (e,n)=(11,15) and computes the ciphertext (C) with the formula C = 711 mod 15 =  mod 15 =
  7. The receiver decrypts the ciphertext using the private key value (d,n)=(3,15) and computes the plaintext with the formula M = 133 mod 15 =  mod 15 = 7.

I choose this trivial example because the value of n is so small (in particular, the value M cannot exceed n). But here is a more realistic example using larger d, e, and n values, as well as a more meaningful message; thanks to Barry Steyn for permission to use values from his How RSA Works With Examples page.

Let's say that we have chosen p and q so that we have the following value for n:





Let's also suppose that we have selected the public key, e, and private key, d, as follows:





Now suppose that our message (M) is the character string "attack at dawn" which has the numeric value (after converting the ASCII characters to a bit string and interpreting that bit string as a decimal number) of

The encryption phase uses the formula C = Me mod n, so C has the value:





The decryption phase uses the formula M = Cd mod n, so M has the value that matches our original plaintext:

This more realistic example gives just a clue as to how large the numbers are that are used in the real world implementations. RSA keylengths of and bits are considered to be pretty weak. The minimum suggested RSA key is bits; and bits are even better.

As an aside, Adam Back (storycall.us~adam/) wrote a two-line Perl script to implement RSA. It employs dc, an arbitrary precision arithmetic package that ships with most UNIX systems:

Источник: [storycall.us]

Comodo Internet Security

Comodo Internet Security (CIS) is developed and distributed by Comodo Group, a freemium Internet security suite that includes an antivirus program, personal firewall, sandbox, host-based intrusion prevention system (HIPS) and website filtering.

Version history[edit]

Release 5[edit]

In CIS cloud antivirus protection and spyware scanning capabilities were added. As it could not clean all the malware it found effectively, Comodo Cleaning Essentials was developed to supplement CIS.[4]

Host-based intrusion prevention system: Comodo's host-based intrusion prevention system (HIPS), named Defense+, is designed to provide protection against unknown malware. It is designed to restrict the actions of unknown applications, and restrict access to important files, folders, settings and the Windows Registry. Defense+ by default refuses any unknown program to install or execute except when specifically allowed by the user or when the file appears on Comodo's whitelist. In CIS a sandbox was added to Defense+ to isolate and run unknown applications.[5]

Release 6[edit]

CIS v6, released February , provided a major revision of the user interface and significant new features such as a fully sandboxed desktop environment.[6]

Release 7[edit]

On 6 March , Comodo announced completion of beta testing for CIS v7. Release 7 became official in April This release includes a new virus monitoring tool called VirusScope and Web Filtering features that provide control over user access to web content.[citation needed]

Release 8[edit]

Became official on 3 November It includes enhanced auto-sandboxing features.[7]

Release 10[edit]

Became official on 22 December [8] It includes Secure Shopping, prevention on malware intercepting during online transactions.[9][10]

Release 11[edit]

Became official on 26 June It includes many stability and performance changes.

Release 12[edit]

Became official on 26 March It includes extra functionality in creating rules and full support for Windows 10 October update.[11]

Comodo Endpoint Security Manager (CESM)[edit]

Comodo Endpoint Security Manager (CESM) is a server product for centrally managing the security settings and security components of network endpoint computers.[12] CESM manages the distribution and updates of antivirus and firewall software.[13][14][15]

The antivirus and firewall software managed by CESM are versions of the same software used by the consumer versions of Comodo Internet Security[16][17][18]

Reception[edit]

Reviews[edit]

PC Magazine lead security analyst, Neil J. Rubenking, reviewed Comodo Firewall Pro and Comodo Internet Security on 3 November , giving out of 5 to the first and to the second. He praised the suite's firewall capabilities but criticized its antimalware capabilities.[19][20] On 28 May , Roboert Vamosi of PC World reviewed Comodo Internet Security and gave it a score of 1 out of 5, criticizing it for its "disappointing malware detection" based on AV-TEST result and "limited feature set".[21]

Three years and three version later, Comodo Antivirus results became significantly better. On 30 January , Rubenking reviewed Comodo Internet Security Pro (v), giving it 4 stars out of 5. He praised its support service and antimalware features but was panned for its "effectively off by default" firewall, Defense+ popups, lack of parental control, antispam, antiphishing, and privacy protection features, and finally, "Low ratings from independent labs".[22]

In a 9 January review, Techworld awarded Comodo Internet Security Pro 4 of 5 stars and concluded "Cloud-based scanning and behaviour analysis joins a suite of top-notch security tools, designed to keep your PC secure. Recommended."[23] Also on the same date, Mike Williams of storycall.us reviewed Comodo Internet Security Pro and concluded "The program remains too complex for total PC beginners, we suspect. The average user will appreciate its largely automatic operation, though, while experts enjoy the powerful tools and extreme configurability."[24]

On 7 February , Comodo Internet Security Complete v6 earned the PC Magazine Editor's Choice award. Reviewing the software again, Neil J. Reubenking gave it a score of 5 stars, commended its support service, VPN solution, Comodo Secure DNS service and value for price but criticized its behavior blocker and its poor anti-phishing capabilities. Reubenking concluded "The biggest win for Comodo Internet Security Complete isn't in features, but in support. The GeekBuddy service fixes any problem, security or otherwise, using remote assistance. A Virus-Free Guarantee reimburses you for damage if malware gets past Comodo; you can also get reimbursed for expenses related to identity theft. Add a GeekBuddy-powered tuneup tool and an unusually powerful backup utility and you've got a winner."[25]

Once again, PC Magazine lead security analyst, Neil J. Rubenking, reviewed Comodo Internet Security in with very poor performance.[26]

Independent test labs[edit]

AV-TEST, an anti-virus test lab based in Germany, tested Comodo. Products that surpass the industry standard (measured by the mean score of the participating products) are awarded a certificate. Comodo Internet Security participated in their tests since , and for the first time in February , Comodo Internet Security Premium version obtained the AV-TEST certificate in the field of home products.[27]

On 18 January , Matousec, an independent tester of security software, analyzed 38 security products for their proactive defense capabilities and ranked Comodo Internet Security Premium (v6) number one. Comodo Internet Security was tested on Windows 7 SP1 with Internet Explorer 9 and passed out of tests (92%).[28][29] It was also ranked number 1 in [30]

See also[edit]

References[edit]

External links[edit]

Источник: [storycall.us]

F-Secure VPN Plus Client v5.0 crack serial keygen - much

An Overview of Cryptography

1. INTRODUCTION

Does increased security provide comfort to paranoid people? Or does security provide some very basic protections that we are naive to believe that we don't need? During this time when the Internet provides essential communication between literally billions of people and is used as a tool for commerce, social interaction, and the exchange of an increasing amount of personal information, security has become a tremendously important issue for every user to deal with.

There are many aspects to security and many applications, ranging from secure commerce and payments to private communications and protecting health care information. One essential aspect for secure communications is that of cryptography. But it is important to note that while cryptography is necessary for secure communications, it is not by itself sufficient. The reader is advised, then, that the topics covered here only describe the first of many steps necessary for better security in any number of situations.

This paper has two major purposes. The first is to define some of the terms and concepts behind basic cryptographic methods, and to offer a way to compare the myriad cryptographic schemes in use today. The second is to provide some real examples of cryptography in use today. (See Section A.4 for some additional commentary on this)

DISCLAIMER: Several companies, products, and services are mentioned in this tutorial. Such mention is for example purposes only and, unless explicitly stated otherwise, should not be taken as a recommendation or endorsement by the author.

2. BASIC CONCEPTS OF CRYPTOGRAPHY

Cryptography &#; the science of secret writing &#; is an ancient art; the first documented use of cryptography in writing dates back to circa B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription. Some experts argue that cryptography appeared spontaneously sometime after writing was invented, with applications ranging from diplomatic missives to war-time battle plans. It is no surprise, then, that new forms of cryptography came soon after the widespread development of computer communications. In data and telecommunications, cryptography is necessary when communicating over any untrusted medium, which includes just about any network, particularly the Internet.

There are five primary functions of cryptography:

  1. Privacy/confidentiality: Ensuring that no one can read the message except the intended receiver.
  2. Authentication: The process of proving one's identity.
  3. Integrity: Assuring the receiver that the received message has not been altered in any way from the original.
  4. Non-repudiation: A mechanism to prove that the sender really sent this message.
  5. Key exchange: The method by which crypto keys are shared between sender and receiver.

In cryptography, we start with the unencrypted data, referred to as plaintext. Plaintext is encrypted into ciphertext, which will in turn (usually) be decrypted back into usable plaintext. The encryption and decryption is based upon the type of cryptography scheme being employed and some form of key. For those who like formulas, this process is sometimes written as:

C = Ek(P)
P = Dk(C)

      where P = plaintext, C = ciphertext, E = the encryption method, D = the decryption method, and k = the key.

Given this, there are other functions that might be supported by crypto and other terms that one might hear:

  • Forward Secrecy (aka Perfect Forward Secrecy): This feature protects past encrypted sessions from compromise even if the server holding the messages is compromised. This is accomplished by creating a different key for every session so that compromise of a single key does not threaten the entirely of the communications.
  • Perfect Security: A system that is unbreakable and where the ciphertext conveys no information about the plaintext or the key. To achieve perfect security, the key has to be at least as long as the plaintext, making analysis and even brute-force attacks impossible. One-time pads are an example of such a system.
  • Deniable Authentication (aka Message Repudiation): A method whereby participants in an exchange of messages can be assured in the authenticity of the messages but in such a way that senders can later plausibly deny their participation to a third-party.

In many of the descriptions below, two communicating parties will be referred to as Alice and Bob; this is the common nomenclature in the crypto field and literature to make it easier to identify the communicating parties. If there is a third and fourth party to the communication, they will be referred to as Carol and Dave, respectively. A malicious party is referred to as Mallory, an eavesdropper as Eve, and a trusted third party as Trent.

Finally, cryptography is most closely associated with the development and creation of the mathematical algorithms used to encrypt and decrypt messages, whereas cryptanalysis is the science of analyzing and breaking encryption schemes. Cryptology is the umbrella term referring to the broad study of secret writing, and encompasses both cryptography and cryptanalysis.

3. TYPES OF CRYPTOGRAPHIC ALGORITHMS

There are several ways of classifying cryptographic algorithms. For purposes of this paper, they will be categorized based on the number of keys that are employed for encryption and decryption, and further defined by their application and use. The three types of algorithms that will be discussed are (Figure 1):

  • Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption; also called symmetric encryption. Primarily used for privacy and confidentiality.
  • Public Key Cryptography (PKC): Uses one key for encryption and another for decryption; also called asymmetric encryption. Primarily used for authentication, non-repudiation, and key exchange.
  • Hash Functions: Uses a mathematical transformation to irreversibly "encrypt" information, providing a digital fingerprint. Primarily used for message integrity.
print pack"C*",split/\D+/,`echo "16iII*o\U@{$/=$z;[(pop,pop,unpack"H*",<> )]}\EsMsKsN0[lN*1lK[d2%Sa2/d0<X+d*lMLa^*lN%0]dsXx++lMlN/dsM0<J]dsJxp"

This is a listing of all casks available from the cask tap via the Homebrew package manager for macOS.

0-ad0 A.D.b-alpha
editor Editor
browserBrowser
1clipboard1Clipboard
1password1Password
1password-cli1Password CLI
safe Total Security
3dgenceslicer3DGence Slicer,
4k-slideshow-maker4K Slideshow Maker
4k-stogram4K Stogram
4k-video-downloader4K Video Downloader
4k-video-to-mp34K Video to MP3
4k-youtube-to-mp34K YouTube to MP3
4peaks4Peaks
5kplayer5KPlayer,
8bitdo-ultimate-software8BitDo Ultimate Software
8x8-meet8x8 Meet
8x8-work8x8_work
a-better-finder-attributesA Better Finder Attributes
a-better-finder-renameA Better Finder Rename
a-slower-speed-of-lightA Slower Speed of Light
ableton-live-introAbleton Live Intro
ableton-live-liteAbleton Live Lite
ableton-live-standardAbleton Live Standard
ableton-live-suiteAbleton Live Suite
abricotineabricotine
abscissaAbscissa
abstractAbstract
abyssoft-teleportteleport
accessmenubarappsAccessMenuBarApps,15
accordanceAccordance Bible Software
accuricsAccurics CLI
ace-linkAce Link
acornAcorn,
acousticbrainz-guiAcousticBrainz
acquia-devAcquia Dev Desktop
acronis-true-imageAcronis True Image
acslogoACSLogo
activedockActiveDock,
activitywatchActivityWatch
actualActual
actual-odbc-packActual ODBC Driver Packlatest
adapterAdapter
adguardAdguard
adguard-vpnAdguard VPN
adiumAdium
adobe-acrobat-proAdobe Acrobat Pro DC
adobe-acrobat-readerAdobe Acrobat Reader DC
adobe-airAdobe AIR
adobe-connectAdobe Connect11,
adobe-creative-cloudAdobe Creative Cloud
adobe-creative-cloud-cleaner-toolAdobe Creative Cloud Cleaner Tool
adobe-digital-editionsAdobe Digital Editions
adobe-dng-converterAdobe DNG Converter
adoptopenjdkAdoptOpenJDK Java Development Kit,9
adriveAliyundrivelatest
advancedrestclientAdvanced REST Client
aegisubAegisub
aerialAerial Screensaver
aetherAetherdev,
aexol-remote-mouseAexol Remote Mouse,5
affinity-designerAffinity Designer
affinity-photoAffinity Photo
affinity-publisherAffinity Publisher
after-dark-classicAfter Dark Classic Set
agendaAgenda,
aimersoft-video-converter-ultimateAimersoft Video Converter Ultimate
aio-creator-neoAIO CREATOR NEO
air-connectAir Connect,
air-video-server-hdAir Video Server HDbeta1u1,
airbuddyAirBuddy,
aircallAircall
airdisplayAir Display,
airdroidAirDroid
airflowAirflow
airfoilAirfoil
airmediaCrestron AirMedia
airparrotAirParrot
airpassAirpass
airqmonAirqmon
airserverAirServer
airtableAirtable
airtameAirtame
airtoolAirtool,10
airtrashairtrash
airunlockAirUnlock
airyAiry,
aja-system-testAJA System Test
ajourAjour
alacrittyAlacritty
aladinAladin Desktop
alchemyAlchemy
aldenteAlDente
aleo-studioAleo Studio
aleph-oneAleph One
alfaviewAlfaview
alfredAlfred,
algodooAlgodoo
alinof-timerAlinof Timer
alipay-development-assistantAlipay Development Assistant
aliworkbenchAliWorkBench,LqEYADnbwALXMQ
all-in-one-messengerAll-in-One Messenger
alloyAlloy
almightyalmighty,32
alt-cAlt-C
altair-graphql-clientAltair GraphQL Client
altdeployAltDeploy
alternoteAlternote,
altserverAltServer,59
alttabAltTab
alvaAlva
amadeus-proAmadeus Pro
amadineAmadine,
amazon-chimeAmazon Chime
amazon-musicAmazon Music,_a
amazon-photosAmazon Drivelatest
amazon-workdocsAmazon WorkDocs,99
amazon-workdocs-driveAmazon WorkDocs Drivelatest
amazon-workspacesAmazon Workspaces
amd-power-gadgetAMD Power Gadget
amethystAmethyst
amitvpipPiP
ammAMM
ammoniteAmmonite,
amorphousdiskmarkAmorphousDiskMark,9
amppsAMPPS
anacondaContinuum Analytics Anaconda
ananas-analytics-desktop-editionAnanas Analytics Desktop Edition
android-commandlinetoolsAndroid SDK Command-line Tools
android-file-transferAndroid File Transfer
android-messagesAndroid Messages Desktop
android-ndkAndroid NDK22b
android-platform-toolsAndroid SDK Platform-Tools,e8b2b4cbe47c
android-sdkandroid-sdk
android-studioAndroid Studio
androidtoolAndroidTool
angbandAngband
angry-ip-scannerAngry IP Scanner
anka-build-cloud-controller-and-registryAnka Build Cloud Controller & Registry,f5
anka-build-cloud-registryAnka Build Cloud Registry,c83fd
anka-virtualizationAnka Virtualization
ankamaAnkama Launcher
ankiAnki
ankiapp-ankiAnkiApp
anonymAnonym
anonymousvpnAnonymous VPN
another-redis-desktop-managerAnother Redis Desktop Manager
ansible-dkAnsible DK,3
antconcAntConc
anybarAnyBar
anydeskAnyDesk
anydostorycall.us
anylistAnyList,2
aoAo
apache-couchdbApache CouchDB
apache-directory-studioApache Directory StudiovM17
apk-icon-editorAPK Icon Editor
app-cleanerNektony App Cleaner & Uninstaller,
app-tamerAppTamer,
apparencyApparency,
appcleanerFreeMacSoft AppCleaner,
appcodeAppCode,
appdeleteAppDelete
appgate-sdp-clientAppGate SDP Client for macOS
appgridAppGrid
appiumAppium Server Desktop GUI
apple-eventsApple Events
apple-juiceApple Juice
applepi-bakerApplePi-Baker
apppoliceAppPolice
appstore-quickviewAppStore Quickview
apptivateApptivate,15
apptrapAppTrap
appzapperAppZapper
aptanastudioAptana Studio
aptibleAptible Toolbelt,,
aqua-data-studioAquafold Aqua Data Studio
aquamacsAquamacs
aquaskkAquaSKK
aquatermAquaTerm
araxis-mergeAraxis Merge
archipelagoArchipelago
archiverArchiver
arduinoArduino
aria-maestosaAria Maestosa
aria2dAria2D,
aria2guiAria2GUI
ariangAriaNg Native
ark-desktop-walletArk Desktop Wallet
arkiwiArKiwi,
armoryArmory
aroundAround
arqArq
arq-cloud-backupArq Cloud Backup
arrsyncarRsync
art-directors-toolkitArt Directors Toolkit
artisanArtisan
artpipArtpip
asanaAsana
asc-timetablesaSc TimeTables
ascensionAscension
asciidocfxAsciidocFX
asset-catalog-tinkererAsset Catalog Tinkerer
assinador-serproassinador-serpro
astah-professionalChange Vision Astah Professional,bdf
astah-umlChange Vision Astah UML,bdf
astro-command-centerASTRO Command Centerlatest
astropadAstropad,
astropad-studioAstropad Studio,
atemoscatemOSC
atextaText,
atlantisAtlantis
atlauncherATLauncher
atokATOK,try3
atomGithub Atom
atomic-walletAtomic Wallet
au-labAU Lab
audacityAudacity
audio-hijackAudio Hijack
audiobook-builderAudiobook Builder
audiogridder-pluginAudioGridder Plugin
audiogridder-serverAudioGridder Server
audioscrobblerAudioscrobbler
audioslicerAudioSlicer
audirvanaAudirvana,
audiusAudius
augurAugur
auralAural Player
aurora-hdrAurora HDR,
auryoAuryo
authyAuthy Desktop
autodesk-fusionAutodesk Fusion latest
autodmgAutoDMG
autofirmaAutoFirma
automuteAutoMute
autopkgrAutoPkgr
autovolumeAutoVolume
autumnAutumn
avast-secure-browserAvast Secure Browser
avast-secureline-vpnAvast SecureLine VPN
avast-securityAvast Security,
avg-antivirusAVG Antivirus for Mac,
aviatrix-vpn-clientAviatrix VPN Client
avibrazil-rdmRDM
avidcodecsleAvid Codecs LE,3B39AE16
avidemuxAvidemux
avira-antivirusAvira Antiviruslatest
avitoolsAVItools
avocodeAvocode
avogadroAvogadro
avtouchbarAVTouchBar,
awaAWA
awareAware
awarenessAwareness
awips-pythonAWIPS Pythonlatest
aws-vaultaws-vault
aws-vpn-clientAWS Client VPN
axure-rpAxure RP
azirevpnAzireVPN
azure-data-studioAzure Data Studio
babeleditBabelEdit
back-in-timeBack-In-Time
backblazeBackblaze
backblaze-downloaderBackblaze Downloader
background-musicBackground Music
backlogBacklog
backuploupeBackupLoupe,
badlion-clientBadlion Client
baiduinputBaidu Inputlatest
baidunetdiskBaidu NetDisk
balance-lockBalance Lock,
balenaetcherEtcher
ballastballast
balsamiq-wireframesBalsamiq Wireframes
bandageBandage
bankidBankID
banking-4Banking 4,
banksiaguiBanksiaGui
banktivityBanktivity
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baretorrentbaretorrent
baritoneBaritone
barrierBarrier
bartenderBartender,
baseMenial Base,
basecampBasecamp3
basictexBasicTeX
batchmodBatChmodb5,
bathyscapheBathyScaphe,
batteriesBatteries
battery-buddyBattery Buddy,11
battery-reportBattery Report
battle-netBlizzard storycall.uslatest
battlescribeBattleScribe
baudlinebaudline
bbc-iplayer-downloadsBBC iPlayer Downloads
bbeditBBEdit
bdashBdash
bdinfoBDInfo
beacon-scannerBeaconScanner
beaker-browserBeaker Browser
beamerBeamer,
beanBean
beardedspiceBeardedSpice
beatunesbeaTunes
beeBee,
beekeeper-studioBeekeeper Studio
beeperBeeper
beersmithBeerSmith
berrycastBerrycast
bespokeBespoke Synth
bestresBestRes,
betaflight-configuratorBetaflight-Configurator
betelgueseBetelguese
better-window-managerBetter Window Manager,15
betterdiscord-installerbetterdiscord
betterdummybetterdummy
bettertouchtoolBetterTouchTool,
betterzipBetterZip
betweenBetween
betwixtBetwixt
beyond-compareBeyond Compare
bfxrBfxr
bibdeskBibDesk,
big-mean-folder-machineBig Mean Folder Machine
biglybtbiglybt
bilibiliBilibili
biliminibilimini
billings-proBillings Pro,
binanceBinance
binary-ninjaBinary Ninja
bingpaperBingPaper,46
binoBino
biopassfidoBioPass FIDO2 Manager
birdfontBirdFont
biscuitBiscuit
bisqBisq
bit-fiddleBit Fiddle
bit-slicerBit Slicer
bitbarBitBar
bitcoin-coreBitcoin Core
bitmessageBitmessage
bitrix24Bitrix24
bitsharesBitShares
bitwardenBitwarden
bitwig-studioBitwig Studio
black-inkBlack Ink,
blackholechBlackHole 16ch
blackhole-2chBlackHole 2ch
blackholechBlackHole 64ch
blenderBlender
blender-benchmarkBlender Open Data Benchmark
bleunlockBLEUnlock
blheli-configuratorBLHeli Configurator
blink1controlBlink1Control
bliskBlisk Browser
blitzBlitz
blobby-volley2Blobby Volley 2
blobsaverblobsaver
blockbenchBlockbench
blockblockBlockBlock
blockstackBlockstack
blocsBlocs,
bloodhoundbloodhound
bloomrpcBloomRPC
blu-ray-playerMacgo Mac Blu-ray Player,_
blu-ray-player-proMacgo Mac Blu-ray Player Pro,_
bluefishBluefish
bluegriffonBlueGriffon
blueharvestBlueHarvest
bluejBlueJ
bluejeansBlueJeans
bluesenseBlueSense,
bluesnoozeBluesnooze
bluestacksBlueStacks,cc2d
bluetilityBluetility
bluewalletBlueWallet
blurredBlurred
bobBob
boincBerkeley Open Infrastructure for Network Computing
bome-networkBome Network
bonitastudiocommunityBonita Studio Community Editionu0
bonjeffBonjeff
bonjour-browserBonjour Browser
bookendsBookends
bookmacsterBookMacster
boomBoom,
boom-3dBoom 3D,
boopBoop
boost-notestorycall.us
boostnoteBoostnote
bootchampBootChamp
bootstrap-studioBootstrap Studio
bootxchangerBootXChanger
bossabossa
bot-framework-emulatorMicrosoft Bot Framework Emulator
bowtieBowtie,
box-driveBox Drive
box-notesBox Notes
box-syncBox Sync
box-toolsBox Toolslatest
boxcryptorBoxcryptor
boxerBoxer
boxofsnoo-fairmountFairmount
boxy-suiteBoxy Suitelatest
bracketsBrackets
brain-workshopBrain Workshop
brainfmstorycall.us
brave-browserBrave,
breaktimerBreakTimer
breitbandmessungBreitbandmessung
brewletBrewletuniversal
brewservicesmenubarBrew Services Menubar
brewtargetbrewtarget
briaBria,
bricklink-partdesignerPartDesigner_5
bricklink-studioStudio_1
bricksmithBricksmith
brightnessBrightness
brightness-syncBrightness Sync
briskBrisk
brisyncBrisync
brl-cad-mgedBRL-CAD
brookBrook
brooklynBrooklyn
browserosaurusBrowserosaurus
browserstacklocalBrowserStack Local Testing
btcpayserver-vaultBTCPayServer Vault
buboBubo
bucketsBuckets
bugdomBugdom
buildsettingextractorBuildSettingExtractor
bunchBunch,
bunqcommunity-bunqbunqDesktop
burnBurn
burp-suiteBurp Suite Community Edition
burp-suite-professionalBurp Suite Professional
busycalBusyCal,
busycontactsBusyContacts,
butlerButler,
buttBroadcast Using This Tool
butterButter
buttercupButtercup
bwanaBwana
bzflagBZFlag
c0reqbittorrentqBittorrent Enhanced Edition
cabalCabal
cacherCacher
caffeineCaffeine
cajviewerCAJViewer,10
cakebrewCakebrew
cakebrewjscakebrewjs
calcserviceCalcService
calendarCalendar II,
calibrecalibre
calmly-writerCalmly Writer
camedCAM Editor
camera-liveCamera Live11
camerabag-photoCameraBag
camo-studioCamo Studio,
camtasiaCamtasia
camunda-modelerCamunda Modeler
candybarCandyBar
cantataCantata
canvaCanva
caprineCaprine
captainCaptain
captinCaptin,
captionCaption
captoCapto,
carbon-copy-clonerCarbon Copy Cloner
cardhopCardhop,
caretCaret
cashnotifyCashNotify
castrcastr
catchCatch
catlightcatlight
cave-storyPixel Cave Story,2
ccleanerPiriform CCleaner
ccmenuCCMenu
cctalkCCtalk
cd-tocd to
celestiaCelestia
celestialteapot-runwayRunway,
celldesignerCellDesigner
cellprofilerCellProfiler
cemuCEmu
cerebroCerebro
cernboxCERNBox Client
cevelopCevelop
chaiChai
chalkChalk
chameleon-ssd-optimizerChameleon SSD optimizerg
charlesCharles
charlessoft-timetrackerTimeTracker
chatmate-for-facebookChatMate for Facebook,
chatmate-for-whatsappChatMate for WhatsApp,
chatologyChatology
chatterinoChatterino
chattyChatty
chatworkChatWork
cheatsheetCheatSheet
checkra1ncheckra1n
cheetah3dCheetah3D
chef-workstationChef Workstation
chemdoodleChemDoodle
chessxChessX
chiaChia Blockchain
chiakiChiaki
chirpCHIRP
chocolatChocolat
choosyChoosy
chrome-devtoolsChrome DevTools
chrome-remote-desktop-hostChrome Remote Desktop
chromedriverChromeDriver
chromiumChromium
chronicleChronicle,
chronoagentChronoAgent
chronosChronos Timetracker
chronosyncChronoSync
chronycontrolChronyControl,
chrysalisChrysalis
cinc-workstationCinc Workstation
cinchCinch,
cincoCinco
cinderCinder
cinderellaCinderellab
cinebenchCinebenchR23,
circuitjs1Falstad CircuitJS
cirrusCirrus,
cisco-jabberCisco Jabber
cisco-proximityCisco Proximitydesktop
cisdem-data-recoveryCisdem Data Recovery
cisdem-document-readerCisdem Document Reader
cisdem-pdf-converter-ocrCisdem PDF Converter OCR
cisdem-pdfmanagerultimateCisdem PDFManagerUltimate
citraCitralatest
cityofzion-neonNeon Wallet
ckanComprehensive Kerbal Archive Network
ckb-nextckb-next
clamxavClamXAV,
clash-for-windowsClash for Windows
clashxClashX
classicftpClassicFTP
classroom-assistantGitHub Classroom Assistant
classroom-mode-for-minecraftClassroom Mode for Minecraft
clayclay
clean-meClean-me
cleanappSynium Software CleanApp
cleanmymacCleanMyMac X,
cleanshotCleanShot
cleartextCleartext
clementineClementine
clickchartsClickCharts
clicker-for-netflixClicker for Netflix
clicker-for-youtubeClicker for YouTube,52
clickupClickUp
clionCLion,
clip-studio-paintClip Studio Paint
clipgrabClipGrab
clipyClipy
clixCLIX
cljstylecljstyle
clockClock
clock-barClock Bar,
clock-signalClock Signal
clockerClocker
clockifyClockify,
clocksaverstorycall.us screensaver
clone-heroClone Hero
clonkClonk Rage
cloud-pbxCloud PBX
cloudappCloudApp,
cloudashcloudash
cloudcompareCloudComparelatest
cloudflare-warpCloudflare WARP,
cloudmounterEltima CloudMounter,
cloudupCloudup
cloudytabsCloudyTabs
clover-configuratorClover Configurator
cmakeCMake
cmd-eikanacmd-eikana
cmdtapCmdTap
cncjsCNSjs
cncnetCnCNet: Classic Command & Conquer
coarchicoArchi plugin for Archi
coccinellidaCoccinellida
coccocCốc Cốc,
cockatriceCockatrice,Prism
cocktailCocktail
cocoapodsstorycall.us
cocoarestclientCocoaRestClient
cocoaspellcocoAspell
coconutbatterycoconutBattery,cb
coconutidcoconutID
codaPanic Coda,
code-composer-studioCode Composer Studio (CCS)
code-notesCode Notes
codecrashplanCode42 CrashPlan,
codeexpanderCodeExpander
codekitCodeKit,
codeliteCodeLite
codeqlCodeQL
coderunnerCodeRunner,
codespaceCodespace
coffitivity-offlineCoffitivity Offline
cogCog,cb8
coin-walletCoin Wallet
coinomi-walletCoinomi Wallet
cold-turkey-blockerCold Turkey
color-oracleColor Oracle
colorchecker-camera-calibrationColorChecker Camera Calibration
colorpicker-developerDeveloper Color Picker
colorpicker-materialdesignMaterial Design
colorpicker-propickerPro Picker
colorpicker-skalacolorSkala Color
colorsnapperColorSnapper 2
colortesterColorTester
colorwellColorWell
colour-contrast-analyserColour Contrast Analyser (CCA)
combine-pdfsCombine PDFs
comictaggerComicTagger
comma-chameleonComma Chameleon
command-padCommand Pad
command-tab-plusCommand-Tab Plus,
commander-oneCommander One,
commandqCommandQ
composercatComposercat
compositorCompositor
conferencesstorycall.uslalpha22
connectiqGarmin Connect IQ SDK,,af9b
connectmenowConnectMeNow
consoleConsole
container-psContainer PS
contextsContexts,
continuity-activation-toolContinuity Activation Tool
contrasteContraste,
controllermateControllerMate
controlplaneControlPlane
convert3dguiConvert3DGUI
cookieCookie
cool-retro-termcool-retro-term
cooltermCoolTerm
copyclipCopyClip
copyqCopyQ
copytranslatorCopyTranslator
coqideCoq
cordCoRD,
core-data-editorCore Data Editor
corelocationcliCore Location CLI
cornercalCornerCal
cornerstoneCornerstone
corona-trackerCorona Tracker
correttoAWS Corretto JDK
coscreenCoScreen
coteditorCotEditor
couchbase-server-communityCouchbase Server
couchbase-server-enterpriseCouchbase Server
couchpotatoCouchPotato
couleursCouleurs,
countdownCountdown Screensaver
coverloadCoverLoad
cozy-driveCozy Drive
cpuinfocpuinfo
crCool Reader,10
craftmanagerCraftManager,
create-recovery-partition-installerCreate Recovery Partition Installer
createuserpkgCreateUserPkg
creepyCreepy
crescendoCrescendo
criptextCriptext,
cronnixCronniX
crossoverCrossOver
crosspack-avrCrossPack
crunchCrunch
crushftpCrushFTP10
cryocryo
crypterCrypter
cryptomatorCryptomator
cryptonomic-galleonGalleonb
cryptrCryptr
crystalmakerCrystalMaker
crystax-ndkCrystax NDK
cscreencscreen
cubicsdrCubicSDR
cuda-zCUDA-Z
cumulusCumulus
cura-lulzbotCura LulzBot Edition,ce3e47ac
curioCurio15,
curiosityCuriosity
curseforgeCurseForge
cursorcererCursorcererlatest
cursorsenseCursorSense
customshortcutsCustomShortcuts,
cutesdrCuteSDR
cutterCutter
cyberduckCyberduck,
cyberghost-vpnCyberGhost,
cyclingmaxCycling ‘74 Max_
daedalus-mainnetDaedalus Mainnet,
daedalus-testnetDaedalus Testnet,
daisydiskDaisyDisk
dangerzoneDangerzone
darktabledarktable
darwindumperDarwinDumper,
dashDash,
dash-dashDash
dashcam-viewerDashcam Viewer
dashlaneDashlane
datDat Desktop
data-integrationPentaho Data Integration
data-rescueData Rescue 6,
data-science-studioDataiku Data Science Studio
datadog-agentDatadog Agent
datagraphDataGraph,
datagripDataGrip,
datazenitDatazenit
datovkaDatovka
datweatherdoeDatWeatherDoe
davmailDavMail
day-oDay-O
db-browser-for-sqliteDB Browser for SQLite
dbeaver-communityDBeaver Community Edition
dbeaver-enterpriseDBeaver Enterprise Edition
dbglassDBGlassbeta.6
dbkodadbKoda
dbnginDBngin,42
dbschemaDbSchema
dbvisualizerDbVisualizer
dcommanderDCommander
dcp-o-maticDCP-o-matic
dcp-o-matic-batch-converterDCP-o-matic Batch converter
dcp-o-matic-encode-serverDCP-o-matic Encode Server
dcp-o-matic-kdm-creatorDCP-o-matic KDM Creator
dcp-o-matic-playerDCP-o-matic Player
dcv-viewerNICE DCV Viewer
dd-utilitydd Utility
ddnetDDNet
deadboltDeadbolt
deathtodsstoreDeathToDSStore
debookeeDebookee,
decksetDeckset,
declonerDecloner,23
decoDeco
decreditonDecrediton
deeperDeeper
deepgitDeepGit
deeplDeepL
deepnestDeepnest
deepstreamdeepstream
deezerDeezer
default-folder-xDefault Folder X,
defoldDefold
dejaluDejaLu,
delayedlauncherDelayedLauncher
delicious-libraryDelicious Library
deltachatDeltaChat
deltawalkerDeltaWalker
delugeDeluge
dendroscopeDendroscope
denemoDenemo
depthmapxdepthmapX
deskreenDeskreen
desktopprdesktoppr
desktoputilityDesktopUtility
desmumeDeSmuME
detectx-swiftDetectX Swift
detexifyDetexify
devbookDevbook
devdocsDevDocs App
developerexcusesDeveloper Excuses Screensaver
deviceinfoDeviceInfo
devilutionxDevilutionX
devkinstaDevKinsta
devolo-cockpitDevolo dLAN Cockpit
devonagentDEVONagent Pro
devonthinkDEVONthink
devutilsDevUtils,99
dexedDexed
dhsDylib Hijack Scanner
diaDia,7
diagnosticsDiagnostics
dialpadDialpad
diashapesDia
dictaterDictater
dictcc-en-de-dictionary-pluginstorycall.us English-German dictionary plugin
dictionariesDictionaries,
dictunifierDictUnifier
diffforkDiffFork
diffmergeDiffMerge
digikamdigiKam
digitalDigital
dingtalkDingTalk
dingtalk-liteDingTalk Lite
discordDiscord
discretescrollDiscreteScroll
disk-arbitratorDisk Arbitrator
disk-dietDisk Diet,
disk-drillDisk Drill
disk-expertDisk Expert,
disk-inventory-xDisk Inventory X
diskcatalogmakerDiskCatalogMaker
diskmaker-xDiskMaker X
diskwaveDiskWave
displapertureDisplaperture,
displaycalDisplayCAL
displaysDisplays,
dittoDitto,
divvyDivvy,
djl-benchdjl-bench
djvDJV Imaging
djviewDjView,3
dmenu-macdmenu-mac
dmidiplayerdmidiplayer
dmm-playerDMM Player
dmm-player-for-chromeDMM Player for Chrome
do-not-disturbDo Not Disturb
dockerDocker Desktop,
docker-toolboxDocker Toolbox
dockeydockeylatest
dockmateDock Mate,
dockstationDockStation
dockviewdockview,
dogecoinDogecoin
dolphinDolphin
domainbrainDomainBrain
doomrlDoom the Roguelike
doomsday-engineDoomsday Engine
dosboxDOSBox,3
dosbox-xDOSBox-X,
doteditorDotEditor
dotnet.Net Runtime,03e
dotnet-sdk.NET SDK,14acc
double-commanderDouble Commander
doubletwistdoubleTwist,
downieDownie,
doxieDoxie
doxygenDoxygen
dozerDozer
dramaDrama,43
drawbotDrawBot
drawiostorycall.us Desktop
dremel-slicerDremel DigiLab 3D Slicer
drivedxDriveDX,
drivethrurpgDriveThruRPG Library App
droididDroidID,7
drop-to-gifDrop to GIF
dropboxDropbox
dropbox-captureDropbox Capture
dropbox-passwordsDropbox Passwords
dropdmgDropDMG
dropletmanagerDigitalOcean Droplets Manager
droplrDroplr,
dropshareDropshare,
dropzoneDropzone,
drovioDrovio
dteoh-devdocsDevDocs
duckietvduckieTV
duefocusDueFocus
duetDuet
dungeon-crawl-stone-soup-consoleDungeon Crawl Stone Soup
dungeon-crawl-stone-soup-tilesDungeon Crawl Stone Soup
duo-connectDuoConnect
dupegurudupeGuru
duplicacyDuplicacy
duplicacy-web-editionDuplicacy Web Edition
duplicate-annihilator-for-photosDuplicate Annihilator for Photoslatest
duplicate-file-finderDuplicate File Finder,
duplicatiDuplicati,beta
dupscanubDupScan
dust3dDust3Drc.6
dustyDusty
dvdstylerDVDStyler
dwarf-fortressDwarf Fortress
dwarf-fortress-lmpDwarf Fortress LMP (Lazy Mac Pack)+dfhack-r1
dwgseeDWGSee
dwihn0r-keepassxKeePassX
dyalogDyalog APL
dyn-updaterDyn Updater
dynalistDynalistlatest
dynamic-dark-modeDynamic Dark Mode
dynamodb-localAmazon DynamoDB Locallatest
dynobaseDynobase
eagleAutodesk EAGLE
eaglefilerEagleFiler
ealeksandrov-cd-tocd_to
earsEars,16
easy-move-plus-resizeEasy Move+Resize
easyedaEasyEDA
easyfindEasyFind
easytetherEasyTether16
ebibookreaderstorycall.usader
ebmacEBMac
eclipse-cppEclipse IDE for C/C++ Developers,R
eclipse-dslEclipse IDE for Java and DSL Developers,R
eclipse-ideEclipse IDE for Eclipse Committers,R
eclipse-installerEclipse Installer,R
eclipse-javaEclipse IDE for Java Developers,R
eclipse-javascriptEclipse IDE for JavaScript and Web Developers,R
eclipse-jeeEclipse IDE for Java EE Developers,R
eclipse-modelingEclipse Modeling Tools,R
eclipse-phpEclipse IDE for PHP Developers,R
eclipse-platformEclipse SDK,
eclipse-rcpEclipse for RCP and RAP Developers,R
eclipse-testingEclipse for Testers,R
eddieAir VPN
edenmathEdenMath,8
edex-uieDEX-UI
edfbrowserEDFbrowser,81befb
editaroEditaro
eggplanteggPlant Functional,
eiskaltdcppEiskaltDC++
ejectorEjector
elanELAN
elasticwolfAWS ElasticWolf Client Console
electermelecterm
electorrentElectorrent
electric-sheepElectric Sheep
electricbinaryElectric VLSI Design System
electrocrudElectroCRUD
electronElectron
electron-api-demosElectron API Demos
electron-cashElectron Cash
electron-fiddleElectron Fiddle
electronic-wechatElectronic WeChat
electronmailElectronMail
electrumElectrum
electrum-ltcElectrum-LTC
electrumsvElectrumSVb1
elementElement
elmedia-playerElmedia Player,
eloston-chromiumUngoogled Chromium_x
elpassElpass,
emacsEmacs
emacsclientemacsclient
emailchemyEmailchemy
emby-serverEmby Server
emclienteM Client
emeEME
emojipediaEmojipedia
empocheEmpoche
enclaveEnclave
encryptmeEncryptMe,
encryptrSpiderOak Encryptr
endless-skyEndless Sky
endnoteEndNote
enduranceEndurance,47
energiaEnergiaE23
energybarEnergyBar
enfuseguiEnfuseGUI
engine-primeEngine Prime,5f4b42a70b
enigmaEnigma
enjoyableEnjoyable,
enpassEnpass
entropyEntropy
envkeyEnvKey
enzymexEnzymeX
epicEpic Privacy Browser
epic-gamesEpic Games Launcher
epichromeEpichrome
epilogue-operatorEpilogue Operator
epoccamEpocCam
epoch-flip-clockEpoch Flip Clock Screensaver
epub-to-pdfepubpdf
epubmdimporterEPUB Spotlight
epubquicklookEPUB QuickLook
eqmaceqMac
eset-cyber-security-proESET Cyber Security Pro
espressoEspresso
ethereum-walletEthereum Wallet
etrecheckproEtreCheck
eudicEudic,
euleul
eurkeyEurKEY keyboard layoutlatest
ev3-classroomEV3 Classroom
eve-launcherEve Online
evernoteEvernote,
everwebEverWeb
evkeyEVKey,1
exactscanExactScan
exfalsoEx Falso
exifcleanerExifCleaner
exifrenamerExifRenamer,15
exist-dbeXist-db
exodusExodus
expandriveExpanDrive7,
explorerExplorer
expo-xdeExpo Development Environment (XDE)
expressionsExpressions
expressscribeExpress Scribe Transcription Software
expressvpnExpressVPN
extratermextraterm
f-barF-Bar
fabfilter-microFabFilter Micro
fabfilter-oneFabFilter One
fabfilter-pro-cFabFilter Pro-C
fabfilter-pro-dsFabFilter Pro-DS
fabfilter-pro-gFabFilter Pro-G
fabfilter-pro-lFabFilter Pro-L
fabfilter-pro-mbFabFilter Pro-MB
fabfilter-pro-qFabFilter Pro-Q
fabfilter-pro-rFabFilter Pro-R
fabfilter-saturnFabFilter Saturn
fabfilter-simplonFabFilter Simplon
fabfilter-timelessFabFilter Timeless
fabfilter-twinFabFilter Twin
fabfilter-volcanoFabFilter Volcano
factorFactor
fakeFake,
falcon-sql-clientFalcon SQL Client
fannyFannyWidget
fantasticalFantastical,
fantasy-groundsFantasy Groundslatest
fantasy-map-generatorAzgaar's Fantasy Map Generator
far2lfar2lb,
farragoFarrago
fastclickerFastClicker
fastonosqlFastoNoSQL
fastrawviewerFastRawViewer
fastscriptsFastScripts,
fauxpasFaux Pas
favroFavro
fawkesFawkes
faxbotFaxbot,
fbreaderFBReader
fedora-media-writerFedora Media Writer
feed-the-beastFeed the Beast,fccf31
feemFeem
feishufeishu,28b
fellowFellow
fenixFenix
ferdiFerdi
fetchFetch,
ff-worksff·Works
figfig,
figmaFigma
figmadaemonFigma Font Installers20
figtreeFigTree
fijiFiji
file-juicerFile Juicer
filebotFileBot
filemaker-proFileMaker Pro
filemonFile Monitorlatest
filepaneFilePane,
final-cut-library-managerArctic Whiteness Final Cut Library Manager
final-fantasy-xiv-onlineFinal Fantasy XIVpnvdkzgk77dj10
find-any-fileFind Any File
find-empty-foldersFind Empty Folders
findergoFinderGo
finereaderABBYY FineReader Pro,
fingFing Desktop
fing-cliFing Desktop Embedded CLI
finickyFinicky
finisher-voodooFinisher VOODOO
firealpacaFire Alpacalatest
firebase-adminFirebase Admin
firebird-emufirebird
firecampFirecamp
fireflyFirefly
firefoxMozilla Firefox
firestormPhoenix Firestorm viewer for Second Life
firestormosPhoenix Firestorm viewer for OpenSim
fireworksFireworks
firmaecFirmaEC
fiscriptFiScript
fissionFission
fitbit-os-simulatorFitbit OS Simulator
fl-studioFL Studio
flaconFlacon
flameFlame
flameshotFlameshot
flash-decompiler-trillixFlash Decompiler Trillix
fldigifldigi
flexiglassFlexiglass,
flicFlic
flickr-uploadrFlickr Uploadr,
flightgearFlightGear
flip4macFlip4Mac
flipperFacebook Flipper
fliqloFliqlo
flircFlirc
flixtoolsOpenSubtitles FlixTools Lite
flockFlock
flomoflomo
flotatoFlotato36,1
flowFlow
flowdockFlowdock,35
flowsyncPolar FlowSync Software
flrigflrig
fluent-readerFluent Reader
fluidFluid,
flumeFlume
fluorFluor
flutterFlutter SDK
fluxstorycall.us
flvcd-bigrats硕鼠MAC
flyfly
flycutFlycut
flying-carpetFlying Carpet
fmailFMail,92
fmanfman
fmeFME Desktop,
focusFocus
focus-boosterFocus Booster
focusatwillFocus@Will
focusedFocused,
focuswriterFocusWriter
fogFog
folding-at-homeFolding@home
foldingtextFoldingText,
folditFolditlatest
folxFolx,
font-smoothing-adjusterFont Smoothing Adjuster
fontbaseFontBase
fontexplorer-x-proFontExplorer X Pro
fontforgeFontForge,21ad4a1
fontgogglesFontGoggles
fontlabFontlab
fontplopFontplop
fontstandFontstand
foobarfoobar
force-pasteForce Paste
forecastForecast,
forkFork
forkliftForkLift,
forticlientFortiClient
forticlient-vpnFortiClient VPN
fotokastenFotokasten,
foxglove-studioFoxglove Studio
foxitreaderFoxit Reader
foxmailFoxmail
fpc-lazPascal compiler for Lazarus,
fpc-src-lazPascal compiler source files for Lazarus,
framerFramer
framer-xFramer X,
franzFranz
freacfre:ac
fredm-fuseFuse for Mac OS X
free-download-managerFree Download Manager
free-rulerFree Ruler
freebinaryFree42 Binary
freedecimalFree42 Decimal
freecadFreeCAD,
freecolFreeCol
freedomFreedom,
freedomeF-Secure Freedome
freemindFreeMind
freenettrayFreenet
freeorionFreeOrion,f
freeplaneFreeplane
freesmug-chromiumChromium
freesurferFreeSurferlatest
freeterFreeter
freetubeFreeTube
freeyourmusicFreeYourMusic
freezeFreeze,
frescobaldiFrescobaldi
frhelperFrhelper,
fromscratchFromScratch
frontFront
fs-uaeFS-UAE
fs-uae-launcherFS-UAE Launcher
fsmonitorFSMonitor,
fsnotesFSNotes
fspyfSpy
fstreamFStream,
fuguFugupre1
functionflipFunctionFlip
funterFunter,
fuseFuse Studio
futubullFutubull,
futurerestore-guiFutureRestore GUI
fuwariFuwari
fuzzyclockFuzzyClock,
fvimFVim,g98c
g-desktop-suiteG Desktop Suite
gactionsgactions3
gamerangerGameRanger
ganacheGanache
ganttprojectGanttProject
garagebuyGarageBuy
garagesaleGarageSale
gargoyleGargoyle
gas-maskGas Mask
gatherGather Town
gb-studioGB Studio
gcc-arm-embeddedGCC ARM Embedded
gcollazo-mongodbMongoDBbuild.3
gcsgcs
gdatGenealogical DNA Analysis Toolr08
gdiskGPT fdisk
gdlauncherGDLauncher
geanyGeany,3
gearboyGearboy
gearsystemGearsystem
geburtstagscheckerGeburtstagsChecker,
geekbenchGeekbench,
geektoolGeekTool,
geminiGemini,
geneious-primeGeneious Prime
genymotionGenymotion
geogebraGeoGebra
geomapGeoMapApp
geotagGeoTag
geotag-photos-proGeotag Photos Pro
gephGeph
gephiGephi
get-backup-proGet Backup Pro 3,
get-iplayer-automatorGet iPlayer Automator,
get-lyricalGet Lyrical
getrasplexRasplex Installer
gfxcardstatusgfxCardStatus,
ghdlghdllatest
ghidraGhidra,
ghost-browserGhost Browser
ghosttileKernelpanic GhostTile15,
gifcaptureGifCapture
gifoxgifox,
gifrocketGifrocket
gimpGIMP
gingkoGingko
gistoGisto
git-itGit-it
gitaheadGitAhead
gitbladeGitBlade
gitbookGitBook
gitdockGitDock
giteeGitee
giteyeCollabNet GitEye
gitfiendGitFiend
gitfinderGitFinder,
gitfoxGitfox,
githubGitHub Desktop
githubpulseGithubPulse,
gitifyGitify
gitkrakenGitKraken
gitnotegitnote
gitpigeonGitPigeon
gitscoutGitscoutrc.3,1c55c97
gitterGitter
gitupGitUp
gitxGitX
glanceGlance
glimmerblockerGlimmerBlocker
gloomhaven-helperGloomhaven Helper
gltfquicklookGLTFQuickLook
gluemotionGlueMotion,
glyphfinderGlyphfinder
glyphsGlyphs,
gmail-notifierGmail Notifier
gmvaultGmvault
gns3GNS3
gnucashGnuCash
go-agentGo Agent,
go-serverGo Server,
go2shellGo2Shell,25
go64Go64,
gobdokumenteGoBDokumente
godotGodot Engine
godot-monoGodot Engine
gog-galaxyGOG Galaxya
gogsGo Git Service
golandGoland,
goldencheetahGoldenCheetah
goldendictGoldenDictRC2
goldenpassportGoldenPassport
gollyGolly
goneovimGoneovim
goodsyncGoodSync
goofyGoofy
google-ads-editorGoogle Ads Editorlatest
google-analytics-opt-outGoogle Analytics Opt Out
google-assistantGoogle Assistant Unofficial Desktop Client
google-chatChat
google-chat-electrongoogle-chat-electron
google-chromeGoogle Chrome
google-cloud-sdkGoogle Cloud SDKlatest
google-driveGoogle Drive
google-drive-file-streamGoogle Drive File Stream
google-earth-proGoogle Earth Pro
google-featured-photosGoogle Featured Photos
google-japanese-imeGoogle Japanese Input Method Editorlatest
google-trendsGoogle Trends Screensaverlatest
google-web-designerGoogle Web Designer
googleappengineGoogle App Engine
gopandaGoPanda
gopass-uiGopass UI
gosignGoSign Desktop
gotiengvietGoTiengViet,30
gotomeetingGoToMeeting
gpg-suiteGPG Suite
gpg-suite-no-mailGPG Suite (without GPG Mail)
gpg-suite-pinentryGPG Suite Pinentry
gpg-syncGPG Sync
gplatesGPlates
gpoddergPodder
gpowerG*Power
gps4camgps4cam
gpxseeGPXSee
gqrxGqrx
gradsGrid Analysis and Display System
grafxGrafX2,67
grammarlyGrammarly
grampsGramps,5
grandperspectiveGrandPerspective
grandtotalGrandTotal
graphicconverterGraphicConverter,
graphiqlGraphiQL App
graphql-ideGraphQL IDE
graphql-playgroundGraphQL Playground
graphsketcherGraphSketcher_test_46
grayGray
greenfootGreenfoot
gretlgretld
gridGrid
grid-clockGrid Clock Screensaver
grideaGridea
gridsGrids
grisbiGrisbi
growlnotifyGrowlNotify
gswitchgSwitch
gtkwaveGTKWave
guijsguijs
guild-wars2Guild Wars 2
guildedGuilded
guitar-proGuitar Pro
gulpgulp-app
guppyGuppy
gureumkim구름 입력기
gyazmailGyazMail
gyazoNota Gyazo GIF
gzdoomGZDoom
ha-menuHA Menu
hacker-menuHacker Menu
hackintoolHackintool
hackmdHackMD
hakunekoHakuNeko
hammerspoonHammerspoon
hancockHancock
hancom-wordHacom Word Processor VPlatest
handbrakeHandBrake
handbrakebatchHandBrakeBatch
handshakerHandShaker,
happygrephappygrep
happymacHappyMac
haptic-touch-barHaptic Touch Bar,
haptickeyHapticKey
harborHarbor
harmonyHarmony
haroopadHaroopad
harvestHarvest,
hashbackuphashbackup
hazelHazel
hazeoverHazeOver,
hbuilderxHBuilderX
hdrmergeHDRMerge
headsetHeadset
heavenHeaven Benchmark
hedgewarsHedgewars
heimdall-suiteHeimdall Suite
heliumHelium
heloHELO
hermesHermes,
hermit-crabHermit Crab
hex-fiendHex Fiend
heyHEY
hfsleuthHFSleuthlatest
hiarcs-chess-explorer(Deep) HIARCS Chess Explorer
hiddenbarHidden Bar
hightopHighTop
historyhoundHistoryHound,
hma-pro-vpnHMA! Pro VPNlatest
hocus-focusHocus Focus,
holavpnHola VPN,
home-assistantHome Assistant,
home-inventoryHome Inventory,
honerHoner
hontohonto view app,
hookHook,
hookshotHookshot,53
hopper-debugger-serverHopper Debugger Server
horndisHoRNDIS
horosHoros – Free, open medical image viewer
hoststoolHosts tool for Mac
hotHot
hotswitchHotSwitch
houdahspotHoudahSpot,
housepartyHouseparty,
hp-eprintHP ePrint
hp-primeHP Prime_01_16
hstrackerHearthstone Deck Tracker
http-toolkitHTTP Toolkit
hubstaffHubstaff,
hue-topiaHue-topia,
huginHugin
hushHush
hwsensorsHWSensors
hydrogenHydrogen
hydrus-networkhydrus-network
hypeTumult Hype,
hyperHyper
hyperbackupexplorerHyperBackupExplorer
hyperdockHyperDocklatest
hyperkeyhyperkey
hyperswitchHyperSwitchdev
i1profileri1Profiler
ibabeliBabel
ibackupiBackup
ibackup-vieweriBackup Viewer
ibackupbotiBackupBot
ibetterchargeiBetterCharge,
ibm-aspera-connectIBM Aspera Connect
ibm-cloud-cliIBM Cloud CLI
iborediBored
icabiCab
icanhazshortcutiCanHazShortcut
iccInternational Chess Club,
icebergIceberg
icefloorIceFloor
icestudioicestudio
icloud-controliCloud Control
icollectionsiCollections,
iconizerIconizer
iconjarIconJar,
iconsIcons
icons8Icons8 App,
iconscoutIconscout
iconsetIconset
icqICQ
id3-editorID3 Editor
idafreeIDA Free
idagioIDAGIO
idefragiDefrag
idisplayiDisplaylatest
idriveiDrivelatest
ieasemusicieaseMusic
iexploreriExplorer,
ifunboxiFunBox
igdmIG:dm
igetteriGetter
iglanceiGlance
igvIntegrative Genomics Viewer (IGV)
iinaIINA,
iina-plusIINA+,
ilok-license-manageriLok License Manager,
ilspyILSpyrc2
ilya-birman-typography-layoutIlya Birman Typography Layout
image-toolImage Tool
image2iconImage2Icon,
imagealphaImageAlpha
imagejImageJ
imageminimagemin
imageoptimImageOptim
imazingiMazing,
imdoneimdone
imgotv芒果TV
immersedImmersed,
imoImo Messanger
impactorImpactor
inav-configuratorINAV Configurator
inboardInboard,
indigoIndigo Domotics
infinityInfinity
infoflowBaidu Hi,
informInform6M62
infrainfra
inkdropInkdrop
inkscapeInkscape
inkyInky
inloop-qlplaygroundinloop-qlplayground
insoinso
insomniaInsomnia
inssiderinSSIDer,8
install-disk-creatorInstall Disk Creator
instatus-outInstatus Out
insyncInsync
integrityIntegrity
intel-haxmIntel HAXM
intel-power-gadgetIntel Power Gadget,b7b1b3e1dffd9b20
intel-psxe-ce-c-plus-plusIntel Parallel Studio XE Composer Edition for C++,
intellidockIntelliDock
intellij-ideaIntelliJ IDEA Ultimate,
intellij-idea-ceIntelliJ IDEA Community Edition,
interarchyInterarchy
internxt-driveInternxt Drive
intune-company-portalCompany Portal
invesaliusInVesalius
invisiblixinvisibliX
invisionsyncInVision Sync,
invisor-liteInvisor Lite,
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FIGURE 1: Three types of cryptography: secret key, public key, and hash function.

Secret Key Cryptography

Secret key cryptography methods employ a single key for both encryption and decryption. As shown in Figure 1A, the sender uses the key to encrypt the plaintext and sends the ciphertext to the receiver. The receiver applies the same key to decrypt the message and recover the plaintext. Because a single key is used for both functions, secret key cryptography is also called symmetric encryption.

With this form of cryptography, it is obvious that the key must be known to both the sender and the receiver; that, in fact, is the secret. The biggest difficulty with this approach, of course, is the distribution of the key (more on that later in the discussion of public key cryptography).

Secret key cryptography schemes are generally categorized as being either stream ciphers or block ciphers.

A) Self-synchronizing stream cipher. (From Schneier, , Figure )

B) Synchronous stream cipher. (From Schneier, , Figure )

FIGURE 2: Types of stream ciphers.

Stream ciphers operate on a single bit (byte or computer word) at a time and implement some form of feedback mechanism so that the key is constantly changing. Stream ciphers come in several flavors but two are worth mentioning here (Figure 2). Self-synchronizing stream ciphers calculate each bit in the keystream as a function of the previous n bits in the keystream. It is termed "self-synchronizing" because the decryption process can stay synchronized with the encryption process merely by knowing how far into the n-bit keystream it is. One problem is error propagation; a garbled bit in transmission will result in n garbled bits at the receiving side. Synchronous stream ciphers generate the keystream in a fashion independent of the message stream but by using the same keystream generation function at sender and receiver. While stream ciphers do not propagate transmission errors, they are, by their nature, periodic so that the keystream will eventually repeat.

FIGURE 3: Feistel cipher. (Source: Wikimedia Commons)

A block cipher is so-called because the scheme encrypts one fixed-size block of data at a time. In a block cipher, a given plaintext block will always encrypt to the same ciphertext when using the same key (i.e., it is deterministic) whereas the same plaintext will encrypt to different ciphertext in a stream cipher. The most common construct for block encryption algorithms is the Feistel cipher, named for cryptographer Horst Feistel (IBM). As shown in Figure 3, a Feistel cipher combines elements of substitution, permutation (transposition), and key expansion; these features create a large amount of "confusion and diffusion" (per Claude Shannon) in the cipher. One advantage of the Feistel design is that the encryption and decryption stages are similar, sometimes identical, requiring only a reversal of the key operation, thus dramatically reducing the size of the code or circuitry necessary to implement the cipher in software or hardware, respectively. One of Feistel's early papers describing this operation is "Cryptography and Computer Privacy" (Scientific American, May , (5), ).

Block ciphers can operate in one of several modes; the following are the most important:

  • Electronic Codebook (ECB) mode is the simplest, most obvious application: the secret key is used to encrypt the plaintext block to form a ciphertext block. Two identical plaintext blocks, then, will always generate the same ciphertext block. ECB is susceptible to a variety of brute-force attacks (because of the fact that the same plaintext block will always encrypt to the same ciphertext), as well as deletion and insertion attacks. In addition, a single bit error in the transmission of the ciphertext results in an error in the entire block of decrypted plaintext.
  • Cipher Block Chaining (CBC) mode adds a feedback mechanism to the encryption scheme; the plaintext is exclusively-ORed (XORed) with the previous ciphertext block prior to encryption so that two identical plaintext blocks will encrypt differently. While CBC protects against many brute-force, deletion, and insertion attacks, a single bit error in the ciphertext yields an entire block error in the decrypted plaintext block and a bit error in the next decrypted plaintext block.
  • Cipher Feedback (CFB) mode is a block cipher implementation as a self-synchronizing stream cipher. CFB mode allows data to be encrypted in units smaller than the block size, which might be useful in some applications such as encrypting interactive terminal input. If we were using one-byte CFB mode, for example, each incoming character is placed into a shift register the same size as the block, encrypted, and the block transmitted. At the receiving side, the ciphertext is decrypted and the extra bits in the block (i.e., everything above and beyond the one byte) are discarded. CFB mode generates a keystream based upon the previous ciphertext (the initial key comes from an Initialization Vector [IV]). In this mode, a single bit error in the ciphertext affects both this block and the following one.
  • Output Feedback (OFB) mode is a block cipher implementation conceptually similar to a synchronous stream cipher. OFB prevents the same plaintext block from generating the same ciphertext block by using an internal feedback mechanism that generates the keystream independently of both the plaintext and ciphertext bitstreams. In OFB, a single bit error in ciphertext yields a single bit error in the decrypted plaintext.
  • Counter (CTR) mode is a relatively modern addition to block ciphers. Like CFB and OFB, CTR mode operates on the blocks as in a stream cipher; like ECB, CTR mode operates on the blocks independently. Unlike ECB, however, CTR uses different key inputs to different blocks so that two identical blocks of plaintext will not result in the same ciphertext. Finally, each block of ciphertext has specific location within the encrypted message. CTR mode, then, allows blocks to be processed in parallel &#; thus offering performance advantages when parallel processing and multiple processors are available &#; but is not susceptible to ECB's brute-force, deletion, and insertion attacks.

A good overview of these different modes can be found at CRYPTO-IT.

Secret key cryptography algorithms in use today &#; or, at least, important today even if not in use &#; include:

  • Data Encryption Standard (DES): One of the most well-known and well-studied SKC schemes, DES was designed by IBM in the s and adopted by the National Bureau of Standards (NBS) [now the National Institute of Standards and Technology (NIST)] in for commercial and unclassified government applications. DES is a Feistel block-cipher employing a bit key that operates on bit blocks. DES has a complex set of rules and transformations that were designed specifically to yield fast hardware implementations and slow software implementations, although this latter point is not significant today since the speed of computer processors is several orders of magnitude faster today than even twenty years ago. DES was based somewhat on an earlier cipher from Feistel called Lucifer which, some sources report, had a bit key. This was rejected, partially in order to fit the algorithm onto a single chip and partially because of the National Security Agency (NSA). The NSA also proposed a number of tweaks to DES that many thought were introduced in order to weaken the cipher; analysis in the s, however, showed that the NSA suggestions actually strengthened DES, including the removal of a mathematical back door by a change to the design of the S-box (see "The Legacy of DES" by Bruce Schneier []). In April , the NSA declassified a fascinating historical paper titled "NSA Comes Out of the Closet: The Debate over Public Cryptography in the Inman Era" that appeared in Cryptologic Quarterly, Spring

    DES was defined in American National Standard X and three Federal Information Processing Standards (FIPS), all withdrawn in

    • FIPS PUB DES (Archived file)
    • FIPS PUB Guidelines for Implementing and Using the NBS Data Encryption Standard
    • FIPS PUB DES Modes of Operation

    Information about vulnerabilities of DES can be obtained from the Electronic Frontier Foundation.

    Two important variants that strengthen DES are:

    • Triple-DES (3DES): A variant of DES that employs up to three bit keys and makes three encryption/decryption passes over the block; 3DES is also described in FIPS PUB and was an interim replacement to DES in the lates and earlys.

    • DESX: A variant devised by Ron Rivest. By combining 64 additional key bits to the plaintext prior to encryption, effectively increases the keylength to bits.

    More detail about DES, 3DES, and DESX can be found below in Section

  • Advanced Encryption Standard (AES): In , NIST initiated a very public, /2 year process to develop a new secure cryptosystem for U.S. government applications (as opposed to the very closed process in the adoption of DES 25 years earlier). The result, the Advanced Encryption Standard, became the official successor to DES in December AES uses an SKC scheme called Rijndael, a block cipher designed by Belgian cryptographers Joan Daemen and Vincent Rijmen. The algorithm can use a variable block length and key length; the latest specification allowed any combination of keys lengths of , , or bits and blocks of length , , or bits. NIST initially selected Rijndael in October and formal adoption as the AES standard came in December FIPS PUB describes a bit block cipher employing a , , or bit key. AES is also part of the NESSIE approved suite of protocols. (See also the entries for CRYPTEC and NESSIE Projects in Table 3.)

    The AES process and Rijndael algorithm are described in more detail below in Section

  • CAST/ CAST (aka CAST5), described in Request for Comments (RFC) , is a DES-like substitution-permutation crypto algorithm, employing a bit key operating on a bit block. CAST (aka CAST6), described in RFC , is an extension of CAST, using a bit block size and a variable length (, , , , or bit) key. CAST is named for its developers, Carlisle Adams and Stafford Tavares, and is available internationally. CAST was one of the Round 1 algorithms in the AES process.

  • International Data Encryption Algorithm (IDEA): Secret-key cryptosystem written by Xuejia Lai and James Massey, in and patented by Ascom; a bit SKC block cipher using a bit key.

  • Rivest Ciphers (aka Ron's Code): Named for Ron Rivest, a series of SKC algorithms.

    • RC1: Designed on paper but never implemented.

    • RC2: A bit block cipher using variable-sized keys designed to replace DES. It's code has not been made public although many companies have licensed RC2 for use in their products. Described in RFC

    • RC3: Found to be breakable during development.

    • RC4: A stream cipher using variable-sized keys; it is widely used in commercial cryptography products. An update to RC4, called Spritz (see also this article), was designed by Rivest and Jacob Schuldt. More detail about RC4 (and a little about Spritz) can be found below in Section

    • RC5: A block-cipher supporting a variety of block sizes (32, 64, or bits), key sizes, and number of encryption passes over the data. Described in RFC

    • RC6: A bit block cipher based upon, and an improvement over, RC5; RC6 was one of the AES Round 2 algorithms.

  • Blowfish: A symmetric bit block cipher invented by Bruce Schneier; optimized for bit processors with large data caches, it is significantly faster than DES on a Pentium/PowerPC-class machine. Key lengths can vary from 32 to bits in length. Blowfish, available freely and intended as a substitute for DES or IDEA, is in use in a large number of products.

  • Twofish: A bit block cipher using , , or bit keys. Designed to be highly secure and highly flexible, well-suited for large microprocessors, 8-bit smart card microprocessors, and dedicated hardware. Designed by a team led by Bruce Schneier and was one of the Round 2 algorithms in the AES process.

  • Threefish: A large block cipher, supporting , , and bit blocks and a key size that matches the block size; by design, the block/key size can grow in increments of bits. Threefish only uses XOR operations, addition, and rotations of bit words; the design philosophy is that an algorithm employing many computationally simple rounds is more secure than one employing highly complex &#; albeit fewer &#; rounds. The specification for Threefish is part of the Skein Hash Function Family documentation.

  • Anubis: Anubis is a block cipher, co-designed by Vincent Rijmen who was one of the designers of Rijndael. Anubis is a block cipher, performing substitution-permutation operations on bit blocks and employing keys of length to bits (in bit increments). Anubis works very much like Rijndael. Although submitted to the NESSIE project, it did not make the final cut for inclusion.

  • ARIA: A bit block cipher employing , , and bit keys to encrypt bit blocks in 12, 14, and 16 rounds, depending on the key size. Developed by large group of researchers from academic institutions, research institutes, and federal agencies in South Korea in , and subsequently named a national standard. Described in RFC

  • Camellia: A secret-key, block-cipher crypto algorithm developed jointly by Nippon Telegraph and Telephone (NTT) Corp. and Mitsubishi Electric Corporation (MEC) in Camellia has some characteristics in common with AES: a bit block size, support for , , and bit key lengths, and suitability for both software and hardware implementations on common bit processors as well as 8-bit processors (e.g., smart cards, cryptographic hardware, and embedded systems). Also described in RFC Camellia's application in IPsec is described in RFC and application in OpenPGP in RFC Camellia is part of the NESSIE suite of protocols.

  • CLEFIA: Described in RFC , CLEFIA is a bit block cipher employing key lengths of , , and bits (which is compatible with AES). The CLEFIA algorithm was first published in by Sony Corporation. CLEFIA is one of the new-generation lightweight blockcipher algorithms designed after AES, offering high performance in software and hardware as well as a lightweight implementation in hardware.

  • FFX-A2 and FFX-A10: FFX (Format-preserving, Feistel-based encryption) is a type of Format Preserving Encryption (FPE) scheme that is designed so that the ciphertext has the same format as the plaintext. FPE schemes are used for such purposes as encrypting social security numbers, credit card numbers, limited size protocol traffic, etc.; this means that an encrypted social security number, for example, would still be a nine-digit string. FFX can theoretically encrypt strings of arbitrary length, although it is intended for message sizes smaller than that of AES (2 points). The FFX version specification describes FFX-A2 and FFX-A10, which are intended for bit binary strings or digit decimal strings.

  • GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile) encryption: GSM mobile phone systems use several stream ciphers for over-the-air communication privacy. A5/1 was developed in for use in Europe and the U.S. A5/2, developed in , is a weaker algorithm and intended for use outside of Europe and the U.S. Significant flaws were found in both ciphers after the "secret" specifications were leaked in , however, and A5/2 has been withdrawn from use. The newest version, A5/3, employs the KASUMI block cipher. NOTE: Unfortunately, although A5/1 has been repeatedly "broken" (e.g., see "Secret code protecting cellphone calls set loose" [] and "Cellphone snooping now easier and cheaper than ever" []), this encryption scheme remains in widespread use, even in 3G and 4G mobile phone networks. Use of this scheme is reportedly one of the reasons that the National Security Agency (NSA) can easily decode voice and data calls over mobile phone networks.

  • GPRS (General Packet Radio Service) encryption: GSM mobile phone systems use GPRS for data applications, and GPRS uses a number of encryption methods, offering different levels of data protection. GEA/0 offers no encryption at all. GEA/1 and GEA/2 are proprietary stream ciphers, employing a bit key and a bit or bit state, respectively. GEA/1 and GEA/2 are most widely used by network service providers today although both have been reportedly broken. GEA/3 is a bit block cipher employing a bit key that is used by some carriers; GEA/4 is a bit clock cipher with a bit key, but is not yet deployed.

  • KASUMI: A block cipher using a bit key that is part of the Third-Generation Partnership Project (3gpp), formerly known as the Universal Mobile Telecommunications System (UMTS). KASUMI is the intended confidentiality and integrity algorithm for both message content and signaling data for emerging mobile communications systems.

  • KCipher Described in RFC , KCipher-2 is a stream cipher with a bit key and a bit initialization vector. Using simple arithmetic operations, the algorithms offers fast encryption and decryption by use of efficient implementations. KCipher-2 has been used for industrial applications, especially for mobile health monitoring and diagnostic services in Japan.

  • KHAZAD:KHAZAD is a so-called legacy block cipher, operating on bit blocks à la older block ciphers such as DES and IDEA. KHAZAD uses eight rounds of substitution and permutation, with a bit key.

  • KLEIN: Designed in , KLEIN is a lightweight, bit block cipher supporting , and bit keys. KLEIN is designed for highly resource constrained devices such as wireless sensors and RFID tags.

  • Light Encryption Device (LED): Designed in , LED is a lightweight, bit block cipher supporting and bit keys. LED is designed for RFID tags, sensor networks, and other applications with devices constrained by memory or compute power.

  • MARS:MARS is a block cipher developed by IBM and was one of the five finalists in the AES development process. MARS employs bit blocks and a variable key length from to bits. The MARS document stresses the ability of the algorithm's design for high speed, high security, and the ability to efficiently and effectively implement the scheme on a wide range of computing devices.

  • MISTY1: Developed at Mitsubishi Electric Corp., a block cipher using a bit key and bit blocks, and a variable number of rounds. Designed for hardware and software implementations, and is resistant to differential and linear cryptanalysis. Described in RFC , MISTY1 is part of the NESSIE suite.

  • Salsa and ChaCha: Salsa20 is a stream cipher proposed for the eSTREAM project by Daniel Bernstein. Salsa20 uses a pseudorandom function based on bit (whole word) addition, bitwise addition (XOR), and rotation operations, aka add-rotate-xor (ARX) operations. Salsa20 uses a bit key although a bit key variant also exists. In , Bernstein published ChaCha, a new family of ciphers related to Salsa ChaCha20, originally defined in RFC (now obsoleted), is employed (with the Poly authenticator) in Internet Engineering Task Force (IETF) protocols, most notably for IPsec and Internet Key Exchange (IKE), per RFC , and Transaction Layer Security (TLS), per RFC In , Google adopted ChaCha20/Poly for use in OpenSSL, and they are also a part of OpenSSH. RFC replaces RFC , and provides an implementation guide for both the ChaCha20 cipher and Poly message authentication code, as well as the combined CHACHAPOLY Authenticated-Encryption with Associated-Data (AEAD) algorithm.

  • Secure and Fast Encryption Routine (SAFER): A series of block ciphers designed by James Massey for implementation in software and employing a bit block. SAFER K, published in , used a bit key and SAFER K, published in , employed a bit key. After weaknesses were found, new versions were released called SAFER SK, SK, and SK, using , , and bit keys, respectively. SAFER+ () used a bit block and was an unsuccessful candidate for the AES project; SAFER++ () was submitted to the NESSIE project.

  • SEED: A block cipher using bit blocks and bit keys. Developed by the Korea Information Security Agency (KISA) and adopted as a national standard encryption algorithm in South Korea. Also described in RFC

  • Serpent:Serpent is another of the AES finalist algorithms. Serpent supports , , or bit keys and a block size of bits, and is a round substitution–permutation network operating on a block of four bit words. The Serpent developers opted for a high security margin in the design of the algorithm; they determined that 16 rounds would be sufficient against known attacks but require 32 rounds in an attempt to future-proof the algorithm.

  • SHACAL: SHACAL is a pair of block ciphers based upon the Secure Hash Algorithm (SHA) and the fact that SHA is, at heart, a compression algorithm. As a hash function, SHA repeatedly calls on a compression scheme to alter the state of the data blocks. While SHA (like other hash functions) is irreversible, the compression function can be used for encryption by maintaining appropriate state information. SHACAL-1 is based upon SHA-1 and uses a bit block size while SHACAL-2 is based upon SHA and employs a bit block size; both support key sizes from to bits. SHACAL-2 is one of the NESSIE block ciphers.

  • Simon and Speck: Simon and Speck are a pair of lightweight block ciphers proposed by the NSA in , designed for highly constrained software or hardware environments. (E.g., per the specification, AES requires gate equivalents and these ciphers require less than ) While both cipher families perform well in both hardware and software, Simon has been optimized for high performance on hardware devices and Speck for performance in software. Both are Feistel ciphers and support ten combinations of block and key size:

  • Skipjack: SKC scheme proposed, along with the Clipper chip, as part of the never-implemented Capstone project. Although the details of the algorithm were never made public, Skipjack was a block cipher using an bit key and 32 iteration cycles per bit block. Capstone, proposed by NIST and the NSA as a standard for public and government use, met with great resistance by the crypto community largely because the design of Skipjack was classified (coupled with the key escrow requirement of the Clipper chip).

  • SM4: Formerly called SMS4, SM4 is a bit block cipher using bit keys and 32 rounds to process a block. Declassified in , SM4 is used in the Chinese National Standard for Wireless Local Area Network (LAN) Authentication and Privacy Infrastructure (WAPI). SM4 had been a proposed cipher for the Institute of Electrical and Electronics Engineers (IEEE) i standard on security mechanisms for wireless LANs, but has yet to be accepted by the IEEE or International Organization for Standardization (ISO). SM4 is described in SMS4 Encryption Algorithm for Wireless Networks (translated by Whitfield Diffie and George Ledin, ) and at the SM4 (cipher) page. SM4 is issued by the Chinese State Cryptographic Authority as GM/T SM4 ().

  • Tiny Encryption Algorithm (TEA): A family of block ciphers developed by Roger Needham and David Wheeler. TEA was originally developed in , and employed a bit key, bit block, and 64 rounds of operation. To correct certain weaknesses in TEA, eXtended TEA (XTEA), aka Block TEA, was released in To correct weaknesses in XTEA and add versatility, Corrected Block TEA (XXTEA) was published in XXTEA also uses a bit key, but block size can be any multiple of bit words (with a minimum block size of 64 bits, or two words) and the number of rounds is a function of the block size (~52+6*words), as shown in Table 1.

  • Block Size
    2n
    Key Size
    mn
    Word Size
    n
    Key Words
    m
    Rounds
    T
    326416432
    4872
    96
    243
    4
    36
    36
    6496
    323
    4
    42
    44
    9696
    482
    3
    52
    54


    642
    3
    4
    68
    69
    72
  • TWINE: Designed by engineers at NEC in , TWINE is a lightweight, bit block cipher supporting and bit keys. TWINE's design goals included maintaining a small footprint in a hardware implementation (i.e., fewer than 2, gate equivalents) and small memory consumption in a software implementation.

Although not an SKC scheme, check out Section about Shamir's Secret Sharing (SSS).

There are several other references that describe interesting algorithms and even SKC codes dating back decades. Two that leap to mind are the Crypto Museum's Crypto List and John J.G. Savard's (albeit old) A Cryptographic Compendium page.

Public Key Cryptography

Public key cryptography has been said to be the most significant new development in cryptography in the last years. Modern PKC was first described publicly by Stanford University professor Martin Hellman and graduate student Whitfield Diffie in Their paper described a two-key crypto system in which two parties could engage in a secure communication over a non-secure communications channel without having to share a secret key.

PKC depends upon the existence of so-called one-way functions, or mathematical functions that are easy to compute whereas their inverse function is relatively difficult to compute. Let me give you two simple examples:

  1. Multiplication vs. factorization: Suppose you have two prime numbers, 3 and 7, and you need to calculate the product; it should take almost no time to calculate that value, which is Now suppose, instead, that you have a number that is a product of two primes, 21, and you need to determine those prime factors. You will eventually come up with the solution but whereas calculating the product took milliseconds, factoring will take longer. The problem becomes much harder if we start with primes that have, say, digits or so, because the product will have ~ digits.
  2. Exponentiation vs. logarithms: Suppose you take the number 3 to the 6th power; again, it is relatively easy to calculate 36 =  But if you start with the number and need to determine the two integers, x and y so that logx  = y, it will take longer to find the two values.

While the examples above are trivial, they do represent two of the functional pairs that are used with PKC; namely, the ease of multiplication and exponentiation versus the relative difficulty of factoring and calculating logarithms, respectively. The mathematical "trick" in PKC is to find a trap door in the one-way function so that the inverse calculation becomes easy given knowledge of some item of information.

Generic PKC employs two keys that are mathematically related although knowledge of one key does not allow someone to easily determine the other key. One key is used to encrypt the plaintext and the other key is used to decrypt the ciphertext. The important point here is that it does not matter which key is applied first, but that both keys are required for the process to work (Figure 1B). Because a pair of keys are required, this approach is also called asymmetric cryptography.

In PKC, one of the keys is designated the public key and may be advertised as widely as the owner wants. The other key is designated the private key and is never revealed to another party. It is straight-forward to send messages under this scheme. Suppose Alice wants to send Bob a message. Alice encrypts some information using Bob's public key; Bob decrypts the ciphertext using his private key. This method could be also used to prove who sent a message; Alice, for example, could encrypt some plaintext with her private key; when Bob decrypts using Alice's public key, he knows that Alice sent the message (authentication) and Alice cannot deny having sent the message (non-repudiation).

Public key cryptography algorithms that are in use today for key exchange or digital signatures include:

  • RSA: The first, and still most common, PKC implementation, named for the three MIT mathematicians who developed it &#; Ronald Rivest, Adi Shamir, and Leonard Adleman. RSA today is used in hundreds of software products and can be used for key exchange, digital signatures, or encryption of small blocks of data. RSA uses a variable size encryption block and a variable size key. The key-pair is derived from a very large number, n, that is the product of two prime numbers chosen according to special rules; these primes may be or more digits in length each, yielding an n with roughly twice as many digits as the prime factors. The public key information includes n and a derivative of one of the factors of n; an attacker cannot determine the prime factors of n (and, therefore, the private key) from this information alone and that is what makes the RSA algorithm so secure. (Some descriptions of PKC erroneously state that RSA's safety is due to the difficulty in factoring large prime numbers. In fact, large prime numbers, like small prime numbers, only have two factors!) The ability for computers to factor large numbers, and therefore attack schemes such as RSA, is rapidly improving and systems today can find the prime factors of numbers with more than digits. Nevertheless, if a large number is created from two prime factors that are roughly the same size, there is no known factorization algorithm that will solve the problem in a reasonable amount of time; a test to factor a digit number took years and over 50 years of compute time. In , Kleinjung et al. reported that factoring a bit (digit) RSA modulus utilizing hundreds of systems took two years and they estimated that a bit RSA modulus would take about a thousand times as long. Even so, they suggested that bit RSA be phased out by (See the Wikipedia article on integer factorization.) Regardless, one presumed protection of RSA is that users can easily increase the key size to always stay ahead of the computer processing curve. As an aside, the patent for RSA expired in September which does not appear to have affected RSA's popularity one way or the other. A detailed example of RSA is presented below in Section

  • Diffie-Hellman: After the RSA algorithm was published, Diffie and Hellman came up with their own algorithm. Diffie-Hellman is used for secret-key key exchange only, and not for authentication or digital signatures. More detail about Diffie-Hellman can be found below in Section

  • Digital Signature Algorithm (DSA): The algorithm specified in NIST's Digital Signature Standard (DSS), provides digital signature capability for the authentication of messages. Described in FIPS PUB

  • ElGamal: Designed by Taher Elgamal, ElGamal is a PKC system similar to Diffie-Hellman and used for key exchange. ElGamal is used in some later version of Pretty Good Privacy (PGP) as well as GNU Privacy Guard (GPG) and other cryptosystems.

  • Elliptic Curve Cryptography (ECC): A PKC algorithm based upon elliptic curves. ECC can offer levels of security with small keys comparable to RSA and other PKC methods. It was designed for devices with limited compute power and/or memory, such as smartcards and PDAs. More detail about ECC can be found below in Section Other references include the Elliptic Curve Cryptography page and the Online ECC Tutorial page, both from Certicom. See also RFC for a review of fundamental ECC algorithms and The Elliptic Curve Digital Signature Algorithm (ECDSA) for details about the use of ECC for digital signatures.

  • Identity-Based Encryption (IBE): IBE is a novel scheme first proposed by Adi Shamir in It is a PKC-based key authentication system where the public key can be derived from some unique information based upon the user's identity, allowing two users to exchange encrypted messages without having an a priori relationship. In , Dan Boneh (Stanford) and Matt Franklin (U.C., Davis) developed a practical implementation of IBE based on elliptic curves and a mathematical construct called the Weil Pairing. In that year, Clifford Cocks (GCHQ) also described another IBE solution based on quadratic residues in composite groups. RFC Identity-Based Cryptography Standard (IBCS) #1 describes an implementation of IBE using Boneh-Franklin (BF) and Boneh-Boyen (BB1) Identity-based Encryption. More detail about Identity-Based Encryption can be found below in Section

  • Public Key Cryptography Standards (PKCS): A set of interoperable standards and guidelines for public key cryptography, designed by RSA Data Security Inc. (These documents are no longer easily available; all links in this section are from storycall.us.)

  • Cramer-Shoup: A public key cryptosystem proposed by R. Cramer and V. Shoup of IBM in

  • Key Exchange Algorithm (KEA): A variation on Diffie-Hellman; proposed as the key exchange method for the NIST/NSA Capstone project.

  • LUC: A public key cryptosystem designed by P.J. Smith and based on Lucas sequences. Can be used for encryption and signatures, using integer factoring.

  • McEliece: A public key cryptosystem based on algebraic coding theory.

For additional information on PKC algorithms, see "Public Key Encryption" (Chapter 8) in Handbook of Applied Cryptography, by A. Menezes, P. van Oorschot, and S. Vanstone (CRC Press, ).


A digression: Who invented PKC? I tried to be careful in the first paragraph of this section to state that Diffie and Hellman "first described publicly" a PKC scheme. Although I have categorized PKC as a two-key system, that has been merely for convenience; the real criteria for a PKC scheme is that it allows two parties to exchange a secret even though the communication with the shared secret might be overheard. There seems to be no question that Diffie and Hellman were first to publish; their method is described in the classic paper, "New Directions in Cryptography," published in the November issue of IEEE Transactions on Information Theory (IT(6), ). As shown in Section , Diffie-Hellman uses the idea that finding logarithms is relatively harder than performing exponentiation. And, indeed, it is the precursor to modern PKC which does employ two keys. Rivest, Shamir, and Adleman described an implementation that extended this idea in their paper, "A Method for Obtaining Digital Signatures and Public Key Cryptosystems," published in the February issue of the Communications of the ACM (CACM), (21(2), ). Their method, of course, is based upon the relative ease of finding the product of two large prime numbers compared to finding the prime factors of a large number.

Diffie and Hellman (and other sources) credit Ralph Merkle with first describing a public key distribution system that allows two parties to share a secret, although it was not a two-key system, per se. A Merkle Puzzle works where Alice creates a large number of encrypted keys, sends them all to Bob so that Bob chooses one at random and then lets Alice know which he has selected. An eavesdropper (Eve) will see all of the keys but can't learn which key Bob has selected (because he has encrypted the response with the chosen key). In this case, Eve's effort to break in is the square of the effort of Bob to choose a key. While this difference may be small it is often sufficient. Merkle apparently took a computer science course at UC Berkeley in and described his method, but had difficulty making people understand it; frustrated, he dropped the course. Meanwhile, he submitted the paper "Secure Communication Over Insecure Channels," which was published in the CACM in April ; Rivest et al.'s paper even makes reference to it. Merkle's method certainly wasn't published first, but he is often credited to have had the idea first.

An interesting question, maybe, but who really knows? For some time, it was a quiet secret that a team at the UK's Government Communications Headquarters (GCHQ) had first developed PKC in the early s. Because of the nature of the work, GCHQ kept the original memos classified. In , however, the GCHQ changed their posture when they realized that there was nothing to gain by continued silence. Documents show that a GCHQ mathematician named James Ellis started research into the key distribution problem in and that by , James Ellis, Clifford Cocks, and Malcolm Williamson had worked out all of the fundamental details of PKC, yet couldn't talk about their work. (They were, of course, barred from challenging the RSA patent!) By , Ellis, Cocks, and Williamson began to get their due credit in a break-through article in WIRED Magazine. And the National Security Agency (NSA) claims to have knowledge of this type of algorithm as early as For some additional insight on who knew what when, see Steve Bellovin's "The Prehistory of Public Key Cryptography."


Hash Functions

Hash functions, also called message digests and one-way encryption, are algorithms that, in essence, use no key (Figure 1C). Instead, a fixed-length hash value is computed based upon the plaintext that makes it impossible for either the contents or length of the plaintext to be recovered. Hash algorithms are typically used to provide a digital fingerprint of a file's contents, often used to ensure that the file has not been altered by an intruder or virus. Hash functions are also commonly employed by many operating systems to encrypt passwords. Hash functions, then, provide a mechanism to ensure the integrity of a file.

Hash functions are also designed so that small changes in the input produce significant differences in the hash value, for example:

Hash string 1: The quick brown fox jumps over the lazy dog
Hash string 2: The quick brown fox jumps over the lazy dog.

MD5 [hash string 1] = 37c4b87edffc5dff5acee7ee09
MD5 [hash string 2] = 0dcde94cfe1d2ae0c8e

SHA1 [hash string 1] = beb5c3c5c1d9bcb2e7cdd76b
SHA1 [hash string 2] = 9c04cde9b11f70cacdce4b

RIPEMD [hash string 1] = eefdda9e2cff
RIPEMD [hash string 2] = 99bacdbe25bbee


Let me reiterate that hashes are one-way encryption. You cannot take a hash and "decrypt" it to find the original string that created it, despite the many web sites that claim or suggest otherwise, such as CrackStation, storycall.us, MD5 Online, md5thiscracker, OnlineHashCrack, and RainbowCrack.

Note that these sites search databases and/or use rainbow tables to find a suitable string that produces the hash in question but one can't definitively guarantee what string originally produced the hash. This is an important distinction. Suppose that you want to crack someone's password, where the hash of the password is stored on the server. Indeed, all you then need is a string that produces the correct hash and you're in! However, you cannot prove that you have discovered the user's password, only a "duplicate key."


Hash algorithms in common use today include:

  • Message Digest (MD) algorithms: A series of byte-oriented algorithms that produce a bit hash value from an arbitrary-length message.

    • MD2 (RFC ): Designed for systems with limited memory, such as smart cards. (MD2 has been relegated to historical status, per RFC )

    • MD4 (RFC ): Developed by Rivest, similar to MD2 but designed specifically for fast processing in software. (MD4 has been relegated to historical status, per RFC )

    • MD5 (RFC ): Also developed by Rivest after potential weaknesses were reported in MD4; this scheme is similar to MD4 but is slower because more manipulation is made to the original data. MD5 has been implemented in a large number of products although several weaknesses in the algorithm were demonstrated by German cryptographer Hans Dobbertin in ("Cryptanalysis of MD5 Compress"). (Updated security considerations for MD5 can be found in RFC )

  • Secure Hash Algorithm (SHA): Algorithm for NIST's Secure Hash Standard (SHS), described in FIPS PUB The status of NIST hash algorithms can be found on their "Policy on Hash Functions" page.

    • SHA-1 produces a bit hash value and was originally published as FIPS PUB and RFC SHA-1 was deprecated by NIST as of the end of although it is still widely used.

    • SHA-2, originally described in FIPS PUB and eventually replaced by FIPS PUB (and FIPS PUB ), comprises five algorithms in the SHS: SHA-1 plus SHA, SHA, SHA, and SHA which can produce hash values that are , , , or bits in length, respectively. SHA-2 recommends use of SHA-1, SHA, and SHA for messages less than 264 bits in length, and employs a bit block size; SHA and SHA are recommended for messages less than 2 bits in length, and employs a 1, bit block size. FIPS PUB also introduces the concept of a truncated hash in SHA/t, a generic name referring to a hash value based upon the SHA algorithm that has been truncated to t bits; SHA/ and SHA/ are specifically described. SHA, , , and are also described in RFC

    • SHA-3 is the current SHS algorithm. Although there had not been any successful attacks on SHA-2, NIST decided that having an alternative to SHA-2 using a different algorithm would be prudent. In , they launched a SHA-3 Competition to find that alternative; a list of submissions can be found at The SHA-3 Zoo. In , NIST announced that after reviewing 64 submissions, the winner was Keccak (pronounced "catch-ack"), a family of hash algorithms based on sponge functions. The NIST version can support hash output sizes of and bits.

  • RIPEMD: A series of message digests that initially came from the RIPE (RACE Integrity Primitives Evaluation) project. RIPEMD was designed by Hans Dobbertin, Antoon Bosselaers, and Bart Preneel, and optimized for bit processors to replace the then-current bit hash functions. Other versions include RIPEMD, RIPEMD, and RIPEMD

  • eD2k: Named for the EDonkey Network (eD2K), the eD2k hash is a root hash of an MD4 hash list of a given file. A root hash is used on peer-to-peer file transfer networks, where a file is broken into chunks; each chunk has its own MD4 hash associated with it and the server maintains a file that contains the hash list of all of the chunks. The root hash is the hash of the hash list file.

  • HAVAL (HAsh of VAriable Length): Designed by Y. Zheng, J. Pieprzyk and J. Seberry, a hash algorithm with many levels of security. HAVAL can create hash values that are , , , , or bits in length. More details can be found in "HAVAL - A one-way hashing algorithm with variable length output" by Zheng, Pieprzyk, and Seberry (AUSCRYPT '92).

  • The Skein Hash Function Family: The Skein Hash Function Family was proposed to NIST in their hash function competition. Skein is fast due to using just a few simple computational primitives, secure, and very flexible &#; per the specification, it can be used as a straight-forward hash, MAC, HMAC, digital signature hash, key derivation mechanism, stream cipher, or pseuo-random number generator. Skein supports internal state sizes of , and bits, and arbitrary output lengths.

  • SM3: SM3 is a bit hash function operating on bit input blocks. Part of a Chinese National Standard, SM3 is issued by the Chinese State Cryptographic Authority as GM/T SM3 cryptographic hash algorithm () and GB/T Information security techniques—SM3 cryptographic hash algorithm (). More information can also be found at the SM3 (hash function) page.

  • Tiger: Designed by Ross Anderson and Eli Biham, Tiger is designed to be secure, run efficiently on bit processors, and easily replace MD4, MD5, SHA and SHA-1 in other applications. Tiger/ produces a bit output and is compatible with bit architectures; Tiger/ and Tiger/ produce a hash of length and bits, respectively, to provide compatibility with the other hash functions mentioned above.

  • Whirlpool: Designed by V. Rijmen (co-inventor of Rijndael) and P.S.L.M. Barreto, Whirlpool is one of two hash functions endorsed by the NESSIE competition (the other being SHA). Whirlpool operates on messages less than 2 bits in length and produces a message digest of bits. The design of this hash function is very different than that of MD5 and SHA-1, making it immune to the types of attacks that succeeded on those hashes.

Readers might be interested in HashCalc, a Windows-based program that calculates hash values using a dozen algorithms, including MD5, SHA-1 and several variants, RIPEMD, and Tiger. Command line utilities that calculate hash values include sha_verify by Dan Mares (Windows; supports MD5, SHA-1, SHA-2) and md5deep (cross-platform; supports MD5, SHA-1, SHA, Tiger, and Whirlpool).


A digression on hash collisions. Hash functions are sometimes misunderstood and some sources claim that no two files can have the same hash value. This is in theory, if not in fact, incorrect. Consider a hash function that provides a bit hash value. There are, then, 2 possible hash values. But there are an infinite number of possible files and &#; >> 2. Therefore, there have to be multiple files &#; in fact, there have to be an infinite number of files! &#; that have the same bit hash value. (Now, while even this is theoretically correct, it is not true in practice because hash algorithms are designed to work with a limited message size, as mentioned above. For example, SHA-1, SHA, and SHA produce hash values that are , , and bits in length, respectively, and limit the message length to less than 264 bits; SHA and all SHA variants limit the message length to less than 2 bits. Nevertheless, hopefully you get my point &#; and, alas, even if you don't, do know that there are multiple files that have the same MD5 or SHA-1 hash values.)

The difficulty is not necessarily in finding two files with the same hash, but in finding a second file that has the same hash value as a given first file. Consider this example. A human head has, generally, no more than ~, hairs. Since there are more than 7 billion people on earth, we know that there are a lot of people with the same number of hairs on their head. Finding two people with the same number of hairs, then, would be relatively simple. The harder problem is choosing one person (say, you, the reader) and then finding another person who has the same number of hairs on their head as you have on yours.

This is somewhat similar to the Birthday Problem. We know from probability that if you choose a random group of ~23 people, the probability is about 50% that two will share a birthday (the probability goes up to % with a group of 70 people). However, if you randomly select one person in a group of 23 and try to find a match to that person, the probability is only about 6% of finding a match; you'd need a group of for a 50% probability of a shared birthday to one of the people chosen at random (and a group of more than 4, to obtain a % probability).

What is hard to do, then, is to try to create a file that matches a given hash value so as to force a hash value collision &#; which is the reason that hash functions are used extensively for information security and computer forensics applications. Alas, researchers as far back as found that practical collision attacks could be launched on MD5, SHA-1, and other hash algorithms and, today, it is generally recognized that MD5 and SHA-1 are pretty much broken. Readers interested in this problem should read the following:

  • AccessData. (, April). MD5 Collisions: The Effect on Computer Forensics. AccessData White Paper.
  • Burr, W. (, March/April). Cryptographic hash standards: Where do we go from here?IEEE Security & Privacy, 4(2),
  • Dwyer, D. (, June 3). SHA-1 Collision Attacks Now 252. SecureWorks Research blog.
  • Gutman, P., Naccache, D., & Palmer, C.C. (, May/June). When hashes collide. IEEE Security & Privacy, 3(3),
  • Kessler, G.C. (). The Impact of MD5 File Hash Collisions on Digital Forensic Imaging. Journal of Digital Forensics, Security & Law, 11(4),
  • Kessler, G.C. (). The Impact of SHA-1 File Hash Collisions on Digital Forensic Imaging: A Follow-Up Experiment. Journal of Digital Forensics, Security & Law, 11(4),
  • Klima, V. (, March). Finding MD5 Collisions - a Toy For a Notebook.
  • Lee, R. (, January 7). Law Is Not A Science: Admissibility of Computer Evidence and MD5 Hashes. SANS Computer Forensics blog.
  • Leurent, G. & Peyrin, T. (, January). SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust. Real World Crypto .
  • Leurent, G. & Peyrin, T. (, January). SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust.(paper)
  • Stevens, M., Bursztein, E., Karpman, P., Albertini, A., & Markov, Y. (). The first collision for full SHA
  • Stevens, M., Karpman, P., & Peyrin, T. (, October 8). Freestart collision on full SHA Cryptology ePrint Archive, Report /
  • Thompson, E. (, February). MD5 collisions and the impact on computer forensics. Digital Investigation, 2(1),
  • Wang, X., Feng, D., Lai, X., & Yu, H. (, August). Collisions for Hash Functions MD4, MD5, HAVAL and RIPEMD.
  • Wang, X., Yin, Y.L., & Yu, H. (, February 13). Collision Search Attacks on SHA1.

Readers are also referred to the Eindhoven University of Technology HashClash Project Web site. for For additional information on hash functions, see David Hopwood's MessageDigest Algorithms page and Peter Selinger's MD5 Collision Demo page. For historical purposes, take a look at the situation with hash collisions, circa , in RFC

In October , the SHA-1 Freestart Collision was announced; see a report by Bruce Schneier and the developers of the attack (as well as the paper above by Stevens et al. ()). In February , the first SHA-1 collision was announced on the Google Security Blog and Centrum Wiskunde & Informatica's Shattered page. See also the paper by Stevens et al. (), listed above. If ths isn't enough, see the SHA-1 is a Shambles Web page and the Leurent & Peyrin paper, listed above.

For an interesting twist on this discussion, read about the Nostradamus attack reported at Predicting the winner of the US Presidential Elections using a Sony PlayStation 3 (by M. Stevens, A.K. Lenstra, and B. de Weger, November ).


Finally, note that certain extensions of hash functions are used for a variety of information security and digital forensics applications, such as:

  • Hash libraries, aka hashsets, are sets of hash values corresponding to known files. A hashset containing the hash values of all files known to be a part of a given operating system, for example, could form a set of known good files, and could be ignored in an investigation for malware or other suspicious file, whereas as hash library of known child pornographic images could form a set of known bad files and be the target of such an investigation.
  • Rolling hashes refer to a set of hash values that are computed based upon a fixed-length "sliding window" through the input. As an example, a hash value might be computed on bytes of a file, then on bytes , , , etc.
  • Fuzzy hashes are an area of intense research and represent hash values that represent two inputs that are similar. Fuzzy hashes are used to detect documents, images, or other files that are close to each other with respect to content. See "Fuzzy Hashing" by Jesse Kornblum for a good treatment of this topic.

Why Three Encryption Techniques?

So, why are there so many different types of cryptographic schemes? Why can't we do everything we need with just one?

The answer is that each scheme is optimized for some specific cryptographic application(s). Hash functions, for example, are well-suited for ensuring data integrity because any change made to the contents of a message will result in the receiver calculating a different hash value than the one placed in the transmission by the sender. Since it is highly unlikely that two different messages will yield the same hash value, data integrity is ensured to a high degree of confidence.

Secret key cryptography, on the other hand, is ideally suited to encrypting messages, thus providing privacy and confidentiality. The sender can generate a session key on a per-message basis to encrypt the message; the receiver, of course, needs the same session key in order to decrypt the message.

Key exchange, of course, is a key application of public key cryptography (no pun intended). Asymmetric schemes can also be used for non-repudiation and user authentication; if the receiver can obtain the session key encrypted with the sender's private key, then only this sender could have sent the message. Public key cryptography could, theoretically, also be used to encrypt messages although this is rarely done because secret key cryptography values can generally be computed about times faster than public key cryptography values.

FIGURE 4: Use of the three cryptographic techniques for secure communication.


Figure 4 puts all of this together and shows how a hybrid cryptographic scheme combines all of these functions to form a secure transmission comprising a digital signature and digital envelope. In this example, the sender of the message is Alice and the receiver is Bob.

A digital envelope comprises an encrypted message and an encrypted session key. Alice uses secret key cryptography to encrypt her message using the session key, which she generates at random with each session. Alice then encrypts the session key using Bob's public key. The encrypted message and encrypted session key together form the digital envelope. Upon receipt, Bob recovers the session secret key using his private key and then decrypts the encrypted message.

The digital signature is formed in two steps. First, Alice computes the hash value of her message; next, she encrypts the hash value with her private key. Upon receipt of the digital signature, Bob recovers the hash value calculated by Alice by decrypting the digital signature with Alice's public key. Bob can then apply the hash function to Alice's original message, which he has already decrypted (see previous paragraph). If the resultant hash value is not the same as the value supplied by Alice, then Bob knows that the message has been altered; if the hash values are the same, Bob should believe that the message he received is identical to the one that Alice sent.

This scheme also provides nonrepudiation since it proves that Alice sent the message; if the hash value recovered by Bob using Alice's public key proves that the message has not been altered, then only Alice could have created the digital signature. Bob also has proof that he is the intended receiver; if he can correctly decrypt the message, then he must have correctly decrypted the session key meaning that his is the correct private key.

This diagram purposely suggests a cryptosystem where the session key is used for just a single session. Even if this session key is somehow broken, only this session will be compromised; the session key for the next session is not based upon the key for this session, just as this session's key was not dependent on the key from the previous session. This is known as Perfect Forward Secrecy; you might lose one session key due to a compromise but you won't lose all of them. (This was an issue in the OpenSSL vulnerability known as Heartbleed.)

The Significance of Key Length

In a article in the industry literature, a writer made the claim that bit keys did not provide as adequate protection for DES at that time as they did in because computers were times faster in than in Therefore, the writer went on, we needed 56,bit keys in instead of bit keys to provide adequate protection. The conclusion was then drawn that because 56,bit keys are infeasible (true), we should accept the fact that we have to live with weak cryptography (false!). The major error here is that the writer did not take into account that the number of possible key values double whenever a single bit is added to the key length; thus, a bit key has twice as many values as a bit key (because 257 is two times 256). In fact, a bit key would have times more values than a bit key.

But this does bring up the question &#; "What is the significance of key length as it affects the level of protection?"

In cryptography, size does matter. The larger the key, the harder it is to crack a block of encrypted data. The reason that large keys offer more protection is almost obvious; computers have made it easier to attack ciphertext by using brute force methods rather than by attacking the mathematics (which are generally well-known anyway). With a brute force attack, the attacker merely generates every possible key and applies it to the ciphertext. Any resulting plaintext that makes sense offers a candidate for a legitimate key. This was the basis, of course, of the EFF's attack on DES.

Until the mids or so, brute force attacks were beyond the capabilities of computers that were within the budget of the attacker community. By that time, however, significant compute power was typically available and accessible. General-purpose computers such as PCs were already being used for brute force attacks. For serious attackers with money to spend, such as some large companies or governments, Field Programmable Gate Array (FPGA) or Application-Specific Integrated Circuits (ASIC) technology offered the ability to build specialized chips that could provide even faster and cheaper solutions than a PC. As an example, the AT&T Optimized Reconfigurable Cell Array (ORCA) FPGA chip cost about $ and could test 30 million DES keys per second, while a $10 ASIC chip could test million DES keys per second; compare that to a PC which might be able to test 40, keys per second. Distributed attacks, harnessing the power of up to tens of thousands of powerful CPUs, are now commonly employed to try to brute-force crypto keys.

Type of AttackerBudgetToolTime and Cost
Per Key Recovered
Key Length Needed
For Protection
In Late
40 bits56 bits
Pedestrian HackerTinyScavenged
computer
time
1 weekInfeasible45
$FPGA5 hours
($)
38 years
($5,)
50
Small Business$10,FPGA12 minutes
($)
18 months
($5,)
55
Corporate Department$KFPGA24 seconds
($)
19 days
($5,)
60
ASIC seconds
($)
3 hours
($38)
Big Company$10MFPGA7 seconds
($)
13 hours
($5,)
70
ASIC seconds
($)
6 minutes
($38)
Intelligence Agency$MASIC seconds
($)
12 seconds
($38)
75

Table 2 &#; from a article discussing both why exporting bit keys was, in essence, no crypto at all and why DES' days were numbered &#; shows what DES key sizes were needed to protect data from attackers with different time and financial resources. This information was not merely academic; one of the basic tenets of any security system is to have an idea of what you are protecting and from whom are you protecting it! The table clearly shows that a bit key was essentially worthless against even the most unsophisticated attacker. On the other hand, bit keys were fairly strong unless you might be subject to some pretty serious corporate or government espionage. But note that even bit keys were clearly on the decline in their value and that the times in the table were worst cases.

So, how big is big enough? DES, invented in , was still in use at the turn of the century, nearly 25 years later. If we take that to be a design criteria (i.e., a plus year lifetime) and we believe Moore's Law ("computing power doubles every 18 months"), then a key size extension of 14 bits (i.e., a factor of more than 16,) should be adequate. The DES proposal suggested bit keys; by , a bit key would have been required to offer equal protection and an bit key necessary by

A or bit SKC key will probably suffice for some time because that length keeps us ahead of the brute force capabilities of the attackers. Note that while a large key is good, a huge key may not always be better; for example, expanding PKC keys beyond the current or bit lengths doesn't add any necessary protection at this time. Weaknesses in cryptosystems are largely based upon key management rather than weak keys.

Much of the discussion above, including the table, is based on the paper "Minimal Key Lengths for Symmetric Ciphers to Provide Adequate Commercial Security" by M. Blaze, W. Diffie, R.L. Rivest, B. Schneier, T. Shimomura, E. Thompson, and M. Wiener ().

The most effective large-number factoring methods today use a mathematical Number Field Sieve to find a certain number of relationships and then uses a matrix operation to solve a linear equation to produce the two prime factors. The sieve step actually involves a large number of operations that can be performed in parallel; solving the linear equation, however, requires a supercomputer. Indeed, finding the solution to the RSA challenge in February &#; factoring a digit (bit) prime number &#; required computers across the Internet about 4 weeks for the first step and a Cray computer hours and MB of memory to do the second step.

In early , Shamir (of RSA fame) described a new machine that could increase factorization speed by orders of magnitude. Although no detailed plans were provided nor is one known to have been built, the concepts of TWINKLE (The Weizmann Institute Key Locating Engine) could result in a specialized piece of hardware that would cost about $ and have the processing power of PCs. There still appear to be many engineering details that have to be worked out before such a machine could be built. Furthermore, the hardware improves the sieve step only; the matrix operation is not optimized at all by this design and the complexity of this step grows rapidly with key length, both in terms of processing time and memory requirements. Nevertheless, this plan conceptually puts bit keys within reach of being factored. Although most PKC schemes allow keys that are bits and longer, Shamir claims that bit RSA keys "protect 95% of today's E-commerce on the Internet." (See Bruce Schneier's Crypto-Gram (May 15, ) for more information.)

It is also interesting to note that while cryptography is good and strong cryptography is better, long keys may disrupt the nature of the randomness of data files. Shamir and van Someren ("Playing hide and seek with stored keys") have noted that a new generation of viruses can be written that will find files encrypted with long keys, making them easier to find by intruders and, therefore, more prone to attack.

Finally, U.S. government policy has tightly controlled the export of crypto products since World War II. Until the mids, export outside of North America of cryptographic products using keys greater than 40 bits in length was prohibited, which made those products essentially worthless in the marketplace, particularly for electronic commerce; today, crypto products are widely available on the Internet without restriction. The U.S. Department of Commerce Bureau of Industry and Security maintains an Encryption FAQ web page with more information about the current state of encryption registration.


Without meaning to editorialize too much in this tutorial, a bit of historical context might be helpful. In the mids, the U.S. Department of Commerce still classified cryptography as a munition and limited the export of any products that contained crypto. For that reason, browsers in the era, such as Internet Explorer and Netscape, had a domestic version with bit encryption (downloadable only in the U.S.) and an export version with bit encryption. Many cryptographers felt that the export limitations should be lifted because they only applied to U.S. products and seemed to have been put into place by policy makers who believed that only the U.S. knew how to build strong crypto algorithms, ignoring the work ongoing in Australia, Canada, Israel, South Africa, the U.K., and other locations in the s. Those restrictions were lifted by or , but there is still a prevailing attitude, apparently, that U.S. crypto algorithms are the only strong ones around; consider Bruce Schneier's blog in June titled "CIA Director John Brennan Pretends Foreign Cryptography Doesn't Exist." Cryptography is a decidedly international game today; note the many countries mentioned above as having developed various algorithms, not the least of which is the fact that NIST's Advanced Encryption Standard employs an algorithm submitted by cryptographers from Belgium. For more evidence, see Schneier's Worldwide Encryption Products Survey (February ).


On a related topic, public key crypto schemes can be used for several purposes, including key exchange, digital signatures, authentication, and more. In those PKC systems used for SKC key exchange, the PKC key lengths are chosen so as to be resistant to some selected level of attack. The length of the secret keys exchanged via that system have to have at least the same level of attack resistance. Thus, the three parameters of such a system &#; system strength, secret key strength, and public key strength &#; must be matched. This topic is explored in more detail in Determining Strengths For Public Keys Used For Exchanging Symmetric Keys (RFC ).

4. TRUST MODELS

Secure use of cryptography requires trust. While secret key cryptography can ensure message confidentiality and hash codes can ensure integrity, none of this works without trust. In SKC, Alice and Bob had to share a secret key. PKC solved the secret distribution problem, but how does Alice really know that Bob is who he says he is? Just because Bob has a public and private key, and purports to be "Bob," how does Alice know that a malicious person (Mallory) is not pretending to be Bob?

There are a number of trust models employed by various cryptographic schemes. This section will explore three of them:

  • The web of trust employed by Pretty Good Privacy (PGP) users, who hold their own set of trusted public keys.
  • Kerberos, a secret key distribution scheme using a trusted third party.
  • Certificates, which allow a set of trusted third parties to authenticate each other and, by implication, each other's users.

Each of these trust models differs in complexity, general applicability, scope, and scalability.

PGP Web of Trust

Pretty Good Privacy (described more below in Section ) is a widely used private e-mail scheme based on public key methods. A PGP user maintains a local keyring of all their known and trusted public keys. The user makes their own determination about the trustworthiness of a key using what is called a "web of trust."

FIGURE 5: GPG keychain.

Figure 5 shows a PGP-formatted keychain from the GNU Privacy Guard (GPG) software, an implementation of the OpenPGP standard. This is a section of my keychain, so only includes public keys from individuals whom I know and, presumably, trust. Note that keys are associated with e-mail addresses rather than individual names.

In general, the PGP Web of trust works as follows. Suppose that Alice needs Bob's public key. Alice could just ask Bob for it directly via e-mail or download the public key from a PGP key server; this server might a well-known PGP key repository or a site that Bob maintains himself. In fact, Bob's public key might be stored or listed in many places. (My public key, for example, can be found at storycall.us or at several public PGP key servers, including storycall.us.) Alice is prepared to believe that Bob's public key, as stored at these locations, is valid.

Suppose Carol claims to hold Bob's public key and offers to give the key to Alice. How does Alice know that Carol's version of Bob's key is valid or if Carol is actually giving Alice a key that will allow Mallory access to messages? The answer is, "It depends." If Alice trusts Carol and Carol says that she thinks that her version of Bob's key is valid, then Alice may &#; at her option &#; trust that key. And trust is not necessarily transitive; if Dave has a copy of Bob's key and Carol trusts Dave, it does not necessarily follow that Alice trusts Dave even if she does trust Carol.

The point here is that who Alice trusts and how she makes that determination is strictly up to Alice. PGP makes no statement and has no protocol about how one user determines whether they trust another user or not. In any case, encryption and signatures based on public keys can only be used when the appropriate public key is on the user's keyring.

Kerberos

Kerberos is a commonly used authentication scheme on the Internet. Developed by MIT's Project Athena, Kerberos is named for the three-headed dog who, according to Greek mythology, guards the entrance of Hades (rather than the exit, for some reason!).

Kerberos employs a client/server architecture and provides user-to-server authentication rather than host-to-host authentication. In this model, security and authentication will be based on secret key technology where every host on the network has its own secret key. It would clearly be unmanageable if every host had to know the keys of all other hosts so a secure, trusted host somewhere on the network, known as a Key Distribution Center (KDC), knows the keys for all of the hosts (or at least some of the hosts within a portion of the network, called a realm). In this way, when a new node is brought online, only the KDC and the new node need to be configured with the node's key; keys can be distributed physically or by some other secure means.

FIGURE 6: Kerberos architecture.


The Kerberos Server/KDC has two main functions (Figure 6), known as the Authentication Server (AS) and Ticket-Granting Server (TGS). The steps in establishing an authenticated session between an application client and the application server are:
  1. The Kerberos client software establishes a connection with the Kerberos server's AS function. The AS first authenticates that the client is who it purports to be. The AS then provides the client with a secret key for this login session (the TGS session key) and a ticket-granting ticket (TGT), which gives the client permission to talk to the TGS. The ticket has a finite lifetime so that the authentication process is repeated periodically.
  2. The client now communicates with the TGS to obtain the Application Server's key so that it (the client) can establish a connection to the service it wants. The client supplies the TGS with the TGS session key and TGT; the TGS responds with an application session key (ASK) and an encrypted form of the Application Server's secret key; this secret key is never sent on the network in any other form.
  3. The client has now authenticated itself and can prove its identity to the Application Server by supplying the Kerberos ticket, application session key, and encrypted Application Server secret key. The Application Server responds with similarly encrypted information to authenticate itself to the client. At this point, the client can initiate the intended service requests (e.g., Telnet, FTP, HTTP, or e-commerce transaction session establishment).

The current version of this protocol is Kerberos V5 (described in RFC ). While the details of their operation, functional capabilities, and message formats are different, the conceptual overview above pretty much holds for both. One primary difference is that Kerberos V4 uses only DES to generate keys and encrypt messages, while V5 allows other schemes to be employed (although DES is still the most widely algorithm used).

Public Key Certificates and Certificate Authorities

Certificates and Certificate Authorities (CA) are necessary for widespread use of cryptography for e-commerce applications. While a combination of secret and public key cryptography can solve the business issues discussed above, crypto cannot alone address the trust issues that must exist between a customer and vendor in the very fluid, very dynamic e-commerce relationship. How, for example, does one site obtain another party's public key? How does a recipient determine if a public key really belongs to the sender? How does the recipient know that the sender is using their public key for a legitimate purpose for which they are authorized? When does a public key expire? How can a key be revoked in case of compromise or loss?

The basic concept of a certificate is one that is familiar to all of us. A driver's license, credit card, or SCUBA certification, for example, identify us to others, indicate something that we are authorized to do, have an expiration date, and identify the authority that granted the certificate.

As complicated as this may sound, it really isn't. Consider driver's licenses. I have one issued by the State of Florida. The license establishes my identity, indicates the type of vehicles that I can operate and the fact that I must wear corrective lenses while doing so, identifies the issuing authority, and notes that I am an organ donor. When I drive in other states, the other jurisdictions throughout the U.S. recognize the authority of Florida to issue this "certificate" and they trust the information it contains. When I leave the U.S., everything changes. When I am in Aruba, Australia, Canada, Israel, and many other countries, they will accept not the Florida license, per se, but any license issued in the U.S. This analogy represents the certificate trust chain, where even certificates carry certificates.

For purposes of electronic transactions, certificates are digital documents. The specific functions of the certificate include:

  • Establish identity: Associate, or bind, a public key to an individual, organization, corporate position, or other entity.
  • Assign authority: Establish what actions the holder may or may not take based upon this certificate.
  • Secure confidential information (e.g., encrypting the session's symmetric key for data confidentiality).

Typically, a certificate contains a public key, a name, an expiration date, the name of the authority that issued the certificate (and, therefore, is vouching for the identity of the user), a serial number, any pertinent policies describing how the certificate was issued and/or how the certificate may be used, the digital signature of the certificate issuer, and perhaps other information.

FIGURE 7: VeriSign Class 3 certificate.

A sample abbreviated certificate is shown in Figure 7. This is a typical certificate found in a browser, in this case, Mozilla Firefox (MacOS). While this is a certificate issued by VeriSign, many root-level certificates can be found shipped with browsers. When the browser makes a connection to a secure Web site, the Web server sends its public key certificate to the browser. The browser then checks the certificate's signature against the public key that it has stored; if there is a match, the certificate is taken as valid and the Web site verified by this certificate is considered to be "trusted."

The most widely accepted certificate format is the one defined in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Recommendation X Rec. X is a specification used around the world and any applications complying with X can share certificates. Most certificates today comply with X Version 3 and contain the following information:

  • Version number
  • Certificate serial number
  • Signature algorithm identifier
  • Issuer's name and unique identifier
  • Validity (or operational) period
  • Subject's name and unique identifier
  • Subject public key information
  • Standard extensions
    • Certificate appropriate use definition
    • Key usage limitation definition
    • Certificate policy information
  • Other extensions
    • Application-specific
    • CA-specific

Certificate authorities are the repositories for public keys and can be any agency that issues certificates. A company, for example, may issue certificates to its employees, a college/university to its students, a store to its customers, an Internet service provider to its users, or a government to its constituents.

When a sender needs an intended receiver's public key, the sender must get that key from the receiver's CA. That scheme is straight-forward if the sender and receiver have certificates issued by the same CA. If not, how does the sender know to trust the foreign CA? One industry wag has noted, about trust: "You are either born with it or have it granted upon you." Thus, some CAs will be trusted because they are known to be reputable, such as the CAs operated by AT&T Services, Comodo, DigiCert (formerly GTE Cybertrust), EnTrust, Broadcom (formerly Symantec, formerly VeriSign), and Thawte. CAs, in turn, form trust relationships with other CAs. Thus, if a user queries a foreign CA for information, the user may ask to see a list of CAs that establish a "chain of trust" back to the user.

One major feature to look for in a CA is their identification policies and procedures. When a user generates a key pair and forwards the public key to a CA, the CA has to check the sender's identification and takes any steps necessary to assure itself that the request is really coming from the advertised sender. Different CAs have different identification policies and will, therefore, be trusted differently by other CAs. Verification of identity is just one of many issues that are part of a CA's Certification Practice Statement (CPS) and policies; other issues include how the CA protects the public keys in its care, how lost or compromised keys are revoked, and how the CA protects its own private keys.

As a final note, CAs are not immune to attack and certificates themselves are able to be counterfeited. One of the first such episodes occurred at the turn of the century; on January 29 and 30, , two VeriSign Class 3 code-signing digital certificates were issued to an individual who fraudulently claimed to be a Microsoft employee (CERT/CC CA and Microsoft Security Bulletin MS - Critical). Problems have continued over the years; good write-ups on this can be found at "Another Certification Authority Breached (the 12th!)" and "How Cybercrime Exploits Digital Certificates." Readers are also urged to read "Certification Authorities Under Attack: A Plea for Certificate Legitimation" (Oppliger, R., January/February , IEEE Internet Computing, 18(1), ).

As a partial way to address this issue, the Internet Security Research Group (ISRG) designed the Automated Certificate Management Environment (ACME) protocol. ACME is a communications protocol that streamlines the process of deploying a Public Key Infrastructure (PKI) by automating interactions between CAs and Web servers that wish to obtain a certificate. More information can be found at the Let's Encrypt Web site, an ACME-based CA service provided by the ISRG.

Summary

The paragraphs above describe three very different trust models. It is hard to say that any one is better than the others; it depends upon your application. One of the biggest and fastest growing applications of cryptography today, though, is electronic commerce (e-commerce), a term that itself begs for a formal definition.

PGP's web of trust is easy to maintain and very much based on the reality of users as people. The model, however, is limited; just how many public keys can a single user reliably store and maintain? And what if you are using the "wrong" computer when you want to send a message and can't access your keyring? How easy it is to revoke a key if it is compromised? PGP may also not scale well to an e-commerce scenario of secure communication between total strangers on short-notice.

Kerberos overcomes many of the problems of PGP's web of trust, in that it is scalable and its scope can be very large. However, it also requires that the Kerberos server have a priori knowledge of all client systems prior to any transactions, which makes it unfeasible for "hit-and-run" client/server relationships as seen in e-commerce.

Certificates and the collection of CAs will form a PKI. In the early days of the Internet, every host had to maintain a list of every other host; the Domain Name System (DNS) introduced the idea of a distributed database for this purpose and the DNS is one of the key reasons that the Internet has grown as it has. A PKI will fill a similar void in the e-commerce and PKC realm.

While certificates and the benefits of a PKI are most often associated with electronic commerce, the applications for PKI are much broader and include secure electronic mail, payments and electronic checks, Electronic Data Interchange (EDI), secure transfer of Domain Name System (DNS) and routing information, electronic forms, and digitally signed documents. A single "global PKI" is still many years away, that is the ultimate goal of today's work as international electronic commerce changes the way in which we do business in a similar way in which the Internet has changed the way in which we communicate.

5. CRYPTOGRAPHIC ALGORITHMS IN ACTION

The paragraphs above have provided an overview of the different types of cryptographic algorithms, as well as some examples of some available protocols and schemes. Table 3 provides a list of some other noteworthy schemes and cryptosystems employed &#; or proposed &#; for a variety of functions, most notably electronic commerce and secure communication. The paragraphs below will show several real cryptographic applications that many of us employ (knowingly or not) everyday for password protection and private communication. Some of the schemes described below never were widely deployed but are still historically interesting, thus remain included here. This list is, by no means, exhaustive but describes items that are of significant current and/or historic importance (a subjective judgement, to be sure).

BitmessageA decentralized, encrypted, peer-to-peer, trustless communications protocol for message exchange. The decentralized design, outlined in "Bitmessage: A Peer-to-Peer Message Authentication and Delivery System" (Warren, ), is conceptually based on the Bitcoin model.
CapstoneA now-defunct U.S. National Institute of Standards and Technology (NIST) and National Security Agency (NSA) project under the Bush Sr. and Clinton administrations for publicly available strong cryptography with keys escrowed by the government (NIST and the Treasury Dept.). Capstone included one or more tamper-proof computer chips for implementation (Clipper), a secret key encryption algorithm (Skipjack), digital signature algorithm (DSA), key exchange algorithm (KEA), and hash algorithm (SHA).
Challenge-Handshake Authentication Protocol (CHAP)An authentication scheme that allows one party to prove who they are to a second party by demonstrating knowledge of a shared secret without actually divulging that shared secret to a third party who might be listening. Described in RFC
Chips-Message Robust Authentication (CHIMERA)A scheme proposed for authenticating navigation data and the spreading code of civilian signals in the Global Positioning System (GPS). This is an anti-spoofing mechanism to protect the unencrypted civilian signals; GPS military signals are encrypted.
ClipperThe computer chip that would implement the Skipjack encryption scheme. The Clipper chip was to have had a deliberate backdoor so that material encrypted with this device would not be beyond the government's reach. Described in , Clipper was dead by See also EPIC's The Clipper Chip Web page.
Cryptography Research and Evaluation Committees (CRYPTEC)Similar in concept to the NIST AES process and NESSIE, CRYPTEC is the Japanese government's process to evaluate algorithms submitted for government and industry applications. CRYPTEX maintains a list of public key and secret key ciphers, hash functions, MACs, and other crypto algorithms approved for various applications in government environments.
Derived Unique Key Per Transaction (DUKPT)A key management scheme used for debit and credit card verification with point-of-sale (POS) transaction systems, automated teller machines (ATMs), and other financial applications. In DUKPT, a unique key is derived for each transaction based upon a fixed, shared key in such a way that knowledge of one derived key does not easily yield knowledge of other keys (including the fixed key). Therefore, if one of the derived keys is compromised, neither past nor subsequent transactions are endangered. DUKPT is specified in American National Standard (ANS) ANSI X (Retail Financial Services Symmetric Key Management Part 1: Using Symmetric Techniques) and can be purchased at the ANSI X Web page.
ECRYPT Stream Cipher Project (eSTREAM)The eSTREAM project came about as a result of the failure of the NESSIE project to produce a stream cipher that survived cryptanalysis. eSTREAM ran from to with the primary purpose of promoting the design of efficient and compact stream ciphers. As of September , the eSTREAM suite contains seven sciphers.
Escrowed Encryption Standard (EES)Largely unused, a controversial crypto scheme employing the SKIPJACK secret key crypto algorithm and a Law Enforcement Access Field (LEAF) creation method. LEAF was one part of the key escrow system and allowed for decryption of ciphertext messages that had been intercepted by law enforcement agencies. Described more in FIPS PUB (archived; no longer in force).
Federal Information Processing Standards (FIPS)These computer security- and crypto-related FIPS PUBs are produced by the U.S. National Institute of Standards and Technology (NIST) as standards for the U.S. Government. Current Federal Information Processing Standards (FIPS) related to crytography include:
FortezzaA PCMCIA card developed by NSA that implements the Capstone algorithms, intended for use with the Defense Messaging Service (DMS). Originally called Tessera.
GOSTGOST is a family of algorithms defined in the Russian cryptographic standards. Although most of the specifications are written in Russian, a series of RFCs describe some of the aspects so that the algorithms can be used effectively in Internet applications:
  • RFC Additional Cryptographic Algorithms for Use with GOST , GOST R , GOST R , and GOST R Algorithms
  • RFC Using the GOST , GOST R , GOST R , and GOST R Algorithms with Cryptographic Message Syntax (CMS)
  • RFC Using the GOST R , GOST R , and GOST R Algorithms with the Internet X Public Key Infrastructure Certificate and CRL Profile
  • RFC GOST Encryption, Decryption, and Message Authentication Code (MAC) Algorithms
  • RFC GOST R Hash Function Algorithm
  • RFC GOST R Digital Signature Algorithm (Updates RFC GOST R )
  • RFC GOST R Block Cipher "Kuznyechik"
  • RFC Guidelines on the Cryptographic Algorithms to Accompany the Usage of Standards GOST R and GOST R
  • RFC GOST R Block Cipher "Magma"
IP Security (IPsec)The IPsec protocol suite is used to provide privacy and authentication services at the IP layer. An overview of the protocol suite and of the documents comprising IPsec can be found in RFC Other documents include:
  • RFC IP security architecture.
  • RFC IP Authentication Header (AH), one of the two primary IPsec functions; AH provides connectionless integrity and data origin authentication for IP datagrams and protects against replay attacks.
  • RFC IP Encapsulating Security Payload (ESP), the other primary IPsec function; ESP provides a variety of security services within IPsec.
  • RFC Extended Sequence Number (ESN) Addendum, allows for negotiation of a or bit sequence number, used to detect replay attacks.
  • RFC Cryptographic algorithm implementation requirements for ESP and AH.
  • RFC The Internet Key Exchange (IKE) protocol, version 2, providing for mutual authentication and establishing and maintaining security associations.
    • IKE v1 was described in three separate documents, RFC (application of ISAKMP to IPsec), RFC (ISAKMP, a framework for key management and security associations), and RFC (IKE, using part of Oakley and part of SKEME in conjunction with ISAKMP to obtain authenticated keying material for use with ISAKMP, and for other security associations such as AH and ESP). IKE v1 is obsoleted with the introduction of IKEv2.
  • RFC Cryptographic algorithms used with IKEv2.
  • RFC Crypto suites for IPsec, IKE, and IKEv2.
  • RFC The use of AES in CBC-MAC mode with IPsec ESP.
  • RFC The use of the Camellia cipher algorithm in IPsec.
  • RFC The Use of RSA/SHA-1 Signatures within Encapsulating Security Payload (ESP) and Authentication Header (AH).
  • RFC Describes AES-XCBC-PRF, a pseudo-random function derived from the AES for use with IKE.
  • RFC Describes use of the HMAC with MD5 algorithm for data origin authentication and integrity protection in both AH and ESP.
  • RFC Describes use of DES-CBC (DES in Cipher Block Chaining Mode) for confidentiality in ESP.
  • RFC Defines use of the NULL encryption algorithm (i.e., provides authentication and integrity without confidentiality) in ESP.
  • RFC Describes OAKLEY, a key determination and distribution protocol.
  • RFC Describes use of Cipher Block Chaining (CBC) mode cipher algorithms with ESP.
  • RFCs and Description of Photuris, a session-key management protocol for IPsec.

In addition, RFC describes Suite B Cryptographic Suites for IPsec and RFC describes the Suite B profile for IPsec.

IPsec was first proposed for use with IP version 6 (IPv6), but can also be employed with the current IP version, IPv4.

(See more detail about IPsec below in Section )

Internet Security Association and Key Management Protocol (ISAKMP/OAKLEY)ISAKMP/OAKLEY provide an infrastructure for Internet secure communications. ISAKMP, designed by the National Security Agency (NSA) and described in RFC , is a framework for key management and security associations, independent of the key generation and cryptographic algorithms actually employed. The OAKLEY Key Determination Protocol, described in RFC , is a key determination and distribution protocol using a variation of Diffie-Hellman.
KerberosA secret key encryption and authentication system, designed to authenticate requests for network resources within a user domain rather than to authenticate messages. Kerberos also uses a trusted third-party approach; a client communications with the Kerberos server to obtain "credentials" so that it may access services at the application server. Kerberos V4 used DES to generate keys and encrypt messages; Kerberos V5 uses DES and other schemes for key generation.

Microsoft added support for Kerberos V5 &#; with some proprietary extensions &#; in Windows Active Directory. There are many Kerberos articles posted at Microsoft's Knowledge Base, notably "Kerberos Explained."
Keyed-Hash Message Authentication Code (HMAC)A message authentication scheme based upon secret key cryptography and the secret key shared between two parties rather than public key methods. Described in FIPS PUB and RFC (See Section below for details on HMAC operation.)
Message Digest Cipher (MDC)Invented by Peter Gutman, MDC turns a one-way hash function into a block cipher.
MIME Object Security Services (MOSS)Designed as a successor to PEM to provide PEM-based security services to MIME messages. Described in RFC Never widely implemented and now defunct.
Mujahedeen SecretsA Windows GUI, PGP-like cryptosystem. Developed by supporters of Al-Qaeda, the program employs the five finalist AES algorithms, namely, MARS, RC6, Rijndael, Serpent, and Twofish. Also described in Inspire Magazine, Issue 1, pp. and Inspire Magazine, Issue 2, pp. Additional related information can also be found in "How Al-Qaeda Uses Encryption Post-Snowden (Part 2)."
New European Schemes for Signatures, Integrity and Encryption (NESSIE)NESSIE was an independent project meant to augment the work of NIST during the AES adoption process by putting out an open call for new cryptographic primitives. The NESSIE project ran from about While several new block ciper, PKC, MAC, and digital signature algorithms were found during the NESSIE process, no new stream cipher survived cryptanalysis. As a result, the ECRYPT Stream Cipher Project (eSTREAM) was created.
NSA Suite B CryptographyAn NSA standard for securing information at the SECRET level. Defines use of:
  • Advanced Encryption Standard (AES) with key sizes of and bits, per FIPS PUB for encryption
  • The Ephemeral Unified Model and the One-Pass Diffie Hellman (referred to as ECDH) using the curves with and bit prime moduli, per NIST Special Publication A for key exchange
  • Elliptic Curve Digital Signature Algorithm (ECDSA) using the curves with and bit prime moduli, per FIPS PUB for digital signatures
  • Secure Hash Algorithm (SHA) using and bits, per FIPS PUB for hashing

RFC describes Suite B Cryptographic Suites for Secure Shell (SSH) and RFC describes Suite B Cryptographic Suites for Secure IP (IPsec).

RFC reclassifies the RFCs related to the Suite B cryptographic algorithms as Historic, and it discusses the reasons for doing so.

Pretty Good Privacy (PGP)A family of cryptographic routines for e-mail, file, and disk encryption developed by Philip Zimmermann. PGP x uses RSA for key management and digital signatures, IDEA for message encryption, and MD5 for computing the message's hash value; more information can also be found in RFC PGP 5.x (formerly known as "PGP 3") uses Diffie-Hellman/DSS for key management and digital signatures; IDEA, CAST, or 3DES for message encryption; and MD5 or SHA for computing the message's hash value. OpenPGP, described in RFC , is an open definition of security software based on PGP 5.x. The GNU Privacy Guard (GPG) is a free software version of OpenPGP.

(See more detail about PGP below in Section )

Privacy Enhanced Mail (PEM)An IETF standard for secure electronic mail over the Internet, including provisions for encryption (DES), authentication, and key management (DES, RSA). Developed by the IETF but never widely used. Described in the following RFCs:
  • RFC Part I, Message Encryption and Authentication Procedures
  • RFC Part II, Certificate-Based Key Management
  • RFC Part III, Algorithms, Modes, and Identifiers
  • RFC Part IV, Key Certification and Related Services
Private Communication Technology (PCT)Developed by Microsoft for secure communication on the Internet. PCT supported Diffie-Hellman, Fortezza, and RSA for key establishment; DES, RC2, RC4, and triple-DES for encryption; and DSA and RSA message signatures. Never widely used; superceded by SSL and TLS.
Secure Electronic Transaction (SET)A communications protocol for securing credit card transactions, developed by MasterCard and VISA, in cooperation with IBM, Microsoft, RSA, and other companies. Merged two other protocols: Secure Electronic Payment Protocol (SEPP), an open specification for secure bank card transactions over the Internet developed by CyberCash, GTE, IBM, MasterCard, and Netscape; and Secure Transaction Technology (STT), a secure payment protocol developed by Microsoft and Visa International. Supports DES and RC4 for encryption, and RSA for signatures, key exchange, and public key encryption of bank card numbers. SET V is described in Book 1, Book 2, and Book 3. SET has been superceded by SSL and TLS.
Secure Hypertext Transfer Protocol (S-HTTP)An extension to HTTP to provide secure exchange of documents over the World Wide Web. Supported algorithms include RSA and Kerberos for key exchange, DES, IDEA, RC2, and Triple-DES for encryption. Described in RFC S-HTTP was never as widely used as HTTP over SSL (https).
Secure Multipurpose Internet Mail Extensions (S/MIME)An IETF secure e-mail scheme superceding PEM, and adding digital signature and encryption capability to Internet MIME messages. S/MIME Version is described in RFCs and , and employs the Cryptographic Message Syntax described in RFCs and

(More detail about S/MIME can be found below in Section )
Secure Sockets Layer (SSL)Developed in by Netscape Communications to provide application-independent security and privacy over the Internet. SSL is designed so that protocols such as HTTP, FTP (File Transfer Protocol), and Telnet can operate over it transparently. SSL allows both server authentication (mandatory) and client authentication (optional). RSA is used during negotiation to exchange keys and identify the actual cryptographic algorithm (DES, IDEA, RC2, RC4, or 3DES) to use for the session. SSL also uses MD5 for message digests and X public key certificates. SSL was found to be breakable soon after the IETF announced formation of group to work on TLS and RFC specifically prohibits the use of SSL v by TLS clients. SSL version is described in RFC All versions of SSL are now deprecated in favor of TLS; TLS v is sometimes referred to as "SSL v"

(More detail about SSL can be found below in Section )
Server Gated Cryptography (SGC)Microsoft extension to SSL that provided strong encryption for online banking and other financial applications using RC2 (bit key), RC4 (bit key), DES (bit key), or 3DES (equivalent of bit key). Use of SGC required an Windows NT Server running Internet Information Server (IIS) with a valid SGC certificate. SGC was available in bit Windows versions of Internet Explorer (IE) ; support for Mac, Unix, and bit Windows versions of IE was planned, but never materialized, and SGC was made moot when browsers started to ship with bit encryption.
ShangMi (SM) Cipher SuitesA suite of authentication, encryption, and hash algorithms from the People's Republic of China.
  • SM2 Cryptography Algorithm: A public key crypto scheme based on elliptic curves. An overview of the specification, in Chinese, can be found in GM/T Additional specifications can be found in:
  • SM3 Cryptographic Hash Algorithm: A hash algorithm operating on bit blocks to produce a bit hash value. Described in GB/T
  • SM4 Block Cipher Algorithm: A Feistel block cipher algorithm with a block length and key length of bits, and 32 rounds. Described in GB/T
An application of the ShangMi Cipher Suites in TLS can be found in RFC
Signal ProtocolA protocol for providing end-to-end encryption for voice calls, video calls, and instant messaging (including group chats). Employing a combination of AES, ECC, and HMAC algorithms, it offers such features as confidentiality, integrity, authentication, forward/future secrecy, and message repudiation. Signal is particularly interesting because of its lineage and widespread use. The Signal Protocol's earliest versions were known as TextSecure, first developed by Open Whisper Systems in TextSecure itself was based on a protocol called Off-the-Record (OTR) Messaging, designed as an improvement over OpenPGP and S/MIME. TextSecure v2 () introduced a scheme called the Axolotl Ratchet for key exchange and added additional communication features. After subsequent iterations improving key management (and the renaming of the key exchange protocol to Double Ratchet), additional cryptographic primitives, and the addition of an encrypted voice calling application (RedPhone), TextSecure was renamed Signal Protocol in The Ratchet key exchange algorithm is at the heart of the power of this system. Most messaging apps employ the users' public and private keys; the weakness here is that if the phone falls into someone else's hands, all of the messages on the device &#; including deleted messages &#; can be decrypted. The Ratchet algorithm generates a set of so-called "temporary keys" for each user, based upon that user's public/private key pair. When two users exchange messages, the Signal protocol creates a secret key by combining the temporary and permanent pairs of public and private keys for both users. Each message is assigned its own secret key. Because the generation of the secret key requires access to both users' private keys, it exists only on their two devices. The Signal Protocol is/has been employed in:
  • WhatsApp (introduced )
  • G Data Software's Secure Chat (introduced ; service discontinued )
  • Google's Allo app (introduced ; discontinued in favor of Messages app, )
  • Facebook Messenger (introduced )
  • Skype's Private Conversations mode (introduced )
  • All of Google's Rich Communication Services (RCS) on Android systems (introduced )
A reasonably good writeup of the protocol can be found in "Demystifying the Signal Protocol for End-to-End Encryption (E2EE)" by Kozhukhovskaya, Mora, and Wong ().
Simple Authentication and Security Layer (SASL)A framework for providing authentication and data security services in connection-oriented protocols (a la TCP), described in RFC It provides a structured interface and allows new protocols to reuse existing authentication mechanisms and allows old protocols to make use of new mechanisms.

It has been common practice on the Internet to permit anonymous access to various services, employing a plain-text password using a user name of "anonymous" and a password of an email address or some other identifying information. New IETF protocols disallow plain-text logins. The Anonymous SASL Mechanism (RFC ) provides a method for anonymous logins within the SASL framework.
Simple Key-Management for Internet Protocol (SKIP)Key management scheme for secure IP communication, specifically for IPsec, and designed by Aziz and Diffie. SKIP essentially defines a public key infrastructure for the Internet and even uses X certificates. Most public key cryptosystems assign keys on a per-session basis, which is inconvenient for the Internet since IP is connectionless. Instead, SKIP provides a basis for secure communication between any pair of Internet hosts. SKIP can employ DES, 3DES, IDEA, RC2, RC5, MD5, and SHA As it happened, SKIP was not adopted for IPsec; IKE was selected instead.
SM9Chinese Standard GM/T SM9 () is the Chinese national standard for Identity Based Cryptography. SM9 comprises three cryptographic algorithms, namely the Identity Based Digital Signature Algorithm, Identity Based Key Agreement Algorithm, and Identity Based Key Encapsulation Algorithm (allowing one party to securely send a symmetric key to another party). The SM9 scheme is also described in The SM9 Cryptographic Schemes (Z. Cheng).
TelegramTelegram, launched in , is a cloud-based instant messaging and voice over IP (VoIP) service, with client app software available for all major computer and mobile device operating systems. Telegram allows users to exchange messages, photos, videos, etc., and supplies end-to-end encryption using a protocol called MTProto. stickers, audio and files of any type. MTProto employs bit AES, bit RSA, and Diffie-Hellman key exchange. There have been several contriversies with Telegram, not the least of which has to do with the nationality of the founders and the true location of the business, as well as some operation issues. From a cryptological viewpoint, however, one cautionary tale can be found in "On the CCA (in)security of MTProto" (Jakobsen & Orlandi, ), who describe some of the crypto weaknesses of the protocol; specifically, that "MTProto does not satisfy the definitions of authenticated encryption (AE) or indistinguishability under chosen-ciphertext attack (IND-CCA)" (p. 1).
Transmission Control Protocol (TCP) encryption (tcpcrypt)As of , the majority of Internet TCP traffic is not encrypted. The two primary reasons for this are (1) many legacy protocols have no mechanism with which to employ encryption (e.g., without a command such as STARTSSL, the protocol cannot invoke use of any encryption) and (2) many legacy applications cannot be upgraded, so no new encryption can be added. The response from the IETF's TCP Increased Security Working Group was to define a transparent way within the transport layer (i.e., TCP) with which to invoke encryption. The TCP Encryption Negotiation Option (TCP-ENO) addresses these two problems with an out-of-band, fully backward-compatible TCP option with which to negotiate use of encryption. TCP-ENO is described in RFC and tcpcrypt, an encryption protocol to protect TCP streams, is described in RFC
Transport Layer Security (TLS)TLS v is an IETF specification (RFC ) intended to replace SSL v TLS v employs Triple-DES (secret key cryptography), SHA (hash), Diffie-Hellman (key exchange), and DSS (digital signatures). TLS v was vulnerable to attack and updated by v (RFC ), which is now classified as an HISTORIC specification. TLS v was replaced by TLS v (RFC ) and, subsequently, by v (RFC ).

TLS is designed to operate over TCP. The IETF developed the Datagram Transport Layer Security (DTLS) protocol to operate over UDP. DTLS v is described in RFC

(See more detail about TLS below in Section )
TrueCryptOpen source, multi-platform cryptography software that can be used to encrypt a file, partition, or entire disk. One of TrueCrypt's more interesting features is that of plausible deniability with hidden volumes or hidden operating systems. The original Web site, storycall.us, suddenly went dark in May The current fork of TrueCrypt is VeraCrypt.

(See more detail about TrueCrypt below in Section )
XITU-T recommendation for the format of certificates for the public key infrastructure. Certificates map (bind) a user identity to a public key. The IETF application of X certificates is documented in RFC An Internet X Public Key Infrastructure is further defined in RFC (Certificate Management Protocols) and RFC (Certificate Policy and Certification Practices Framework).

Password Protection

Nearly all modern multiuser computer and network operating systems employ passwords at the very least to protect and authenticate users accessing computer and/or network resources. But passwords are not typically kept on a host or server in plaintext, but are generally encrypted using some sort of hash scheme.

A) /etc/passwd file root:Jbw6BwE4XoUHoroot:/root:/bin/bash carol:FM5ikbQt1KCarol Monaghan:/home/carol:/bin/bash alex:LqAi7Mdyg/HcQAlex Insley:/home/alex:/bin/bash gary:FkJXupRyFqY4sGary Kessler:/home/gary:/bin/bash todd:edGqQUAaGv7gTodd Pritsky:/home/todd:/bin/bash josh:FiH0ONcjPut1gJoshua Kessler:/home/webroot:/bin/bash B.1) /etc/passwd file (with shadow passwords) root:xroot:/root:/bin/bash carol:xCarol Monaghan:/home/carol:/bin/bash alex:xAlex Insley:/home/alex:/bin/bash gary:xGary Kessler:/home/gary:/bin/bash todd:xTodd Pritsky:/home/todd:/bin/bash josh:xJoshua Kessler:/home/webroot:/bin/bash B.2) /etc/shadow file root:AGFw$1$P4u/uhLK$storycall.us35rlu65WlfCzq carol:kjHaN%35a8xMM8a/0kMl1?fwtLAM.K&kw alex:1$1KKmfTy0a7#storycall.us9a8H71lkwn/.hH22a gary:9ajlknknKJHjhnuypnAIJKL$storycall.us toddPOJ90uab6.k$klPqMt%alMlprWqu6$ josh:Awmqpsui*pjnsnJJK%aappaMpQo

FIGURE 8: Sample entries in Unix/Linux password files.

Unix/Linux, for example, uses a well-known hash via its crypt() function. Passwords are stored in the /etc/passwd file (Figure 8A); each record in the file contains the username, hashed password, user's individual and group numbers, user's name, home directory, and shell program; these fields are separated by colons (:). Note that each password is stored as a byte string. The first two characters are actually a salt, randomness added to each password so that if two users have the same password, they will still be encrypted differently; the salt, in fact, provides a means so that a single password might have different encryptions. The remaining 11 bytes are the password hash, calculated using DES.

As it happens, the /etc/passwd file is world-readable on Unix systems. This fact, coupled with the weak encryption of the passwords, resulted in the development of the shadow password system where passwords are kept in a separate, non-world-readable file used in conjunction with the normal password file. When shadow passwords are used, the password entry in /etc/passwd is replaced with a "*" or "x" (Figure 8B.1) and the MD5 hash of the passwords are stored in /etc/shadow along with some other account information (Figure 8B.2).

Windows NT uses a similar scheme to store passwords in the Security Access Manager (SAM) file. In the NT case, all passwords are hashed using the MD4 algorithm, resulting in a bit (byte) hash value (they are then obscured using an undocumented mathematical transformation that was a secret until distributed on the Internet). The password password, for example, might be stored as the hash value (in hexadecimal) b22d73c34bd4aa79c8b09f

Passwords are not saved in plaintext on computer systems precisely so they cannot be easily compromised. For similar reasons, we don't want passwords sent in plaintext across a network. But for remote logon applications, how does a client system identify itself or a user to the server? One mechanism, of course, is to send the password as a hash value and that, indeed, may be done. A weakness of that approach, however, is that an intruder can grab the password off of the network and use an off-line attack (such as a dictionary attack where an attacker takes every known word and encrypts it with the network's encryption algorithm, hoping eventually to find a match with a purloined password hash). In some situations, an attacker only has to copy the hashed password value and use it later on to gain unauthorized entry without ever learning the actual password.

An even stronger authentication method uses the password to modify a shared secret between the client and server, but never allows the password in any form to go across the network. This is the basis for the Challenge Handshake Authentication Protocol (CHAP), the remote logon process used by Windows NT.

As suggested above, Windows NT passwords are stored in a security file on a server as a byte hash value. In truth, Windows NT stores two hashes; a weak hash based upon the old LAN Manager (LanMan) scheme and the newer NT hash. When a user logs on to a server from a remote workstation, the user is identified by the username, sent across the network in plaintext (no worries here; it's not a secret anyway!). The server then generates a bit random number and sends it to the client (also in plaintext). This number is the challenge.

Using the LanMan scheme, the client system then encrypts the challenge using DES. Recall that DES employs a bit key, acts on a bit block of data, and produces a bit output. In this case, the bit data block is the random number. The client actually uses three different DES keys to encrypt the random number, producing three different bit outputs. The first key is the first seven bytes (56 bits) of the password's hash value, the second key is the next seven bytes in the password's hash, and the third key is the remaining two bytes of the password's hash concatenated with five zero-filled bytes. (So, for the example above, the three DES keys would be b22d73c34, bd4aa79c8b0, and 9f) Each key is applied to the random number resulting in three bit outputs, which comprise the response. Thus, the server's 8-byte challenge yields a byte response from the client and this is all that would be seen on the network. The server, for its part, does the same calculation to ensure that the values match.

There is, however, a significant weakness to this system. Specifically, the response is generated in such a way as to effectively reduce byte hash to three smaller hashes, of length seven, seven, and two, respectively. Thus, a password cracker has to break at most a 7-byte hash. One Windows NT vulnerability test program that I used in the past reported passwords that were "too short," defined as "less than 8 characters." When I asked how the program knew that passwords were too short, the software's salespeople suggested to me that the program broke the passwords to determine their length. This was, in fact, not the case at all; all the software really had to do was to look at the last eight bytes of the Windows NT LanMan hash to see that the password was seven or fewer characters.

Consider the following example, showing the LanMan hash of two different short passwords (take a close look at the last 8 bytes):

AA: 89D42A44EAAAAD3BBEE
AAA: 1C3A2B6DAAAD3BBEE

Note that the NT hash provides no such clue:

AA: CFBE79C8FD99FE7AAD8
AAA: 6B6E0FB2EDBC73B5BFB77

It is worth noting that the discussion above describes the Microsoft version of CHAP, or MS-CHAP (MS-CHAPv2 is described in RFC ). MS-CHAP assumes that it is working with hashed values of the password as the key to encrypting the challenge. More traditional CHAP (RFC ) assumes that it is starting with passwords in plaintext. The relevance of this observation is that a CHAP client, for example, cannot be authenticated by an MS-CHAP server; both client and server must use the same CHAP version.

Diffie-Hellman Key Exchange

Diffie and Hellman introduced the concept of public key cryptography. The mathematical "trick" of Diffie-Hellman key exchange is that it is relatively easy to compute exponents compared to computing discrete logarithms. Diffie-Hellman allows two parties &#; the ubiquitous Alice and Bob &#; to generate a secret key; they need to exchange some information over an unsecure communications channel to perform the calculation but an eavesdropper cannot determine the shared secret key based upon this information.

Diffie-Hellman works like this. Alice and Bob start by agreeing on a large prime number, N. They also have to choose some number G so that G<N.

There is actually another constraint on G, namely that it must be primitive with respect to N. Primitive is a definition that is a little beyond the scope of our discussion but basically G is primitive to N if the set of N-1 values of Gi mod N for i = (1,N-1) are all different. As an example, 2 is not primitive to 7 because the set of powers of 2 from 1 to 6, mod 7 (i.e., 21 mod 7, 22 mod 7, , 26 mod 7) = {2,4,1,2,4,1}. On the other hand, 3 is primitive to 7 because the set of powers of 3 from 1 to 6, mod 7 = {3,2,6,4,5,1}.

(The definition of primitive introduced a new term to some readers, namely mod. The phrase x mod y (and read as written!) means "take the remainder after dividing x by y." Thus, 1 mod 7 = 1, 9 mod 6 = 3, and 8 mod 8 = 0. Read more about the modulo function in the appendix.)

Anyway, either Alice or Bob selects N and G; they then tell the other party what the values are. Alice and Bob then work independently (Figure 9):

Alice

  1. Choose a large random number, XA < N. This is Alice's private key.
  2. Compute YA = GXA mod N. This is Alice's public key.
  3. Exchange public key with Bob.
  4. Compute KA = YBXA mod N
Bob

  1. Choose a large random number, XB < N. This is Bob's private key.
  2. Compute YB = GXB mod N. This is Bob's public key.
  3. Exchange public key with Alice.
  4. Compute KB = YAXB mod N
FIGURE 9: Diffie-Hellman key exchange model.

Note that XA and XB are kept secret while YA and YB are openly shared; these are the private and public keys, respectively. Based on their own private key and the public key learned from the other party, Alice and Bob have computed their secret keys, KA and KB, respectively, which are equal to GXAXB mod N.

Perhaps a small example will help here. Although Alice and Bob will really choose large values for N and G, I will use small values for example only; let's use N=7 and G=3, as shown in Figure

Alice

  1. Choose private key; XA = 2
  2. Compute public key; YA = 32 mod 7 = 2
  3. Exchange public key with Bob
  4. KA = YBXA mod N = 62 mod 7 = 1
Bob

  1. Choose private key; XB = 3
  2. Compute public key; YB = 33 mod 7 = 6
  3. Exchange public key with Alice
  4. KB = YAXB mod N = 23 mod 7 = 1
FIGURE Diffie-Hellman key exchange example.

In this example, then, Alice and Bob will both find the secret key 1 which is, indeed, 36 mod 7 (i.e., GXAXB = 32x3). If an eavesdropper (Eve) was listening in on the information exchange between Alice and Bob, she would learn G, N, YA, and YB which is a lot of information but insufficient to compromise the key; as long as XA and XB remain unknown, K is safe. As stated above, calculating Y = GX is a lot easier than finding X = logG Y.


A short digression on modulo arithmetic. In the paragraph above, we noted that 36 mod 7 = 1. This can be confirmed, of course, by noting that:

36 = = *7 + 1

There is a nice property of modulo arithmetic, however, that makes this determination a little easier, namely: (a mod x)(b mod x) = (ab mod x). Therefore, one possible shortcut is to note that 36 = (33)(33). Therefore, 36 mod 7 = (33 mod 7)(33 mod 7) = (27 mod 7)(27 mod 7) = 6*6 mod 7 = 36 mod 7 = 1.


Diffie-Hellman can also be used to allow key sharing amongst multiple users. Note again that the Diffie-Hellman algorithm is used to generate secret keys, not to encrypt and decrypt messages.

RSA Public Key Cryptography

Unlike Diffie-Hellman, RSA can be used for key exchange as well as digital signatures and the encryption of small blocks of data. Today, RSA is primarily used to encrypt the session key used for secret key encryption (message integrity) or the message's hash value (digital signature). RSA's mathematical hardness comes from the ease in calculating large numbers and the difficulty in finding the prime factors of those large numbers. Although employed with numbers using hundreds of digits, the math behind RSA is relatively straight-forward.

To create an RSA public/private key pair, here are the basic steps:

  1. Choose two prime numbers, p and q. From these numbers you can calculate the modulus, n = pq.
  2. Select a third number, e, that is relatively prime to (i.e., it does not divide evenly into) the product (p-1)(q-1). The number e is the public exponent.
  3. Calculate an integer d from the quotient (ed-1)/[(p-1)(q-1)]. The number d is the private exponent.

The public key is the number pair (n,e). Although these values are publicly known, it is computationally infeasible to determine d from n and e if p and q are large enough.

To encrypt a message, M, with the public key, create the ciphertext, C, using the equation:

The receiver then decrypts the ciphertext with the private key using the equation:

Now, this might look a bit complex and, indeed, the mathematics does take a lot of computer power given the large size of the numbers; since p and q may be digits (decimal) or more, d and e will be about the same size and n may be over digits. Nevertheless, a simple example may help. In this example, the values for p, q, e, and d are purposely chosen to be very small and the reader will see exactly how badly these values perform, but hopefully the algorithm will be adequately demonstrated:

  1. Select p=3 and q=5.
  2. The modulus n = pq =
  3. The value e must be relatively prime to (p-1)(q-1) = (2)(4) = 8. Select e=
  4. The value d must be chosen so that (ed-1)/[(p-1)(q-1)] is an integer. Thus, the value (11d-1)/[(2)(4)] = (11d-1)/8 must be an integer. Calculate one possible value, d=3.
  5. Let's suppose that we want to send a message &#; maybe a secret key &#; that has the numeric value of 7 (i.e., M=7). [More on this choice below.]
  6. The sender encrypts the message (M) using the public key value (e,n)=(11,15) and computes the ciphertext (C) with the formula C = 711 mod 15 =  mod 15 =
  7. The receiver decrypts the ciphertext using the private key value (d,n)=(3,15) and computes the plaintext with the formula M = 133 mod 15 =  mod 15 = 7.

I choose this trivial example because the value of n is so small (in particular, the value M cannot exceed n). But here is a more realistic example using larger d, e, and n values, as well as a more meaningful message; thanks to Barry Steyn for permission to use values from his How RSA Works With Examples page.

Let's say that we have chosen p and q so that we have the following value for n:





Let's also suppose that we have selected the public key, e, and private key, d, as follows:





Now suppose that our message (M) is the character string "attack at dawn" which has the numeric value (after converting the ASCII characters to a bit string and interpreting that bit string as a decimal number) of

The encryption phase uses the formula C = Me mod n, so C has the value:





The decryption phase uses the formula M = Cd mod n, so M has the value that matches our original plaintext:

This more realistic example gives just a clue as to how large the numbers are that are used in the real world implementations. RSA keylengths of and bits are considered to be pretty weak. The minimum suggested RSA key is bits; and bits are even better.

As an aside, Adam Back (storycall.us~adam/) wrote a two-line Perl script to implement RSA. It employs dc, an arbitrary precision arithmetic package that ships with most UNIX systems:

print pack"C*",split/\D+/,`echo "16iII*o\U@{$/=$z;[(pop,pop,unpack"H*",<> )]}\EsMsKsN0[lN*1lK[d2%Sa2/d0<X+d*lMLa^*lN%0]dsXx++lMlN/dsM0<J]dsJxp" dc`

DES, Breaking DES, and DES Variants

The Data Encryption Standard (DES) started life in the mids, adopted by the National Bureau of Standards (NBS) [now the National Institute of Standards and Technology (NIST)] as Federal Information Processing Standard 46 (FIPS PUB ) and by the American National Standards Institute (ANSI) as X

As mentioned earlier, DES uses the Data Encryption Algorithm (DEA), a secret key block-cipher employing a bit key operating on bit blocks. FIPS PUB 81 describes four modes of DES operation: Electronic Codebook (ECB), Cipher Block Chaining (CBC), Cipher Feedback (CFB), and Output Feedback (OFB). Despite all of these options, ECB is the most commonly deployed mode of operation.

NIST finally declared DES obsolete in , and withdrew FIPS PUB , 74, and 81 (Federal Register, July 26, , 69(), ). Although other block ciphers have replaced DES, it is still interesting to see how DES encryption is performed; not only is it sort of neat, but DES was the first crypto scheme commonly seen in non-governmental applications and was the catalyst for modern "public" cryptography and the first public Feistel cipher. DES still remains in many products &#; and cryptography students and cryptographers will continue to study DES for years to come.

DES Operational Overview

DES uses a bit key. In fact, the bit key is divided into eight 7-bit blocks and an 8th odd parity bit is added to each block (i.e., a "0" or "1" is added to the block so that there are an odd number of 1 bits in each 8-bit block). By using the 8 parity bits for rudimentary error detection, a DES key is actually 64 bits in length for computational purposes although it only has 56 bits worth of randomness, or entropy (See Section A.3 for a brief discussion of entropy and information theory).

FIGURE DES enciphering algorithm.

DES then acts on bit blocks of the plaintext, invoking 16 rounds of permutations, swaps, and substitutes, as shown in Figure The standard includes tables describing all of the selection, permutation, and expansion operations mentioned below; these aspects of the algorithm are not secrets. The basic DES steps are:

  1. The bit block to be encrypted undergoes an initial permutation (IP), where each bit is moved to a new bit position; e.g., the 1st, 2nd, and 3rd bits are moved to the 58th, 50th, and 42nd position, respectively.

  2. The bit permuted input is divided into two bit blocks, called left and right, respectively. The initial values of the left and right blocks are denoted L0 and R0.

  3. There are then 16 rounds of operation on the L and R blocks. During each iteration (where n ranges from 1 to 16), the following formulae apply:

      Ln = Rn-1
      Rn = Ln-1 ⊕ f(Rn-1,Kn)

    At any given step in the process, then, the new L block value is merely taken from the prior R block value. The new R block is calculated by taking the bit-by-bit exclusive-OR (XOR) of the prior L block with the results of applying the DES cipher function, f, to the prior R block and Kn. (Kn is a bit value derived from the bit DES key. Each round uses a different 48 bits according to the standard's Key Schedule algorithm.)

    The cipher function, f, combines the bit R block value and the bit subkey in the following way. First, the 32 bits in the R block are expanded to 48 bits by an expansion function (E); the extra 16 bits are found by repeating the bits in 16 predefined positions. The bit expanded R-block is then ORed with the bit subkey. The result is a bit value that is then divided into eight 6-bit blocks. These are fed as input into 8 selection (S) boxes, denoted S1,,S8. Each 6-bit input yields a 4-bit output using a table lookup based on the 64 possible inputs; this results in a bit output from the S-box. The 32 bits are then rearranged by a permutation function (P), producing the results from the cipher function.

  4. The results from the final DES round &#; i.e., L16 and R16 &#; are recombined into a bit value and fed into an inverse initial permutation (IP-1). At this step, the bits are rearranged into their original positions, so that the 58th, 50th, and 42nd bits, for example, are moved back into the 1st, 2nd, and 3rd positions, respectively. The output from IP-1 is the bit ciphertext block.

Consider this example using DES in CBC mode with the following bit key and input:

    Key: = 0xDB6C1A

    Input character string (ASCII/IA5): +
    Input string (hex): 0x2BD

    Output string (hex): 0xCBB2E9FD3AD90DE2B92C6BBB6CAC43E1AFA6
    Output character string (BASE64): mBLLYgsun9OtkN4rksa7tsUnU6xD4a+m

Observe that we start with a byte input message. DES acts on eight bytes at a time, so this message is padded to 24 bytes and provides three "inputs" to the cipher algorithm (we don't see the padding here; it is appended by the DES code). Since we have three input blocks, we get 24 bytes of output from the three bit (eight byte) output blocks.

If you want to test this, a really good free, online DES calculator hosted by the Information Security Group at University College London. An excellent step-by-step example of DES can also be found at J. Orlin Grabbe's The DES Algorithm Illustrated page.


NOTE: You'll notice that the output above is shown in BASE BASE64 is a character alphabet &#; i.e., a six-bit character code composed of upper- and lower-case letters, the digits , and a few punctuation characters &#; that is commonly used as a way to display binary data. A byte has eight bits, or values, but not all ASCII characters are defined and/or printable. BASE64, simply, takes a binary string (or file), divides it into six-bit blocks, and translates each block into a printable character. More information about BASE64 can be found at my BASE64 Alphabet page or at Wikipedia.

Breaking DES

The mainstream cryptographic community has long held that DES's bit key was too short to withstand a brute-force attack from modern computers. Remember Moore's Law: computer power doubles every 18 months. Given that increase in power, a key that could withstand a brute-force guessing attack in could hardly be expected to withstand the same attack a quarter century later.

DES is even more vulnerable to a brute-force attack because it is often used to encrypt words, meaning that the entropy of the bit block is, effectively, greatly reduced. That is, if we are encrypting random bit streams, then a given byte might contain any one of 28 () possible values and the entire bit block has 264, or about quintillion, possible values. If we are encrypting words, however, we are most likely to find a limited set of bit patterns; perhaps 70 or so if we account for upper and lower case letters, the numbers, space, and some punctuation. This means that only about &#; of the bit combinations of a given byte are likely to occur.

Despite this criticism, the U.S. government insisted throughout the mids that bit DES was secure and virtually unbreakable if appropriate precautions were taken. In response, RSA Laboratories sponsored a series of cryptographic challenges to prove that DES was no longer appropriate for use.

DES Challenge I was launched in March It was completed in 84 days by R. Verser in a collaborative effort using thousands of computers on the Internet.

The first DES Challenge II lasted 40 days in early This problem was solved by storycall.us, a worldwide distributed computing network using the spare CPU cycles of computers around the Internet (participants in storycall.us's activities load a client program that runs in the background, conceptually similar to the SETI @Home "Search for Extraterrestrial Intelligence" project). The storycall.us systems were checking 28 billion keys per second by the end of the project.

The second DES Challenge II lasted less than 3 days. On July 17, , the Electronic Frontier Foundation (EFF) announced the construction of hardware that could brute-force a DES key in an average of days. Called Deep Crack, the device could check 90 billion keys per second and cost only about $, including design (it was erroneously and widely reported that subsequent devices could be built for as little as $50,). Since the design is scalable, this suggests that an organization could build a DES cracker that could break bit keys in an average of a day for as little as $1,, Information about the hardware design and all software can be obtained from the EFF.

The DES Challenge III, launched in January , was broken is less than a day by the combined efforts of Deep Crack and storycall.us This is widely considered to have been the final nail in DES's coffin.

The Deep Crack algorithm is actually quite interesting. The general approach that the DES Cracker Project took was not to break the algorithm mathematically but instead to launch a brute-force attack by guessing every possible key. A bit key yields 256, or about 72 quadrillion, possible values. So the DES cracker team looked for any shortcuts they could find! First, they assumed that some recognizable plaintext would appear in the decrypted string even though they didn't have a specific known plaintext block. They then applied all 256 possible key values to the bit block (I don't mean to make this sound simple!). The system checked to see if the decrypted value of the block was "interesting," which they defined as bytes containing one of the alphanumeric characters, space, or some punctuation. Since the likelihood of a single byte being "interesting" is about &#;, then the likelihood of the entire 8-byte stream being "interesting" is about &#;8, or 1/ (&#;16). This dropped the number of possible keys that might yield positive results to about 240, or about a trillion.

They then made the assumption that an "interesting" 8-byte block would be followed by another "interesting" block. So, if the first block of ciphertext decrypted to something interesting, they decrypted the next block; otherwise, they abandoned this key. Only if the second block was also "interesting" did they examine the key closer. Looking for 16 consecutive bytes that were "interesting" meant that only 224, or 16 million, keys needed to be examined further. This further examination was primarily to see if the text made any sense. Note that possible "interesting" blocks might be 1hJ5&aB7 or DEPOSITS; the latter is more likely to produce a better result. And even a slow laptop today can search through lists of only a few million items in a relatively short period of time. (Interested readers are urged to read Cracking DES and EFF's Cracking DES page.)

It is well beyond the scope of this paper to discuss other forms of breaking DES and other codes. Nevertheless, it is worth mentioning a couple of forms of cryptanalysis that have been shown to be effective against DES. Differential cryptanalysis, invented in by E. Biham and A. Shamir (of RSA fame), is a chosen-plaintext attack. By selecting pairs of plaintext with particular differences, the cryptanalyst examines the differences in the resultant ciphertext pairs. Linear plaintext, invented by M. Matsui, uses a linear approximation to analyze the actions of a block cipher (including DES). Both of these attacks can be more efficient than brute force.

DES Variants

Once DES was "officially" broken, several variants appeared. But none of them came overnight; work at hardening DES had already been underway. In the early s, there was a proposal to increase the security of DES by effectively increasing the key length by using multiple keys with multiple passes. But for this scheme to work, it had to first be shown that the DES function is not a group, as defined in mathematics. If DES was a group, then we could show that for two DES keys, X1 and X2, applied to some plaintext (P), we can find a single equivalent key, X3, that would provide the same result; i.e.,

EX2(EX1(P)) = EX3(P)

where EX(P) represents DES encryption of some plaintext P using DES key X. If DES were a group, it wouldn't matter how many keys and passes we applied to some plaintext; we could always find a single bit key that would provide the same result.

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Источник: [storycall.us]

Gold Utils #

Looking for old abandonware warez CD ISO's - If you have any not in my collection please contact me (pascal_of_irate @ hotmail . com). I can remove any copy protections from them (if required) and repost cracked versions for the community to enjoy.


I am especially interested in CD's from the likes of Blobby International, Playdoh, Voodoo, Ghost, Tango, Delta, USA, Gold, Redhot, Jurassic, Pepsi, Alkey, Capaccino, Coke, Delta, Total, Razor, Xenon etc, but also any others from this era.


Please see our special requests as the bottom of this page.




Gold Utils 3D Charge V 3D TextBeauty v + Crack File Pro LAN SUITE a v Serial Number: LSAH60I or LSAH60I Abyss v + KeyGen Advanced Maillist Verify v Regged (C) Elcom Ltd. RegCode: AMVQMVZY Advanced Registry Tracer v (C) Elcom Ltd Serial Number: ARTPHQNS Advertisment Wizard UserName: maximum Password: 2ZLWILR AlphaNotes (C) G Pearson + KeyGen Animated GIFSaver v + KeyGen Arles Image Web Page Creator v (C) Digital Dutch + Crack File Armadillo v (C) Silicon Realms + Crack File BR's PhotoArchiver + Crack File Boot/Partition Repair v Read the *.nfo file for install help. Buddy Phone d Button Studio v (C) by Interkodex + KeyGen Cool Sheets (C) Lamantine Software Company + KeyGen CosyDat Ras Manager v (C) CosyDat Name: naManaX for Blizzard Serial: Create A Saver v (C) Howies Shareware Key: DirectX 8 Build for Win DirectX 8 Build for Win9x Dont Panic v EZ Split v Name: Slim Shady Code: ESCR Easy Calendar v + KeyGen Easy GradeBook v + KeyGen EditorPro Suite v + KeyGen EnergySaver v (C) by Entech Taiwan + KeyGen F-Secure Anti-Virus Server v (C) F-Secure Corp. CD Key: AAAA-X72A-B52A-AAAU-CTB2 F-Secure Distributed Firewall v (C) F-Secure Corp. CD Key: AAAA-XF2A-BYXA-AAA0-H3L6 F-Secure FileCrypto v (C) F-Secure Corp. CD Key: AAAA-XG2A-BAXA-AAAVS6 F-Secure SSH Client v (C) F-Secure Corp. CD Key: F-Secure VPN Plus Client v (C) F-Secure Corp. CD Key: AAAA-X02A-BA2A-AAAT-KMG6 F-Secure VPN Plus Server v (C) F-Secure Corp. CD Key: AAAA-X52A-BC2A-AAAT-N19B FinePrint v for Win9x (C) FinePrint Software Name: archi[ga]medis Serial: ED3B-XHJH-9BXD FinePrint v for WinNT/2k (C) FinePrint Software Name: archi[ga]medis Serial: ED3B-XHJH-9BXD FinePrint Enterprise v (C) FinePrint Software Name: archi[ga]medis Serial: JNUN-3LRV-XFYM GEAR Audio v + Crack File GEAR CD Replicator v + Crack File GEAR Data v + Crack File Help Desk Analyst (C) Dennis Baggott Hard Coded Serial: tuition Hex Express v + Crack File HiClock Pro v + Crack File Hotkey Maker (C) ALD-Software + Crack File IPMonitor v + KeyGen InternetCharge Retail Intertax v Name: TheBrabo Nr: Code: Investcheck + Crack File InvestmentSpy.v (C) Quantum Axcess Jammer v (C) Homer P. Lee + KeyGen Kool Moves V With Bonus Effects Serial Number: xAAAAAA MB Soft Trap Ringer v + Crack File MERANT PVCS Version Manager CD Key: MP3 Detective v + KeyGen MP3 Detective v Upgrade MP3 Home Studio Deluxe + Crack File MP3 Navigator v + Crack Reg MP3 Tag Team v (C) Jörg LünsmannSegaGT + KeyGen Mp3 To Wave Converter v (C) Acoustica + KeyGen Mp3 Trim PRO (C) Jean Nicolle NoaXs v (C) Welshware + KeyGen Ontrack System Suite v Panopticum Tools V For Adobe After Effects Serial Number: PTA PhoneList v (C) Angstrom Software + KeyGen Photo Print v + Crack File PhotoGenetics v + Crack File PicPreview v (C) Wright Futures Inc. Name : TEAM LAXiTY Key : Picture Agent v (C) Richard Thead Polar ZIP Component (C) Polar Software Pro/Engineer I2 Datecode For WinNT (C) Ptc Inc + Crack File Pro/Engineer I2 Datecode (C) Ptc Inc Installation Intructions. Pro/Engineer Fly-Through V Datecode (C) Ptc + Crack File Pro/Engineer Fly-Through V Datecode (C) Ptc Installation Intructions. Pro/Engineer Model View V Datecode (C) Ptc + Crack File Pro/Engineer Model View V Datecode (C) Ptc Installation Intructions. SiSoft Sandra Professional Millennium Sony C5 Phone Reset And Unlock v Read *.nfo for installation info. SplitWinCL v Name: TEAM ElilA Serial: fdef3-fbb7fa Stagetools Moving Picture V For After Effects + KeyGen Stagetools Moving Picture V For Premiere + KeyGen Stagetools Moving Picture V For Rex Edit + KeyGen Stagetools Moving Picture V For Speed + KeyGen Stagetools Moving Picture VBeta For Avid + KeyGen Starburst V For Adobe Indesign Serial Number: INSBBD-4 SurfDoubler v (C) Vicomsoft ID: E-Mail: geoffrey@storycall.us AuthUser: Geoffrey Daniel SurfDoubler v (C) Vicomsoft + Crack File TelStar + Crack File Top Report ODBC Edition v (C) DaemonSoft + KeyGen Trainer + Crack File UI-View v Callsign: SEXY Name: Pookie RegNo: UK Speaking Calendar v + Crack Reg Url Spider Pro V (C) Innerprise + Crack File Voodoo Lights v (C) Sergio Duarte Vopt99 v Win9x + Crack File Weather1 v + KeyGen Web Check + Crack File WebSync (C) Andrew Fish WinHex v (C) Stefan Fleischmann Code1 : Code2 : WinRescue 98 v (C) Super Win Software Serial Number: SvetCHRISTA WinWAP v PRO Serial Number: WWF31B-F7EFD8D WindowFX (C) Stardock Serial Number: wxlt1o-x7t3-t5lb-gqb7 Winedit e + KeyGen XML Instance v (C) Extensibility Inc. Serial Number: 1FCF YTS Words Suite v + KeyGen Welcome to Gold Utils told you there would be some Gold Utils Cd`s.. here they are.. I think they might be a bit late in the posting though, I don`t havr the petrol to get to the post office hehehe.. Well, when you do get these utils CD`s there`s plenty for you lot to plough through see ya catch ya later.. bye.. gOLd
File: GOLDUTILSiso SHA1: bec84db5cdabe7ef47ff
Special request if you have any of these CD's please contact us:
  • Blobby #04, #05, #12, #15, #16, #17, #18, #19(Part 2), #20, #21, #25, #36, #40, #41, #43, #44
  • Silverado September 96 (Password: walkman)


Источник: [storycall.us]

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Pro VPNlatesthocus-focusHocus Focus,holavpnHola VPN,home-assistantHome Assistant,home-inventoryHome Inventory,honerHonerhontohonto view app,hookHook,hookshotHookshot,53hopper-debugger-serverHopper Debugger ServerhorndisHoRNDIShorosHoros – Free, open medical image viewerhoststoolHosts tool for MachotHothotswitchHotSwitchhoudahspotHoudahSpot,housepartyHouseparty,hp-eprintHP ePrinthp-primeHP Prime_01_16hstrackerHearthstone Deck Trackerhttp-toolkitHTTP ToolkithubstaffHubstaff,hue-topiaHue-topia,huginHuginhushHushhwsensorsHWSensorshydrogenHydrogenhydrus-networkhydrus-networkhypeTumult Hype,hyperHyperhyperbackupexplorerHyperBackupExplorerhyperdockHyperDocklatesthyperkeyhyperkeyhyperswitchHyperSwitchdevi1profileri1ProfileribabeliBabelibackupiBackupibackup-vieweriBackup VieweribackupbotiBackupBotibetterchargeiBetterCharge,ibm-aspera-connectIBM Aspera Connectibm-cloud-cliIBM Cloud CLIiborediBoredicabiCabicanhazshortcutiCanHazShortcuticcInternational Chess Club,icebergIcebergicefloorIceFlooricestudioicestudioicloud-controliCloud ControlicollectionsiCollections,iconizerIconizericonjarIconJar,iconsIconsicons8Icons8 App,iconscoutIconscouticonsetIconseticqICQid3-editorID3 EditoridafreeIDA FreeidagioIDAGIOidefragiDefragidisplayiDisplaylatestidriveiDrivelatestieasemusicieaseMusiciexploreriExplorer,ifunboxiFunBoxigdmIG:dmigetteriGetteriglanceiGlanceigvIntegrative Genomics Viewer (IGV)iinaIINA,iina-plusIINA+,ilok-license-manageriLok License Manager,ilspyILSpyrc2ilya-birman-typography-layoutIlya Birman Typography Layoutimage-toolImage Toolimage2iconImage2Icon,imagealphaImageAlphaimagejImageJimageminimageminimageoptimImageOptimimazingiMazing,imdoneimdoneimgotv芒果TVimmersedImmersed,imoImo MessangerimpactorImpactorinav-configuratorINAV ConfiguratorinboardInboard,indigoIndigo DomoticsinfinityInfinityinfoflowBaidu Hi,informInform6M62infrainfrainkdropInkdropinkscapeInkscapeinkyInkyinloop-qlplaygroundinloop-qlplaygroundinsoinsoinsomniaInsomniainssiderinSSIDer,8install-disk-creatorInstall Disk Creatorinstatus-outInstatus OutinsyncInsyncintegrityIntegrityintel-haxmIntel HAXMintel-power-gadgetIntel Power Gadget,b7b1b3e1dffd9b20intel-psxe-ce-c-plus-plusIntel Parallel Studio XE Composer Edition for C++,intellidockIntelliDockintellij-ideaIntelliJ IDEA Ultimate,intellij-idea-ceIntelliJ IDEA Community Edition,interarchyInterarchyinternxt-driveInternxt Driveintune-company-portalCompany PortalinvesaliusInVesaliusinvisiblixinvisibliXinvisionsyncInVision Sync,invisor-liteInvisor Lite,invokerInvokerionic-labIonicLabioquake3ioquake3ios-app-signeriOS App Signerios-consoleiOS Console,55ios-saveriOS 8 Lockscreen for OSXlatestiota-walletIOTA Walletip-in-menu-barIP in menu baripa-managerIPA Palette,ipartitioniPartitionipeIpeipepresenterIpePresenteripfsIPFS Desktopiphoto-library-manageriPhoto Library Manager,ipremoteutilityFlanders IP Remote UtilityipsecuritasIPSecuritasipvanish-vpnIPVanish,ipynb-quicklookipynb-quicklookirccloudIRCCloud DesktopireadfastiReadFastiridiumIridium BrowseririsIrisiriunwebcamIriunirpfIRPF isabelleIsabelleishowuiShowU,ishowu-instantiShowU Instant,isimulatoriSimulatorislideiSlideisolatorIsolatorbetaistat-menusiStats Menusistat-serveriStat ServeristegiStegistumbleriStumblerisubtitleiSubtitle,49iswiffiSwiff,94isynceriSyncerisyncriSyncr DesktopitauItauitchstorycall.usiterm2iTerm2ithoughtsxiThoughtsXitk-snapITK-SNAP,itoolsiToolsitrafficitrafficitsycalItsycal,itubedownloaderiTubeDownloader,itunes-produceriTunes Produceritunes-volume-controliTunes Volume ControlivideonserverIvideon ClientivolumeiVolume,ivpnIVPNizipiZipjJjabrefJabRefjadJadgjaikozJaikoz,jalbumjAlbumjalviewJalviewjameicaJameicajamesJamesjamf-migratorJamfMigratorjamiJamijamkazamJamKazamjamovijamovijamulusJamulusjandiJANDI,jandi-statusbarjandijaspJASPjasperJasperjaxx-libertyJaxx Blockchain WalletjazzupJazzUpb3,3jbidwatcherJBidwatcherpre5jbrowsejbrowsejclasslib-bytecode-viewerjclasslib bytecode viewerjcryptoolJCrypTooljd-guiJD-GUIjdiskreportJDiskReportjdk-mission-controlJDK Mission Control,07jdownloaderJDownloaderlatestjeditjEditjedit-omegaJedit Ωjellybeansoup-netflixNetflixjellyfinJellyfinjellyfin-media-playerjellyfin-media-playerjenkins-menuJenkins MenujetCodeship Jetjetbrains-spaceJetBrains Spacejetbrains-toolboxJetBrains Toolbox,jettisonJettison,jewelryboxJewelryBoxjgraspjgrasp_08jgrennison-openttdJGR's OpenTTD PatchpackjietuJietu,jigglerJigglerjiohomeJioHomejitouchjitouchlatestjitsiJitsijitsi-meetJitsi Meetjmcjmcbetajoinmestorycall.usjokerJoker iOS kernelcache handling utilitylatestjollysfastvncJollysFastVNC,joplinJoplinjoshjon-nocturnalNocturnaljosmJOSMjourneyJourneyjpadilla-rabbitmqRabbitMQbuild.1jpadilla-redisRedisbuild.1jprofilerJProfilerjqbxJQBXjsuiJSUIjtooljtoollatestjtool2jtool2jublerJublerjuliaJuliajumpJump Desktop,jumpcutJumpcutjumpshareJumpshare,jupyter-notebook-qlJupyter Notebook Quick Lookjupyter-notebook-viewerJupyter Notebook ViewerjupyterlabJupyterLab AppkactusKactuskakapoKakapokakuKakukaleidoscopeKaleidoscope,kapKapkapitainsky-rclone-browserRclone Browser,a0b66c6kapowKapowkarabiner-elementsKarabiner Elementskatalon-studioKatalon StudiokatanaKatanakatrainKaTrainkawaKawakdiff3KDiff3kdocs金山文档,keepKeepkeep-itKeep It,keepassxKeePassXkeepassxcKeePassXCkeeper-password-managerKeeper Password Manager,keepingyouawakeKeepingYouAwakekeewebKeeWebkekaKekakekaexternalhelperKeka External Helper,kernKernkext-updaterKext Updater,kext-utilityKext UtilitykextviewrKextViewrkey-codesKey Codes,keybaseKeybase,akeyboard-cleanerKeyboard Cleanerkeyboard-lockKeyboard Lockkeyboard-maestroKeyboard Maestro,keyboardcleantoolKeyboardCleanTool3keyboardholderKeyboardHolderkeycastKeyCastkeycastrKeyCastrkeycombinerkeycombiner
Источник: [storycall.us]

This is a listing of all casks available from the cask tap via the Homebrew package manager for macOS.

0-ad0 A.D.b-alphaeditor EditorbrowserBrowser1clipboard1Clipboard1password1Password1password-cli1Password CLIsafe Total Security3dgenceslicer3DGence Slicer,4k-slideshow-maker4K Slideshow Maker4k-stogram4K Stogram4k-video-downloader4K Video Downloader4k-video-to-mp34K Video to MP34k-youtube-to-mp34K YouTube to MP34peaks4Peaks5kplayer5KPlayer,8bitdo-ultimate-software8BitDo Ultimate Software8x8-meet8x8 Meet8x8-work8x8_worka-better-finder-attributesA Better Finder Attributesa-better-finder-renameA Better Finder Renamea-slower-speed-of-lightA Slower Speed of Lightableton-live-introAbleton Live Introableton-live-liteAbleton Live Liteableton-live-standardAbleton Live Standardableton-live-suiteAbleton Live SuiteabricotineabricotineabscissaAbscissaabstractAbstractabyssoft-teleportteleportaccessmenubarappsAccessMenuBarApps,15accordanceAccordance Bible SoftwareaccuricsAccurics CLIace-linkAce LinkacornAcorn,acousticbrainz-guiAcousticBrainzacquia-devAcquia Dev Desktopacronis-true-imageAcronis True ImageacslogoACSLogoactivedockActiveDock,activitywatchActivityWatchactualActualactual-odbc-packActual ODBC Driver PacklatestadapterAdapteradguardAdguardadguard-vpnAdguard VPNadiumAdiumadobe-acrobat-proAdobe Acrobat Pro DCadobe-acrobat-readerAdobe Acrobat Reader DCadobe-airAdobe AIRadobe-connectAdobe Connect11,adobe-creative-cloudAdobe Creative Cloudadobe-creative-cloud-cleaner-toolAdobe Creative Cloud Cleaner Tooladobe-digital-editionsAdobe Digital Editionsadobe-dng-converterAdobe DNG ConverteradoptopenjdkAdoptOpenJDK Java Development Kit,9adriveAliyundrivelatestadvancedrestclientAdvanced REST ClientaegisubAegisubaerialAerial ScreensaveraetherAetherdev,aexol-remote-mouseAexol Remote Mouse,5affinity-designerAffinity Designeraffinity-photoAffinity Photoaffinity-publisherAffinity Publisherafter-dark-classicAfter Dark Classic SetagendaAgenda,aimersoft-video-converter-ultimateAimersoft Video Converter Ultimateaio-creator-neoAIO CREATOR NEOair-connectAir Connect,air-video-server-hdAir Video Server HDbeta1u1,airbuddyAirBuddy,aircallAircallairdisplayAir Display,airdroidAirDroidairflowAirflowairfoilAirfoilairmediaCrestron AirMediaairparrotAirParrotairpassAirpassairqmonAirqmonairserverAirServerairtableAirtableairtameAirtameairtoolAirtool,10airtrashairtrashairunlockAirUnlockairyAiry,aja-system-testAJA System TestajourAjouralacrittyAlacrittyaladinAladin DesktopalchemyAlchemyaldenteAlDentealeo-studioAleo Studioaleph-oneAleph OnealfaviewAlfaviewalfredAlfred,algodooAlgodooalinof-timerAlinof Timeralipay-development-assistantAlipay Development AssistantaliworkbenchAliWorkBench,LqEYADnbwALXMQall-in-one-messengerAll-in-One MessengeralloyAlloyalmightyalmighty,32alt-cAlt-Caltair-graphql-clientAltair GraphQL ClientaltdeployAltDeployalternoteAlternote,altserverAltServer,59alttabAltTabalvaAlvaamadeus-proAmadeus ProamadineAmadine,amazon-chimeAmazon Chimeamazon-musicAmazon Music,_aamazon-photosAmazon Drivelatestamazon-workdocsAmazon WorkDocs,99amazon-workdocs-driveAmazon WorkDocs Drivelatestamazon-workspacesAmazon Workspacesamd-power-gadgetAMD Power GadgetamethystAmethystamitvpipPiPammAMMammoniteAmmonite,amorphousdiskmarkAmorphousDiskMark,9amppsAMPPSanacondaContinuum Analytics Anacondaananas-analytics-desktop-editionAnanas Analytics Desktop Editionandroid-commandlinetoolsAndroid SDK Command-line Toolsandroid-file-transferAndroid File Transferandroid-messagesAndroid Messages Desktopandroid-ndkAndroid NDK22bandroid-platform-toolsAndroid SDK Platform-Tools,e8b2b4cbe47candroid-sdkandroid-sdkandroid-studioAndroid StudioandroidtoolAndroidToolangbandAngbandangry-ip-scannerAngry IP Scanneranka-build-cloud-controller-and-registryAnka Build Cloud Controller & Registry,f5anka-build-cloud-registryAnka Build Cloud Registry,c83fdanka-virtualizationAnka VirtualizationankamaAnkama LauncherankiAnkiankiapp-ankiAnkiAppanonymAnonymanonymousvpnAnonymous VPNanother-redis-desktop-managerAnother Redis Desktop Manageransible-dkAnsible DK,3antconcAntConcanybarAnyBaranydeskAnyDeskanydostorycall.usanylistAnyList,2aoAoapache-couchdbApache CouchDBapache-directory-studioApache Directory StudiovM17apk-icon-editorAPK Icon Editorapp-cleanerNektony App Cleaner & Uninstaller,app-tamerAppTamer,apparencyApparency,appcleanerFreeMacSoft AppCleaner,appcodeAppCode,appdeleteAppDeleteappgate-sdp-clientAppGate SDP Client for macOSappgridAppGridappiumAppium Server Desktop GUIapple-eventsApple Eventsapple-juiceApple Juiceapplepi-bakerApplePi-BakerapppoliceAppPoliceappstore-quickviewAppStore QuickviewapptivateApptivate,15apptrapAppTrapappzapperAppZapperaptanastudioAptana StudioaptibleAptible Toolbelt,aqua-data-studioAquafold Aqua Data StudioaquamacsAquamacsaquaskkAquaSKKaquatermAquaTermaraxis-mergeAraxis MergearchipelagoArchipelagoarchiverArchiverarduinoArduinoaria-maestosaAria Maestosaaria2dAria2D,aria2guiAria2GUIariangAriaNg Nativeark-desktop-walletArk Desktop WalletarkiwiArKiwi,armoryArmoryaroundAroundarqArqarq-cloud-backupArq Cloud BackuparrsyncarRsyncart-directors-toolkitArt Directors ToolkitartisanArtisanartpipArtpipasanaAsanaasc-timetablesaSc TimeTablesascensionAscensionasciidocfxAsciidocFXasset-catalog-tinkererAsset Catalog Tinkererassinador-serproassinador-serproastah-professionalChange Vision Astah Professional,bdfastah-umlChange Vision Astah UML,bdfastro-command-centerASTRO Command CenterlatestastropadAstropad,astropad-studioAstropad Studio,atemoscatemOSCatextaText,atlantisAtlantisatlauncherATLauncheratokATOK,try3atomGithub Atomatomic-walletAtomic Walletau-labAU LabaudacityAudacityaudio-hijackAudio Hijackaudiobook-builderAudiobook Builderaudiogridder-pluginAudioGridder Pluginaudiogridder-serverAudioGridder ServeraudioscrobblerAudioscrobbleraudioslicerAudioSliceraudirvanaAudirvana,audiusAudiusaugurAugurauralAural Playeraurora-hdrAurora HDR,auryoAuryoauthyAuthy Desktopautodesk-fusionAutodesk Fusion latestautodmgAutoDMGautofirmaAutoFirmaautomuteAutoMuteautopkgrAutoPkgrautovolumeAutoVolumeautumnAutumnavast-secure-browserAvast Secure Browseravast-secureline-vpnAvast SecureLine VPNavast-securityAvast Security,avg-antivirusAVG Antivirus for Mac,aviatrix-vpn-clientAviatrix VPN Clientavibrazil-rdmRDMavidcodecsleAvid Codecs LE,3B39AE16avidemuxAvidemuxavira-antivirusAvira AntiviruslatestavitoolsAVItoolsavocodeAvocodeavogadroAvogadroavtouchbarAVTouchBar,awaAWAawareAwareawarenessAwarenessawips-pythonAWIPS Pythonlatestaws-vaultaws-vaultaws-vpn-clientAWS Client VPNaxure-rpAxure RPazirevpnAzireVPNazure-data-studioAzure Data StudiobabeleditBabelEditback-in-timeBack-In-TimebackblazeBackblazebackblaze-downloaderBackblaze Downloaderbackground-musicBackground MusicbacklogBacklogbackuploupeBackupLoupe,badlion-clientBadlion ClientbaiduinputBaidu InputlatestbaidunetdiskBaidu NetDiskbalance-lockBalance Lock,balenaetcherEtcherballastballastbalsamiq-wireframesBalsamiq WireframesbandageBandagebankidBankIDbanking-4Banking 4,banksiaguiBanksiaGuibanktivityBanktivitybansheeBansheebaretorrentbaretorrentbaritoneBaritonebarrierBarrierbartenderBartender,baseMenial Base,basecampBasecamp3basictexBasicTeXbatchmodBatChmodb5,bathyscapheBathyScaphe,batteriesBatteriesbattery-buddyBattery Buddy,11battery-reportBattery Reportbattle-netBlizzard storycall.uslatestbattlescribeBattleScribebaudlinebaudlinebbc-iplayer-downloadsBBC iPlayer DownloadsbbeditBBEditbdashBdashbdinfoBDInfobeacon-scannerBeaconScannerbeaker-browserBeaker BrowserbeamerBeamer,beanBeanbeardedspiceBeardedSpicebeatunesbeaTunesbeeBee,beekeeper-studioBeekeeper StudiobeeperBeeperbeersmithBeerSmithberrycastBerrycastbespokeBespoke SynthbestresBestRes,betaflight-configuratorBetaflight-ConfiguratorbetelgueseBetelguesebetter-window-managerBetter Window Manager,15betterdiscord-installerbetterdiscordbetterdummybetterdummybettertouchtoolBetterTouchTool,betterzipBetterZipbetweenBetweenbetwixtBetwixtbeyond-compareBeyond ComparebfxrBfxrbibdeskBibDesk,big-mean-folder-machineBig Mean Folder MachinebiglybtbiglybtbilibiliBilibilibiliminibiliminibillings-proBillings Pro,binanceBinancebinary-ninjaBinary NinjabingpaperBingPaper,46binoBinobiopassfidoBioPass FIDO2 ManagerbirdfontBirdFontbiscuitBiscuitbisqBisqbit-fiddleBit Fiddlebit-slicerBit SlicerbitbarBitBarbitcoin-coreBitcoin CorebitmessageBitmessagebitrix24Bitrix24bitsharesBitSharesbitwardenBitwardenbitwig-studioBitwig Studioblack-inkBlack Ink,blackholechBlackHole 16chblackhole-2chBlackHole 2chblackholechBlackHole 64chblenderBlenderblender-benchmarkBlender Open Data BenchmarkbleunlockBLEUnlockblheli-configuratorBLHeli Configuratorblink1controlBlink1ControlbliskBlisk BrowserblitzBlitzblobby-volley2Blobby Volley 2blobsaverblobsaverblockbenchBlockbenchblockblockBlockBlockblockstackBlockstackblocsBlocs,bloodhoundbloodhoundbloomrpcBloomRPCblu-ray-playerMacgo Mac Blu-ray Player,_blu-ray-player-proMacgo Mac Blu-ray Player Pro,_bluefishBluefishbluegriffonBlueGriffonblueharvestBlueHarvestbluejBlueJbluejeansBlueJeansbluesenseBlueSense,bluesnoozeBluesnoozebluestacksBlueStacks,cc2dbluetilityBluetilitybluewalletBlueWalletblurredBlurredbobBobboincBerkeley Open Infrastructure Flvto Youtube Downloader Latest Version License Key Archives Network Computingbome-networkBome NetworkbonitastudiocommunityBonita Studio Community Editionu0bonjeffBonjeffbonjour-browserBonjour BrowserbookendsBookendsbookmacsterBookMacsterboomBoom,boom-3dBoom 3D,boopBoopboost-notestorycall.usboostnoteBoostnotebootchampBootChampbootstrap-studioBootstrap StudiobootxchangerBootXChangerbossabossabot-framework-emulatorMicrosoft Bot Framework EmulatorbowtieBowtie,box-driveBox Drivebox-notesBox Notesbox-syncBox Syncbox-toolsBox ToolslatestboxcryptorBoxcryptorboxerBoxerboxofsnoo-fairmountFairmountboxy-suiteBoxy SuitelatestbracketsBracketsbrain-workshopBrain Workshopbrainfmstorycall.usbrave-browserBrave,breaktimerBreakTimerbreitbandmessungBreitbandmessungbrewletBrewletuniversalbrewservicesmenubarBrew Services MenubarbrewtargetbrewtargetbriaBria,bricklink-partdesignerPartDesigner_5bricklink-studioStudio_1bricksmithBricksmithbrightnessBrightnessbrightness-syncBrightness SyncbriskBriskbrisyncBrisyncbrl-cad-mgedBRL-CADbrookBrookbrooklynBrooklynbrowserosaurusBrowserosaurusbrowserstacklocalBrowserStack Local Testingbtcpayserver-vaultBTCPayServer VaultbuboBubobucketsBucketsbugdomBugdombuildsettingextractorBuildSettingExtractorbunchBunch,bunqcommunity-bunqbunqDesktopburnBurnburp-suiteBurp Suite Community Editionburp-suite-professionalBurp Suite ProfessionalbusycalBusyCal,busycontactsBusyContacts,butlerButler,buttBroadcast Using This ToolbutterButterbuttercupButtercupbwanaBwanabzflagBZFlagc0reqbittorrentqBittorrent Enhanced EditioncabalCabalcacherCachercaffeineCaffeinecajviewerCAJViewer,10cakebrewCakebrewcakebrewjscakebrewjscalcserviceCalcServicecalendarCalendar II,calibrecalibrecalmly-writerCalmly WritercamedCAM Editorcamera-liveCamera Live11camerabag-photoCameraBagcamo-studioCamo Studio,camtasiaCamtasiacamunda-modelerCamunda ModelercandybarCandyBarcantataCantatacanvaCanvacaprineCaprinecaptainCaptaincaptinCaptin,captionCaptioncaptoCapto,carbon-copy-clonerCarbon Copy ClonercardhopCardhop,caretCaretcashnotifyCashNotifycastrcastrcatchCatchcatlightcatlightcave-storyPixel Cave Story,2ccleanerPiriform CCleanerccmenuCCMenucctalkCCtalkcd-tocd tocelestiaCelestiacelestialteapot-runwayRunway,celldesignerCellDesignercellprofilerCellProfilercemuCEmucerebroCerebrocernboxCERNBox ClientcevelopCevelopchaiChaichalkChalkchameleon-ssd-optimizerChameleon SSD optimizergcharlesCharlescharlessoft-timetrackerTimeTrackerchatmate-for-facebookChatMate for Facebook,chatmate-for-whatsappChatMate for WhatsApp,chatologyChatologychatterinoChatterinochattyChattychatworkChatWorkcheatsheetCheatSheetcheckra1ncheckra1ncheetah3dCheetah3Dchef-workstationChef WorkstationchemdoodleChemDoodlechessxChessXchiaChia BlockchainchiakiChiakichirpCHIRPchocolatChocolatchoosyChoosychrome-devtoolsChrome DevToolschrome-remote-desktop-hostChrome Remote DesktopchromedriverChromeDriverchromiumChromiumchronicleChronicle,chronoagentChronoAgentchronosChronos TimetrackerchronosyncChronoSyncchronycontrolChronyControl,chrysalisChrysaliscinc-workstationCinc WorkstationcinchCinch,cincoCincocinderCindercinderellaCinderellabcinebenchCinebenchR23,circuitjs1Falstad CircuitJScirrusCirrus,cisco-jabberCisco Jabbercisco-proximityCisco Proximitydesktopcisdem-data-recoveryCisdem Data Recoverycisdem-document-readerCisdem Document Readercisdem-pdf-converter-ocrCisdem PDF Converter OCRcisdem-pdfmanagerultimateCisdem PDFManagerUltimatecitraCitralatestcityofzion-neonNeon WalletckanComprehensive Kerbal Archive Networkckb-nextckb-nextclamxavClamXAV,clash-for-windowsClash for WindowsclashxClashXclassicftpClassicFTPclassroom-assistantGitHub Classroom Assistantclassroom-mode-for-minecraftClassroom Mode for Minecraftclayclayclean-meClean-mecleanappSynium Software CleanAppcleanmymacCleanMyMac X,cleanshotCleanShotcleartextCleartextclementineClementineclickchartsClickChartsclicker-for-netflixClicker for Netflixclicker-for-youtubeClicker for YouTube,52clickupClickUpclionCLion,clip-studio-paintClip Studio PaintclipgrabClipGrabclipyClipyclixCLIXcljstylecljstyleclockClockclock-barClock Bar,clock-signalClock SignalclockerClockerclockifyClockify,clocksaverstorycall.us screensaverclone-heroClone HeroclonkClonk Ragecloud-pbxCloud PBXcloudappCloudApp,cloudashcloudashcloudcompareCloudComparelatestcloudflare-warpCloudflare WARP,cloudmounterEltima CloudMounter,cloudupCloudupcloudytabsCloudyTabsclover-configuratorClover ConfiguratorcmakeCMakecmd-eikanacmd-eikanacmdtapCmdTapcncjsCNSjscncnetCnCNet: Classic Command & ConquercoarchicoArchi plugin for ArchicoccinellidaCoccinellidacoccocCốc Cốc,cockatriceCockatrice,PrismcocktailCocktailcocoapodsstorycall.uscocoarestclientCocoaRestClientcocoaspellcocoAspellcoconutbatterycoconutBattery,cbcoconutidcoconutIDcodaPanic Coda,code-composer-studioCode Composer Studio (CCS)code-notesCode NotescodecrashplanCode42 CrashPlan,codeexpanderCodeExpandercodekitCodeKit,codeliteCodeLitecodeqlCodeQLcoderunnerCodeRunner,codespaceCodespacecoffitivity-offlineCoffitivity OfflinecogCog,cb8coin-walletCoin Walletcoinomi-walletCoinomi Walletcold-turkey-blockerCold Turkeycolor-oracleColor Oraclecolorchecker-camera-calibrationColorChecker Camera Calibrationcolorpicker-developerDeveloper Color Pickercolorpicker-materialdesignMaterial Designcolorpicker-propickerPro Pickercolorpicker-skalacolorSkala ColorcolorsnapperColorSnapper 2colortesterColorTestercolorwellColorWellcolour-contrast-analyserColour Contrast Analyser (CCA)combine-pdfsCombine PDFscomictaggerComicTaggercomma-chameleonComma Chameleoncommand-padCommand Padcommand-tab-plusCommand-Tab Plus,commander-oneCommander One,commandqCommandQcomposercatComposercatcompositorCompositorconferencesstorycall.uslalpha22connectiqGarmin Connect IQ SDK,af9bconnectmenowConnectMeNowconsoleConsolecontainer-psContainer PScontextsContexts,continuity-activation-toolContinuity Activation ToolcontrasteContraste,controllermateControllerMatecontrolplaneControlPlaneconvert3dguiConvert3DGUIcookieCookiecool-retro-termcool-retro-termcooltermCoolTermcopyclipCopyClipcopyqCopyQcopytranslatorCopyTranslatorcoqideCoqcordCoRD,core-data-editorCore Data EditorcorelocationcliCore Location CLIcornercalCornerCalcornerstoneCornerstonecorona-trackerCorona TrackercorrettoAWS Corretto JDKcoscreenCoScreencoteditorCotEditorcouchbase-server-communityCouchbase Servercouchbase-server-enterpriseCouchbase ServercouchpotatoCouchPotatocouleursCouleurs,countdownCountdown ScreensavercoverloadCoverLoadcozy-driveCozy DrivecpuinfocpuinfocrCool Reader,10craftmanagerCraftManager,create-recovery-partition-installerCreate Recovery Partition InstallercreateuserpkgCreateUserPkgcreepyCreepycrescendoCrescendocriptextCriptext,cronnixCronniXcrossoverCrossOvercrosspack-avrCrossPackcrunchCrunchcrushftpCrushFTP10cryocryocrypterCryptercryptomatorCryptomatorcryptonomic-galleonGalleonbcryptrCryptrcrystalmakerCrystalMakercrystax-ndkCrystax NDKcscreencscreencubicsdrCubicSDRcuda-zCUDA-ZcumulusCumuluscura-lulzbotCura LulzBot Edition,ce3e47accurioCurio15,curiosityCuriositycurseforgeCurseForgecursorcererCursorcererlatestcursorsenseCursorSensecustomshortcutsCustomShortcuts,cutesdrCuteSDRcutterCuttercyberduckCyberduck,cyberghost-vpnCyberGhost,cyclingmaxCycling ‘74 Max_daedalus-mainnetDaedalus Mainnet,daedalus-testnetDaedalus Testnet,daisydiskDaisyDiskdangerzoneDangerzonedarktabledarktabledarwindumperDarwinDumper,dashDash,dash-dashDashdashcam-viewerDashcam ViewerdashlaneDashlanedatDat Desktopdata-integrationPentaho Data 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Источник: [storycall.us]

An Overview of Cryptography

1. INTRODUCTION

Does increased security provide comfort to paranoid people? Or does security provide some very basic protections that we are naive to believe that we don't need? During this time when the Internet provides essential communication between literally billions of people and is used as a tool for commerce, social interaction, and the exchange of an increasing amount of personal information, security has become a tremendously important issue for every user to deal with.

There are many aspects to security and many applications, ranging from secure commerce and payments to private communications and protecting health care F-Secure VPN Plus Client v5.0 crack serial keygen. One essential aspect for secure communications is that of cryptography. But it is important to note that while cryptography is necessary for secure communications, it is not by itself sufficient, F-Secure VPN Plus Client v5.0 crack serial keygen. The reader is advised, then, that the topics covered here only describe the first of many steps necessary for better security in any number of situations.

This paper has two major purposes. The first is to define some of the terms and concepts behind basic cryptographic methods, and to offer a way to compare the myriad cryptographic schemes in use today. The second is to provide some real examples of cryptography in use today. (See Section A.4 for some additional commentary on this)

DISCLAIMER: Several companies, products, and services are mentioned in this tutorial. Such mention is for example purposes only and, unless explicitly stated otherwise, should not be taken as a recommendation or endorsement by the author.

2. BASIC CONCEPTS OF CRYPTOGRAPHY

Cryptography &#; the science of secret writing &#; is an ancient art; the first documented use of cryptography in writing dates back to circa B.C. when an Egyptian scribe used non-standard hieroglyphs in an inscription. Some experts argue that cryptography appeared spontaneously sometime after writing was invented, with applications ranging from diplomatic missives to war-time battle plans. It is no surprise, then, that new forms of cryptography came soon after the widespread development of computer communications. In data and telecommunications, cryptography is necessary when communicating over any untrusted medium, which includes just about any network, particularly the Internet.

There are five primary functions of cryptography:

  1. Privacy/confidentiality: Ensuring that no one can read the message except the PhpStorm 2021.2.1 Crack With Activation Code [Latest 2021] receiver.
  2. Authentication: The process of proving one's identity.
  3. Integrity: Assuring the receiver that the received message has not been altered in any way from the original.
  4. Non-repudiation: A mechanism to prove that the sender really sent this message.
  5. Key exchange: The method by which crypto keys are shared between sender and receiver.

In cryptography, we start with the unencrypted data, referred to as plaintext. Plaintext is encrypted into ciphertext, which will in turn (usually) be decrypted back into usable plaintext. The encryption and decryption is based upon the type of cryptography scheme being employed and some form of key. For those who like formulas, this process is sometimes written as:

C = Ek(P)
P = Dk(C)

      where P = plaintext, C = ciphertext, E = the encryption method, D = the decryption method, and k = the key.

Given this, there are other functions that might be supported by crypto and other terms that one might hear:

  • Forward Secrecy (aka Perfect Forward Secrecy): This feature protects past encrypted sessions from compromise even if the server holding the messages is compromised. This is accomplished by creating a different key for every session so that compromise of a single key does not threaten the entirely of the communications.
  • Perfect Security: A system that is unbreakable and where the ciphertext conveys no information about the plaintext or the key. To achieve perfect security, the key has to be at least as long as the plaintext, making analysis and even brute-force attacks impossible. One-time pads are F-Secure VPN Plus Client v5.0 crack serial keygen example of such a system.
  • Deniable Authentication (aka Message Repudiation): A method whereby participants in an exchange of messages can be assured in the authenticity of the messages but in such a way that senders can later plausibly deny their participation to a third-party.

In many of the descriptions below, two communicating parties will be referred to as Alice and Bob; this is the common nomenclature in the crypto field and literature to make it easier to identify the communicating parties. If there is a third and fourth party to the communication, F-Secure VPN Plus Client v5.0 crack serial keygen, they will be referred to as Carol and Dave, respectively. A malicious party is referred to as Mallory, an eavesdropper as Eve, and a trusted third party as Trent.

Finally, cryptography is most closely associated with the development and creation of the mathematical algorithms used to encrypt and decrypt messages, whereas cryptanalysis is the science of analyzing and breaking encryption schemes. Cryptology is the umbrella term referring to the broad study of secret writing, and encompasses both cryptography and cryptanalysis.

3. TYPES OF CRYPTOGRAPHIC ALGORITHMS

There are several ways of classifying cryptographic algorithms. For purposes of this paper, they will be categorized based on the number of keys that are employed for encryption and decryption, and further defined by their application and use. The three types of algorithms that will be discussed are (Figure 1):

  • Secret Key Cryptography (SKC): Uses a single key for both encryption and decryption; also called symmetric encryption. Primarily used for F-Secure VPN Plus Client v5.0 crack serial keygen and confidentiality.
  • Public Key Cryptography (PKC): Uses one key for encryption and another for decryption; also called asymmetric encryption. Primarily used for authentication, non-repudiation, and key exchange.
  • Hash Functions: Uses a mathematical transformation to irreversibly "encrypt" information, providing a digital fingerprint. Primarily used for message integrity.

FIGURE 1: Three types of cryptography: secret key, public key, and hash function.

Secret Key Cryptography

Secret key cryptography methods employ a single key for both encryption and decryption. As shown in Figure 1A, the sender uses the key to encrypt the plaintext and sends the ciphertext to the receiver. The receiver applies the same key to decrypt the message and recover the plaintext. Because a single key is used for both functions, secret key cryptography is also called symmetric enfocus pitstop pro 2020 Archives With this form of cryptography, it is obvious that the key must be known to both the sender and the receiver; that, in fact, is the secret. The biggest difficulty with this approach, of course, is the distribution of the key (more on that later in the discussion of public key cryptography).

Secret key cryptography schemes are generally categorized as being either stream ciphers or block ciphers.

A) Self-synchronizing stream cipher. (From Schneier,Figure )

B) Synchronous stream cipher. (From Schneier,Figure )

FIGURE 2: Types of stream ciphers.

Stream ciphers operate on a single bit (byte or computer word) at a time and implement some form of feedback mechanism so that the key is constantly changing. Stream ciphers come in several flavors but two are worth mentioning here (Figure 2). Self-synchronizing stream ciphers calculate each bit in the keystream as a function of the previous n bits in the keystream. It is F-Secure VPN Plus Client v5.0 crack serial keygen "self-synchronizing" because the decryption process can stay synchronized with the encryption process merely by knowing how far into the n-bit keystream it is. One problem is error propagation; a garbled bit in transmission will result in n garbled bits at the receiving side. Synchronous stream ciphers generate the F-Secure VPN Plus Client v5.0 crack serial keygen in a fashion independent of the message stream but by using the same keystream generation function at sender and receiver. While stream ciphers do not propagate transmission errors, they are, by their nature, periodic so that the keystream will eventually repeat.

FIGURE 3: Feistel cipher. (Source: Wikimedia Commons)

A block cipher is so-called because the scheme encrypts one fixed-size block of data at a time. In a block cipher, a given plaintext block will always encrypt to the F-Secure VPN Plus Client v5.0 crack serial keygen ciphertext when using the same key (i.e., it is deterministic) whereas the same plaintext will encrypt to different ciphertext in a stream cipher. The most common construct for block encryption algorithms is the Feistel cipher, named for cryptographer Horst Feistel (IBM). As shown in Figure 3, a Feistel cipher combines elements of substitution, permutation (transposition), and key expansion; these features create a large amount of "confusion and diffusion" (per Claude Shannon) in the cipher. One advantage of the Feistel design is that the encryption and decryption stages are similar, sometimes identical, requiring only a reversal of the key operation, thus dramatically reducing the size of the code or circuitry necessary to implement the cipher in software or hardware, respectively. One of Feistel's early papers describing this operation is "Cryptography and Computer Privacy" (Scientific American, MayF-Secure VPN Plus Client v5.0 crack serial keygen, (5), ).

Block ciphers can operate in one of several modes; the following are the most important:

  • Electronic Codebook (ECB) mode is the simplest, most obvious application: the secret key is used to encrypt the plaintext block to form a ciphertext block. Two identical plaintext blocks, then, will always generate the same ciphertext block. ECB is susceptible to a variety of brute-force attacks (because of the fact that the same plaintext block will always encrypt to the same ciphertext), as well as deletion and insertion attacks. In addition, a single bit error in the transmission of the ciphertext results in an error in the entire block of decrypted plaintext.
  • Cipher Block Chaining (CBC) mode adds a feedback mechanism to the encryption scheme; the plaintext is exclusively-ORed (XORed) with the previous ciphertext block prior to encryption so that two identical plaintext blocks will encrypt differently. While CBC protects against many brute-force, F-Secure VPN Plus Client v5.0 crack serial keygen, deletion, and insertion attacks, a single bit error in the ciphertext yields an entire block error in the decrypted plaintext block and a bit error in the next decrypted plaintext block.
  • Cipher Feedback (CFB) mode is a block cipher implementation as a self-synchronizing stream cipher. CFB mode allows data to be encrypted in units smaller than the block size, which might be useful in some applications such as encrypting interactive terminal input. If we were using one-byte CFB mode, for example, each incoming character is placed into a shift register the same size as the block, encrypted, and the block transmitted. At the receiving side, the ciphertext is decrypted and the extra bits in the block (i.e., everything above and beyond the one byte) are discarded. CFB mode generates a keystream based upon the previous ciphertext (the initial key comes from an Initialization Vector [IV]). In this mode, a single bit error in the ciphertext affects both this block and the following one.
  • Output Feedback (OFB) mode is a block cipher implementation conceptually similar to a synchronous stream cipher. OFB prevents the same plaintext block from generating the same ciphertext block by using an internal feedback mechanism that generates the keystream independently of both the plaintext and ciphertext bitstreams. In OFB, a single bit error in ciphertext yields a single bit error in the decrypted plaintext.
  • Counter (CTR) mode is a relatively modern addition to block ciphers. Like CFB and OFB, CTR mode operates on the blocks as in a stream cipher; like ECB, CTR mode operates on the blocks independently. Unlike ECB, however, CTR uses different key inputs to different blocks so that two identical blocks of plaintext will not result in the same ciphertext. Finally, each block of ciphertext has specific location within the encrypted message. CTR mode, then, allows blocks to be processed in parallel &#; thus offering performance advantages when parallel processing and multiple processors are available &#; but is not susceptible to ECB's brute-force, deletion, and insertion attacks.

A good overview of these different modes can be found at CRYPTO-IT.

Secret key cryptography algorithms in use today &#; or, at least, important today even if not in use &#; include:

  • Data Encryption Standard (DES): One of the most well-known and well-studied SKC schemes, DES was designed by IBM in the s and adopted by the National Bureau of Standards (NBS) [now the National Institute of Standards and Technology (NIST)] in for commercial and unclassified government applications. DES is a Feistel block-cipher employing a bit key that operates on bit blocks. DES has a complex set of rules and transformations that were designed specifically to yield fast hardware implementations and slow software implementations, although this latter point is not significant today since the speed of computer processors is several orders of magnitude faster today than even twenty years ago. DES was based somewhat on an earlier cipher from Feistel called Lucifer which, some sources report, had a bit key. This was rejected, partially in order to fit the algorithm onto a single chip and partially because of the National Security Agency (NSA). The NSA also proposed a number of tweaks to DES that many thought were introduced in order to weaken the cipher; analysis in the s, however, showed that the NSA suggestions actually strengthened DES, F-Secure VPN Plus Client v5.0 crack serial keygen, including the removal of a mathematical back door by a change to the design of the S-box (see "The Legacy of DES" by Bruce Schneier []). In Aprilthe NSA declassified a fascinating historical paper titled "NSA Comes Out of the Closet: The Debate over Public Cryptography in the Inman Era" that appeared in Cryptologic Quarterly, Spring

    DES was defined in American National Standard X and three Federal Information Processing Standards (FIPS), all withdrawn in

    • FIPS PUB DES (Archived file)
    • FIPS PUB Guidelines for Implementing and Using the NBS Data Encryption Standard
    • FIPS PUB DES Modes of Operation

    Information about vulnerabilities of DES can be obtained from the Electronic Frontier Foundation.

    Two important variants that strengthen DES are:

    • Triple-DES (3DES): A variant of DES that employs up to three bit keys and makes three encryption/decryption passes over the block; 3DES is also described in FIPS PUB and was an interim replacement to DES in the lates and earlys.

    • DESX: A variant devised by Ron Rivest. By combining 64 additional key bits to the plaintext prior to encryption, effectively increases the keylength to bits.

    More detail about DES, 3DES, and DESX can be found below in Section

  • Advanced Encryption Standard (AES): InNIST initiated a very public, /2 year process to develop a new secure cryptosystem for U.S. government applications (as opposed to the very closed process in the adoption of DES 25 years earlier). The result, the Advanced Encryption Standard, became the official successor to DES in December AES uses an SKC scheme called Rijndael, a block cipher designed by Belgian cryptographers Joan Daemen and Vincent Rijmen. The algorithm can use a variable block length and key length; the latest specification allowed any combination of keys lengths of, or bits and blocks of length, or bits. NIST initially selected Rijndael in October and formal adoption as the AES standard came in December FIPS PUB describes a bit block cipher employing a, or bit key. AES is also part of the NESSIE approved suite of protocols. (See also the entries for CRYPTEC and NESSIE Projects in Table 3.)

    The AES process and Rijndael algorithm are described F-Secure VPN Plus Client v5.0 crack serial keygen more detail below in Section

  • CAST/ CAST (aka CAST5), described in Request for Comments (RFC)is a DES-like substitution-permutation crypto algorithm, employing a bit key operating on a bit block. CAST (aka CAST6), described in RFCis an extension of CAST, using a bit block size and a variable length (, F-Secure VPN Plus Client v5.0 crack serial keygen,or bit) key. CAST is named for its developers, Carlisle Adams and Stafford Tavares, and is available internationally. CAST was one of the Round 1 algorithms in the AES process.

  • International Data Encryption Algorithm (IDEA): Secret-key cryptosystem written by Xuejia Lai and James Massey, in and patented by Ascom; a bit SKC block cipher using a bit key.

  • Rivest Ciphers (aka Ron's Code): Named for Ron Rivest, a series of SKC algorithms.

    • RC1: Designed on paper but never implemented.

    • RC2: A bit block cipher using variable-sized keys designed to replace DES. It's code has not been made public although many companies have licensed RC2 for use in their products. Described in RFC

    • RC3: Found to be breakable during development.

    • RC4: A stream cipher using variable-sized keys; it is widely used in commercial cryptography products. An update to RC4, called Spritz (see also this article), was designed by Rivest and Jacob Schuldt. More detail about RC4 (and a little about Spritz) can be found below in Section

    • RC5: A block-cipher supporting a variety of block sizes (32, 64, or bits), key sizes, and number of encryption passes over the data. Described in RFC

    • RC6: A bit block cipher based upon, and an improvement over, RC5; RC6 was one of the AES Round 2 algorithms.

  • Blowfish: A symmetric bit block cipher invented by Bruce Schneier; optimized for bit processors with large data caches, it is significantly faster than DES on a Pentium/PowerPC-class machine. Key lengths can vary from 32 to bits in length. Blowfish, available freely and intended as a substitute for DES or IDEA, is in use in a large number of products.

  • Twofish: A bit block cipher using, or bit keys. Designed to be highly secure and highly flexible, well-suited for large microprocessors, 8-bit smart card microprocessors, and dedicated hardware. Designed by a team led by Bruce Schneier and was one of the Round 2 algorithms in the AES process.

  • Threefish: A large block cipher, supporting, and bit blocks and a key size that matches the block size; by design, the block/key size can grow in increments of bits. Threefish only uses XOR operations, addition, and rotations of bit words; the design philosophy is that F-Secure VPN Plus Client v5.0 crack serial keygen algorithm employing many computationally simple rounds is more secure than one employing highly complex &#; albeit fewer &#; rounds. The specification for Threefish is part of the Skein Hash Function Family documentation.

  • Anubis: Anubis is a block cipher, co-designed by Vincent Rijmen who was one of the designers of Rijndael. Anubis is a block cipher, performing substitution-permutation operations on bit blocks and employing keys of length to bits (in bit increments). Anubis works very much like Rijndael. Although submitted to the NESSIE project, it did not make the final cut for inclusion.

  • ARIA: A bit block cipher employingMikroTik License Generator Archives, and bit keys to encrypt bit blocks in 12, 14, and 16 rounds, depending on the key size. Developed by large group of researchers from academic institutions, research institutes, and federal agencies in South Korea inand subsequently named a national standard. Described in RFC

  • Camellia: A secret-key, F-Secure VPN Plus Client v5.0 crack serial keygen, block-cipher crypto algorithm developed jointly by Nippon Telegraph and Telephone (NTT) Corp. and Mitsubishi Electric Corporation (MEC) in Camellia has some characteristics in common with AES: a bit block size, support for, and bit key lengths, and suitability for both software F-Secure VPN Plus Client v5.0 crack serial keygen hardware implementations on common bit processors as well as 8-bit processors (e.g., smart cards, cryptographic hardware, and embedded systems). Also described in RFC Camellia's application in IPsec is described in RFC and application in OpenPGP in RFC Camellia is part of the NESSIE suite of protocols.

  • CLEFIA: Described in RFCCLEFIA is a bit block cipher employing key lengths of, and bits (which is compatible with AES). The CLEFIA algorithm was first published in by Sony Corporation. CLEFIA is one of the new-generation lightweight blockcipher algorithms designed after AES, offering high performance in software and hardware as well as a lightweight implementation in hardware.

  • FFX-A2 and FFX-A10: FFX (Format-preserving, Feistel-based encryption) is a type of Format Preserving Encryption (FPE) scheme that is designed so that the ciphertext has the same format as the plaintext. FPE schemes are used for such purposes as encrypting social security numbers, credit card numbers, limited size protocol traffic, etc.; this means that an encrypted social security number, for example, would still be a nine-digit string. FFX can theoretically encrypt strings of arbitrary length, although it is intended for message sizes smaller than that of AES (2 points). The FFX version specification describes FFX-A2 and FFX-A10, which are intended for bit binary strings or digit decimal strings.

  • GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile) encryption: GSM mobile phone systems use several stream ciphers for over-the-air communication privacy. A5/1 was developed in for use in Europe and the U.S. A5/2, developed inis a weaker algorithm and intended for use outside of Europe and the U.S. Significant flaws were found in both ciphers after the "secret" specifications were leaked inhowever, and A5/2 has been withdrawn from use. The newest version, A5/3, employs the KASUMI block cipher. NOTE: Unfortunately, although A5/1 has been repeatedly "broken" (e.g., see "Secret code protecting cellphone calls set loose" [] and "Cellphone snooping now easier and cheaper than ever" []), F-Secure VPN Plus Client v5.0 crack serial keygen, this encryption scheme remains in widespread use, even in 3G and 4G mobile phone networks. Use of this scheme is reportedly one of the reasons that the National Security Agency (NSA) can easily decode voice and data calls over mobile phone networks.

  • GPRS (General Packet Radio Service) encryption: GSM mobile phone systems use GPRS for data applications, and GPRS uses a number of encryption methods, F-Secure VPN Plus Client v5.0 crack serial keygen, offering different levels of data protection. GEA/0 offers no encryption at all. GEA/1 and GEA/2 WinRAR 6.02 Crack 2021 proprietary stream ciphers, employing a bit transmac how to use Archives and a bit or bit state, respectively, F-Secure VPN Plus Client v5.0 crack serial keygen. GEA/1 and GEA/2 are most widely used by network service providers today although both have been reportedly broken. GEA/3 is a bit block cipher employing a bit key that is used by some carriers; GEA/4 is a bit clock cipher with a bit key, but is not yet deployed.

  • KASUMI: A block cipher using a bit key that is part of the Third-Generation Partnership Project (3gpp), formerly known as the Universal Mobile Telecommunications System (UMTS). KASUMI is the intended confidentiality and integrity algorithm for both message content and signaling data for emerging mobile communications systems.

  • KCipher Described in RFCKCipher-2 is a stream cipher with a bit key and a bit initialization vector. Using simple arithmetic operations, the algorithms offers fast encryption and decryption by use of efficient implementations. KCipher-2 has been used for industrial applications, especially for mobile health monitoring and diagnostic services in Japan.

  • KHAZAD:KHAZAD is a so-called legacy block cipher, operating on bit blocks à la older block ciphers such as DES and IDEA. KHAZAD uses eight rounds of substitution and permutation, with a bit key.

  • KLEIN: Designed inKLEIN is a lightweight, bit block cipher supportingand bit keys. KLEIN is designed for highly resource constrained devices such as wireless sensors and RFID tags.

  • Light Encryption Device (LED): Designed inLED is a lightweight, bit block cipher supporting and bit keys. LED is designed for RFID tags, sensor networks, and other applications with devices constrained by memory or compute power.

  • MARS:MARS is a block cipher developed by IBM and was one of the five finalists in the AES development F-Secure VPN Plus Client v5.0 crack serial keygen. MARS employs bit blocks and a variable key length from to bits. The MARS document stresses the ability of the algorithm's design for high speed, high security, and the ability to efficiently and effectively implement the scheme on a wide range of computing devices.

  • MISTY1: Developed at Mitsubishi Electric Corp., a block cipher using a bit key and bit blocks, and a variable number of rounds. Designed for hardware and software implementations, and is resistant to differential and linear cryptanalysis. Described in RFCMISTY1 is part of the NESSIE suite.

  • Salsa and ChaCha: Salsa20 is a stream cipher proposed for the eSTREAM project by Daniel Bernstein. Salsa20 uses a pseudorandom function Jogos de Precision Platformer de Graça para Baixar on bit (whole word) addition, bitwise addition (XOR), and rotation operations, aka add-rotate-xor (ARX) operations. Salsa20 uses a bit key although a bit key variant also exists. InBernstein published ChaCha, a new family of ciphers related to Salsa ChaCha20, originally defined in RFC (now obsoleted), is employed (with the Poly authenticator) in Internet Engineering Task Force (IETF) protocols, most notably for IPsec and Internet Key Exchange (IKE), per RFCand Transaction Layer Security (TLS), per RFC InGoogle adopted ChaCha20/Poly for use in OpenSSL, and they are also a part of OpenSSH. RFC replaces RFCand provides an implementation guide for both the ChaCha20 cipher and Poly message authentication code, as well as the combined CHACHAPOLY Authenticated-Encryption with Associated-Data (AEAD) algorithm.

  • Secure and Fast Encryption Routine (SAFER): A series of block ciphers designed by James Massey for implementation in software and employing a bit block. SAFER K, published inused a bit key and SAFER K, published inemployed a bit key. After weaknesses were found, new versions were released called SAFER SK, SK, and SK, using, and bit keys, respectively. SAFER+ () used a bit block and was an unsuccessful candidate for the AES project; SAFER++ () was submitted to the NESSIE project.

  • SEED: A block cipher using bit blocks and bit keys. Developed by the Korea Information Security Agency (KISA) and adopted as a national standard encryption algorithm in South Korea. Also described in RFC

  • Serpent:Serpent is another of the AES finalist algorithms. Serpent supports, or bit keys and a block size of F-Secure VPN Plus Client v5.0 crack serial keygen, and is a round substitution–permutation network operating on a block of four bit words. The Serpent developers opted for a high security margin in the design of the algorithm; they determined that 16 rounds would be sufficient against known attacks but require 32 rounds in an attempt to future-proof the algorithm.

  • SHACAL: SHACAL is a pair of block ciphers based upon the Secure Hash Algorithm (SHA) and the fact that SHA is, at heart, a compression algorithm. As a hash function, SHA repeatedly calls on a compression scheme to alter the state of the data blocks. While SHA (like other hash functions) is irreversible, the compression function can be used for encryption by maintaining appropriate state information, F-Secure VPN Plus Client v5.0 crack serial keygen. SHACAL-1 is based upon SHA-1 and uses a bit block size while SHACAL-2 is based upon SHA and employs a bit block size; both support key sizes from to bits. SHACAL-2 is one of the NESSIE block ciphers.

  • Simon and Speck: Simon and Speck are a pair of lightweight block ciphers proposed by the NSA indesigned for highly constrained software or hardware environments. (E.g., per the specification, AES requires gate equivalents and these ciphers require less than ) While both cipher families perform well in both hardware and software, Simon has been optimized for high performance on hardware devices and Speck for performance in software. Both are Feistel ciphers and support ten combinations of block and key size:

  • Skipjack: SKC scheme proposed, along with the Clipper chip, F-Secure VPN Plus Client v5.0 crack serial keygen, as part of the never-implemented Capstone project. Although the details of the algorithm were never made public, Skipjack was a block cipher using an bit key and 32 iteration cycles per bit block. Capstone, proposed by NIST and the NSA as a standard for public and government use, met with great resistance by the crypto community largely because the design of Skipjack was classified (coupled with the key escrow requirement of the Clipper chip).

  • SM4: Formerly called SMS4, SM4 is a bit block cipher using bit keys and 32 rounds to process a block. Declassified inSM4 is used in the Chinese National Standard for Wireless Local Area Network (LAN) Authentication and Privacy Infrastructure (WAPI). SM4 had been a proposed cipher for the Institute of Electrical and Electronics Engineers (IEEE) i standard on security mechanisms for wireless LANs, but has yet to be accepted by the IEEE or International Organization for F-Secure VPN Plus Client v5.0 crack serial keygen (ISO). SM4 is described in SMS4 Encryption Algorithm for Wireless Networks (translated by Whitfield Diffie and George Ledin, ) and at the SM4 (cipher) page. SM4 is issued by the Chinese State Cryptographic Authority as GM/T SM4 ().

  • Tiny Encryption Algorithm (TEA): A family of block ciphers developed by Roger Needham and David Wheeler. TEA was originally developed inand employed a bit key, bit block, and 64 rounds of operation. To correct certain weaknesses in TEA, eXtended TEA (XTEA), aka Block TEA, was released in To correct weaknesses in XTEA and add versatility, Corrected Block TEA (XXTEA) was published in XXTEA also uses a bit key, but block size can be any multiple of bit words (with a minimum block size of 64 bits, or two words) and the number of rounds is a function of the block size (~52+6*words), F-Secure VPN Plus Client v5.0 crack serial keygen shown in Table 1.

  • Block Size
    2n
    Key Size
    mn
    Word Size
    n
    Key Words
    m
    Rounds
    T
    326416432
    4872
    96
    243
    4
    36
    36
    6496
    323
    4
    42
    44
    9696
    482
    3
    52
    54


    642
    3
    4
    68
    69
    72
  • TWINE: Designed by engineers at NEC inTWINE is a lightweight, bit block cipher supporting and bit keys. TWINE's design goals included maintaining a small footprint in a hardware implementation (i.e., fewer than 2, gate equivalents) and small memory consumption in a software implementation.

Although not an SKC scheme, check out Section about Shamir's Secret Sharing (SSS).

There are several other references that describe interesting algorithms and even SKC codes dating back decades. Two that leap to mind are the Crypto Museum's Crypto List and John J.G. Savard's (albeit old) A Cryptographic Compendium page.

Public Key Cryptography

Public key cryptography has been said to be the most significant new development in cryptography in the last years. Modern PKC was first described publicly by Stanford University professor Martin Hellman and graduate student Whitfield Diffie in Their paper described a two-key xlstat crack free download Archives system in which two parties could engage in a secure communication over a non-secure communications channel without having to share a secret key.

PKC depends upon the existence of so-called one-way functions, or mathematical functions that are easy to compute whereas Adobe After Effects Beta v3.1 crack serial keygen inverse function is relatively difficult to compute. Let me give you two simple examples:

  1. Multiplication vs, F-Secure VPN Plus Client v5.0 crack serial keygen. factorization: Suppose you have two prime numbers, 3 and 7, and you need to calculate the product; it should take almost no time to calculate that value, which is Now suppose, instead, that you have a number that is a product of two primes, 21, and you need to determine those prime factors. You will eventually come up with the solution but whereas calculating the product took milliseconds, factoring will take longer. The problem becomes much harder if we start with primes that have, say, digits or so, because the product will have ~ digits.
  2. Exponentiation vs. logarithms: Suppose you take the number 3 to the 6th power; again, it is relatively easy to calculate 36 =  But if you start with the number and need to determine the two integers, x and y so that logx  = y, it will take longer to find the two values.

While the examples above are trivial, they do represent two of the functional pairs that are used with PKC; namely, the ease of multiplication and exponentiation versus the relative difficulty of factoring and calculating logarithms, respectively. The mathematical "trick" in PKC is to find a trap door in the one-way function so that the inverse calculation becomes easy given knowledge of some item of F-Secure VPN Plus Client v5.0 crack serial keygen Generic PKC employs two keys that are mathematically related although knowledge of one key does not allow someone to easily determine the other key, F-Secure VPN Plus Client v5.0 crack serial keygen. One key is used to encrypt the plaintext and the other key is used to decrypt the ciphertext. The important point here is that it does not matter which key is applied first, but that both keys are required for the process to work (Figure 1B). Because a pair of keys are required, this approach is also called asymmetric cryptography.

In PKC, one of the keys is designated the public key and may be advertised as widely as the owner wants. The other key is designated the private key and is never revealed to another party. It is straight-forward to send messages under this scheme. Suppose Alice wants to send Bob a message. Alice encrypts some information using Bob's public key; Bob decrypts the ciphertext using his private key. This method could be also used to prove who sent a message; Alice, for example, could encrypt some plaintext with her private key; when Bob decrypts using Alice's public key, he knows that Alice sent the message (authentication) and Alice cannot deny having sent the message (non-repudiation).

Public key cryptography algorithms that are in use today for key exchange or digital signatures include:

  • RSA: The first, and still most common, PKC implementation, named for the three MIT mathematicians who developed it &#; Ronald Rivest, Adi Shamir, and Leonard Adleman. RSA today is used in hundreds of software products and can be used for key F-Secure VPN Plus Client v5.0 crack serial keygen, digital signatures, or encryption of small blocks of data. RSA uses a variable size encryption block and a variable size key. The key-pair is derived from a very large number, n, that is the product of two prime numbers chosen according to special rules; these primes may be or more digits in length each, yielding an n with roughly twice as many digits as the prime factors. The public key information includes n and a derivative of one of the factors of n; an attacker cannot determine the prime factors of n (and, therefore, the private key) from this information alone and that is what makes the RSA algorithm so secure. (Some descriptions of PKC erroneously state that RSA's safety is due to the difficulty in factoring large prime numbers. In fact, large prime numbers, like small prime numbers, only have two factors!) The ability for computers to factor large numbers, and therefore attack schemes such as RSA, is rapidly improving and systems today can find the prime factors of numbers with more than digits. Nevertheless, if a large number is created from two prime factors that are roughly the same size, there is F-Secure VPN Plus Client v5.0 crack serial keygen Jogos de Clique Clique de Graça para Baixar factorization algorithm that will solve the problem in a reasonable amount of time; a test to factor a digit number took years and over 50 years of compute time. InKleinjung et al. reported that factoring a bit (digit) RSA modulus utilizing hundreds of systems took two years and they estimated that a bit RSA modulus would take about a 4Media iPad Max Platinum Crack 5.7.34 Build 20210105 Latest Version times as long. Even so, they suggested that bit RSA be phased out by (See the Wikipedia article on integer factorization.) Regardless, one presumed protection of RSA is that users can easily increase the key size to always stay ahead of the computer processing curve. As an aside, the patent for RSA expired in September which does not appear to have affected RSA's popularity one way or the other. A detailed example of RSA is presented below in Section

  • Diffie-Hellman: After the RSA algorithm was published, Diffie and Hellman came up with their own algorithm. Diffie-Hellman is used for secret-key key exchange only, and not for authentication or digital signatures. More detail about Diffie-Hellman can be found below in Section

  • Digital Signature Algorithm (DSA): The algorithm specified in NIST's Digital Signature Standard (DSS), provides digital signature capability for the authentication of messages. Described in FIPS PUB

  • ElGamal: Designed by Taher Elgamal, ElGamal is a PKC system similar to Diffie-Hellman and used for key exchange. ElGamal is used in some later version of Pretty Good Privacy (PGP) as well as GNU Privacy Guard (GPG) and other cryptosystems.

  • Elliptic Curve Cryptography (ECC): A PKC algorithm based upon elliptic curves. ECC can offer levels of security with small keys comparable to RSA and other PKC methods. It was designed for devices with limited compute power and/or memory, such as smartcards and PDAs. More detail about ECC can be found below in Section Other references include the Elliptic Curve Cryptography page and the Online ECC Tutorial page, both from Certicom. See also RFC for a review of fundamental ECC algorithms and The Elliptic Curve Digital Signature Algorithm (ECDSA) for details about the use of ECC for digital signatures.

  • Identity-Based Encryption (IBE): IBE is a novel scheme first proposed by Adi Shamir in It is a PKC-based key authentication system where the public key can be derived from some unique information based upon the user's identity, allowing two users to exchange encrypted messages without having an a priori relationship. InDan Boneh (Stanford) and Matt Franklin (U.C., Davis) developed a practical implementation of IBE based on elliptic curves and a mathematical construct called the Weil Pairing. In that year, Clifford Cocks (GCHQ) also described another IBE solution based on quadratic residues in composite groups. RFC Identity-Based Cryptography Standard (IBCS) #1 describes an implementation of IBE using Boneh-Franklin (BF) and Boneh-Boyen (BB1) Identity-based Encryption. More detail about Identity-Based Encryption can be found below in Section

  • Public Key Cryptography Standards (PKCS): A set of interoperable standards and guidelines for public key cryptography, designed by RSA Data Security Inc. (These documents are no longer easily available; all links in this section 90Z CD-MP3 Music Converter v1.5 crack serial keygen from storycall.us.)

  • Cramer-Shoup: A public key cryptosystem proposed by R. Cramer and V. Shoup of IBM in

  • Key Exchange Algorithm (KEA): A variation on Diffie-Hellman; proposed as the key exchange method for the NIST/NSA Capstone project.

  • LUC: A public key cryptosystem designed by P.J. Smith and based on Lucas sequences. Can be used for encryption and signatures, using integer factoring.

  • McEliece: A public key cryptosystem based on algebraic coding theory.

For additional information on PKC algorithms, see "Public Key Encryption" (Chapter 8) in Handbook of Applied Cryptography, by A. Menezes, P. van Oorschot, and S. Vanstone (CRC Press, ).


A digression: Who invented PKC? I tried to be careful in the first paragraph of this section to state that Diffie and Hellman "first described publicly" a PKC scheme. Although I have categorized PKC as a two-key system, that has been merely for convenience; the real criteria for a PKC scheme is that it allows two parties to exchange a secret even though the communication with the shared secret might be overheard. There seems to be no question that Diffie and Hellman were first to publish; their method is described in the classic paper, "New Directions in Cryptography," published in the November issue of IEEE Transactions on Information Theory (IT(6), ). As shown in SectionDiffie-Hellman uses the idea that finding logarithms is relatively harder than performing exponentiation. And, indeed, it is the precursor to modern PKC which does employ two keys. Rivest, Shamir, and Adleman described an implementation that extended this idea in their paper, "A Method for Obtaining Digital Signatures and Public Key Cryptosystems," published in the February issue of the Communications of the ACM (CACM), (21(2), ). Their method, of course, is based upon the relative ease of finding the product of two large prime numbers compared to finding the prime factors of a large number.

Diffie and Hellman (and other sources) credit Ralph Merkle with first describing a public key distribution system that allows two parties to share a secret, although it was not a two-key system, per se. A Merkle Puzzle works where Alice creates a large number of encrypted keys, sends them all to Bob so that Bob chooses one at random and then lets Alice know which he has selected. An eavesdropper (Eve) will see all of the keys but can't learn which key Bob has selected (because he has encrypted the response with the chosen key). In this case, Eve's effort to break in is the square of the effort of Bob to choose a key. While this difference may be small it is often sufficient. Merkle apparently took a computer science course at UC Berkeley in and described his method, but had difficulty making people understand it; frustrated, he dropped the course. Meanwhile, he submitted the paper "Secure Communication Over Insecure Channels," which was published in the CACM in April ; Rivest et al.'s paper even makes reference to it. Merkle's method F-Secure VPN Plus Client v5.0 crack serial keygen wasn't published first, but he is often credited to have had the idea first.

An interesting question, maybe, but who really knows? For some time, it was a quiet secret that a team at the UK's Government Communications Headquarters (GCHQ) had first developed PKC in the early s. Because of the nature of the work, GCHQ kept the original memos classified. Inhowever, the GCHQ changed their posture when they realized that there was nothing to gain by continued silence. Documents show that a GCHQ mathematician named James Ellis started research into the key distribution problem in and that byJames Ellis, Clifford Cocks, and Malcolm Williamson had worked out all of the fundamental details of PKC, yet couldn't talk about their work. (They were, of course, barred from challenging the RSA patent!) ByEllis, Cocks, and Williamson began to get their due credit in a break-through article in WIRED Magazine. And the National Security Agency (NSA) claims to have knowledge of this type of algorithm as early as For some additional insight on who knew what when, see Steve Bellovin's "The Prehistory of Public Key Cryptography."


Hash Functions

Hash functions, F-Secure VPN Plus Client v5.0 crack serial keygen, also called message digests and one-way encryption, are algorithms that, in essence, use no key (Figure 1C). Instead, a fixed-length hash value is computed based upon the plaintext that makes it impossible for either the contents or length of the plaintext to be recovered. Hash algorithms are typically used to provide a digital fingerprint of a file's contents, often used to ensure that the file has not been altered by an intruder or virus. Hash functions are also commonly employed by many operating systems to encrypt passwords. Hash functions, then, provide a mechanism to ensure the integrity of a file.

Hash functions are also designed so that small changes in the input produce significant differences in the hash value, for example:

Hash string 1: The quick brown fox jumps over the lazy dog
Hash string 2: The quick brown fox jumps over the lazy dog.

MD5 [hash string 1] = 37c4b87edffc5dff5acee7ee09
MD5 [hash string 2] = 0dcde94cfe1d2ae0c8e

SHA1 [hash string 1] = beb5c3c5c1d9bcb2e7cdd76b
SHA1 [hash string 2] = 9c04cde9b11f70cacdce4b

RIPEMD [hash string 1] = eefdda9e2cff
RIPEMD [hash string 2] = 99bacdbe25bbee


Let me reiterate that hashes are one-way encryption. You cannot take a hash and "decrypt" it to find the original string that created it, despite the many web sites that claim or suggest otherwise, such as CrackStation, storycall.us, MD5 Online, md5thiscracker, OnlineHashCrack, and RainbowCrack.

Note that these sites search databases and/or use rainbow tables to find a suitable string that produces the hash in question but one can't definitively guarantee what string originally produced the hash. This is an important distinction. Suppose that you want to crack someone's password, where the hash of the password is stored on the server. Indeed, all you then need is a string that produces the correct hash and you're in! However, you cannot prove that you have discovered the user's password, only a "duplicate key."


Hash algorithms in common use today include:

  • Message Digest (MD) algorithms: A series of byte-oriented algorithms that produce a bit hash value from an arbitrary-length message.

    • MD2 (RFC ): Designed for systems with limited memory, such as smart cards. (MD2 has been relegated to historical status, per RFC )

    • MD4 (RFC ): Developed Category Archives: MAC Rivest, similar to MD2 but designed specifically for fast processing in software. (MD4 has been relegated to historical status, per RFC )

    • MD5 (RFC ): Also developed by Rivest after potential weaknesses were reported in MD4; this scheme is similar to MD4 but is slower because more manipulation is made to the original data. MD5 has been implemented in a large number of products although several weaknesses in the algorithm were demonstrated by German cryptographer Hans Dobbertin in ("Cryptanalysis of MD5 Compress"). (Updated security considerations for MD5 can be found in RFC )

  • Secure Hash Algorithm (SHA): Algorithm for NIST's Secure Hash Standard (SHS), described in FIPS PUB The status of NIST hash algorithms can be found on their "Policy on Hash Functions" page.

    • SHA-1 produces a bit hash value and was originally published as FIPS PUB and RFC SHA-1 was deprecated by NIST as of the end of although it is still widely used.

    • SHA-2, originally described in FIPS PUB and eventually replaced by FIPS PUB (and FIPS PUB Let Me Die (inside) Free Download, comprises five algorithms in the SHS: SHA-1 plus SHA, SHA, SHA, and SHA which can produce hash values that are,or bits in length, respectively. SHA-2 recommends use of SHA-1, F-Secure VPN Plus Client v5.0 crack serial keygen, SHA, and SHA for messages less than 264 bits in length, and employs a bit block size; SHA and SHA are recommended for messages less than 2 bits in length, and employs a 1, bit block size. FIPS PUB also introduces the concept of a truncated hash in SHA/t, a generic name referring to a hash value based upon the SHA algorithm that has been truncated to t bits; SHA/ and SHA/ are specifically described. SHA, and are also described in RFC

    • SHA-3 is the current SHS algorithm. Although there had not been any successful attacks on SHA-2, NIST decided that having an alternative to SHA-2 using a different algorithm would be prudent. InF-Secure VPN Plus Client v5.0 crack serial keygen, they launched a SHA-3 Competition to find that alternative; a list of submissions can be found at The SHA-3 Zoo. InNIST announced Code Vein 1.01 Crack Archives after reviewing 64 submissions, the winner was Keccak (pronounced "catch-ack"), a family of hash algorithms based on sponge functions. The NIST version can support hash output sizes of and bits.

  • RIPEMD: A series of message digests that initially came from the RIPE (RACE Integrity Primitives Evaluation) project. RIPEMD was designed by Hans Dobbertin, Antoon Bosselaers, and Bart Preneel, and optimized for bit processors to replace the then-current bit hash functions. Other versions include RIPEMD, RIPEMD, and RIPEMD

  • eD2k: Named for the EDonkey Network (eD2K), the eD2k hash is a root hash of an MD4 hash list of a given file. A root hash is used on peer-to-peer file transfer networks, where a file is broken into chunks; each chunk has its own MD4 hash associated with it and the server maintains a file that contains the hash list of all of the chunks. The root hash is the hash of the hash list file.

  • HAVAL (HAsh of VAriable Length): Designed by Y. Zheng, J. Pieprzyk and J. Seberry, PiratePC | Cracked PC Software For Free! - Part 2 hash algorithm with many levels of security. HAVAL can create hash values that are, or bits in length. More details can be found in "HAVAL - A one-way hashing algorithm with variable length output" by Zheng, Pieprzyk, and Avast Driver Updater Crack 2021 [v2.7] With Activation Code Download (AUSCRYPT '92).

  • The Skein Hash Function Family: The Skein Hash Function Family was proposed to NIST in their hash function competition. Skein is F-Secure VPN Plus Client v5.0 crack serial keygen due to using just a few simple computational primitives, secure, and very flexible &#; per the specification, it can be used as a straight-forward hash, MAC, HMAC, digital signature hash, key derivation mechanism, stream cipher, or pseuo-random number generator. Skein supports internal state sizes ofand bits, and arbitrary output lengths.

  • SM3: SM3 is a bit hash function operating on bit input blocks. Part of a Chinese National Standard, SM3 is issued by the Chinese State Cryptographic Authority as GM/T SM3 cryptographic hash algorithm () and GB/T Information security techniques—SM3 cryptographic hash algorithm (). More information can also be found at the SM3 (hash function) page.

  • Tiger: Designed by Ross Anderson and Eli Biham, Tiger is designed to be secure, run efficiently on bit processors, and easily replace MD4, MD5, SHA and SHA-1 in other applications. Tiger/ produces a bit output and is compatible with bit architectures; Tiger/ and Tiger/ produce a hash of length and bits, respectively, to provide compatibility with the other hash functions mentioned above.

  • Whirlpool: Designed by V, F-Secure VPN Plus Client v5.0 crack serial keygen. Rijmen (co-inventor of Rijndael) and P.S.L.M. Barreto, Whirlpool is one of two hash functions endorsed by the NESSIE competition (the other being SHA). Whirlpool operates on messages less than 2 bits in length and produces a message digest of bits. The design of this hash function is very different than that of MD5 and SHA-1, making it immune to the types of attacks that succeeded on those hashes.

Readers might be interested in HashCalc, a Windows-based program that calculates hash values using a dozen algorithms, including MD5, SHA-1 and several variants, RIPEMD, and Tiger. Command line utilities that calculate hash values include sha_verify by Dan Mares (Windows; supports MD5, SHA-1, SHA-2) and md5deep (cross-platform; supports MD5, SHA-1, SHA, Tiger, and Whirlpool).


A digression on hash collisions. Hash functions are sometimes misunderstood and some Easyworship 2009 1.9 crack serial keygen claim that no two files can have the same hash value. This is in theory, if not in fact, incorrect. Consider a hash function that provides a bit hash value. There are, F-Secure VPN Plus Client v5.0 crack serial keygen, then, 2 possible hash values. But there are an infinite number of possible files and &#; >> 2. Therefore, there have to be multiple files &#; in F-Secure VPN Plus Client v5.0 crack serial keygen, there have to be an infinite number of files! &#; that have the same bit hash value. (Now, while even this is theoretically correct, it is not true in practice because hash algorithms are designed to work with a limited message size, as mentioned above. For example, SHA-1, SHA, and SHA produce hash values that are, and bits in length, respectively, and limit the message length to less than 264 bits; SHA and all SHA variants limit the message length to less than 2 bits. Nevertheless, F-Secure VPN Plus Client v5.0 crack serial keygen, hopefully you get my point &#; and, alas, even if you don't, do know that there are multiple files that have the same MD5 or SHA-1 hash values.)

The difficulty is not necessarily in finding two files with the same hash, but in finding a second file that has the same hash value as a given first file. Consider this example. A human head has, generally, no more than ~, hairs. Since there are more than 7 billion people on earth, we know that there are a lot of people with the same number of hairs on their head. Finding two people with the same number of hairs, then, would be relatively simple. The harder problem is choosing one person (say, you, the reader) and then finding another person who has the same number of hairs on their head as you have on yours.

This is somewhat similar to the Birthday Problem. We know from probability that if you choose a random group of ~23 people, the probability is about 50% that two will share a birthday (the probability goes up to % with a group of 70 people). However, if you randomly select one person in a group of 23 and try to find a match to that person, the probability is only about 6% of finding a match; you'd need a group of for a 50% probability of a shared birthday to one of the people chosen at random (and a group of more than 4, to obtain a % probability).

What is hard to do, then, is to try to create a file that matches a given hash value so as to force a hash value collision &#; which is the reason that hash functions are used extensively for information security and computer forensics applications. Alas, researchers as far back as found that practical collision attacks could be launched on MD5, SHA-1, and other hash algorithms and, F-Secure VPN Plus Client v5.0 crack serial keygen, today, it is generally recognized that MD5 and SHA-1 are pretty much broken. Readers interested in this problem should read the following:

  • AccessData. (, April). MD5 Collisions: The Effect on Computer Forensics, F-Secure VPN Plus Client v5.0 crack serial keygen. AccessData White Paper.
  • Burr, W. (, March/April). Cryptographic hash standards: Where do we go from here?IEEE Security & Privacy, 4(2),
  • Dwyer, D. (, June 3). SHA-1 Collision Attacks Now 252. SecureWorks Research blog.
  • Gutman, P., Naccache, D., & Palmer, C.C. (, May/June). When hashes collide, F-Secure VPN Plus Client v5.0 crack serial keygen. IEEE Security & Privacy, 3(3),
  • Kessler, G.C. (). The Impact of MD5 File Hash Collisions on Digital Forensic Imaging. Journal of Digital Forensics, Security & Law, 11(4),
  • Kessler, G.C. (). The Impact of SHA-1 File Hash Collisions on Digital Forensic Imaging: A Follow-Up Experiment. Journal of Digital Forensics, Security & Law, 11(4),
  • Klima, V. (, March). Finding MD5 Collisions - a Toy For a Notebook.
  • Lee, R. (, January 7). Law Is Not A Science: Admissibility of Computer Evidence and MD5 Hashes. SANS Computer Forensics blog.
  • Leurent, G. & Peyrin, T. (, January). SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust. Real World Crypto .
  • Leurent, G. & Peyrin, T. (, January). SHA-1 is a Octoplus Suite v1.5.6 Archives First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust.(paper)
  • Stevens, M., F-Secure VPN Plus Client v5.0 crack serial keygen, Bursztein, E., Karpman, P., Albertini, A., F-Secure VPN Plus Client v5.0 crack serial keygen, & Markov, Y. (). The first collision for full SHA
  • Stevens, M., Karpman, P., & Peyrin, T, F-Secure VPN Plus Client v5.0 crack serial keygen. (, October 8). Freestart collision on full SHA Cryptology ePrint Archive, Report /
  • Thompson, E. (, February). MD5 collisions and the impact on computer forensics. Digital Investigation, 2(1),
  • Wang, X., Feng, D., Lai, X., & Yu, H. (, August). Collisions for Hash Functions MD4, F-Secure VPN Plus Client v5.0 crack serial keygen, MD5, HAVAL and RIPEMD.
  • Wang, X., Yin, Y.L., & Yu, H. (, February 13), F-Secure VPN Plus Client v5.0 crack serial keygen. Collision Search Attacks on SHA1.

Readers are also referred to the Eindhoven University of Technology HashClash Project Web site. for For additional information on hash functions, see David Hopwood's MessageDigest Algorithms page and Peter Selinger's MD5 Collision Demo page, F-Secure VPN Plus Client v5.0 crack serial keygen. For historical purposes, take a look at the situation with hash collisions, circain RFC

In Octoberthe SHA-1 Freestart Collision was announced; see a report by Bruce Schneier and the developers of the attack (as well as the paper above by Stevens et al. ()). In Februarythe first SHA-1 collision was announced on the Google Security Blog Kaspersky Antivirus Crack with Activation Key 2021 [Lifetime] Download Centrum Wiskunde & Informatica's Shattered page. See also the paper by Stevens et al. (), listed above, F-Secure VPN Plus Client v5.0 crack serial keygen. If ths isn't enough, see the SHA-1 is a Shambles Web page and the Leurent & Peyrin paper, listed above.

For an interesting twist on this discussion, read about the Nostradamus attack reported at Predicting the winner of the US Presidential Elections using a Sony PlayStation 3 (by M. Stevens, F-Secure VPN Plus Client v5.0 crack serial keygen, A.K. Lenstra, and B. de Weger, November ).


Finally, note that certain extensions of hash functions are used for a variety of information security and digital forensics applications, such as:

  • Hash libraries, aka hashsets, are sets of hash values corresponding to known files, F-Secure VPN Plus Client v5.0 crack serial keygen. A hashset containing the hash values of all files known to be a part of a given operating system, for example, could form a set of known good files, and could be ignored in an investigation for malware or other suspicious file, whereas as hash library of known child pornographic images could form a set of known bad files and be the target of such an investigation.
  • Rolling hashes refer to a set of hash values that are computed based upon a fixed-length "sliding window" through the input. As an example, a hash value might be computed on bytes of a file, then on bytes,etc.
  • Fuzzy hashes are an area of intense research and represent hash values that represent two inputs that are similar. Fuzzy hashes are used to detect documents, images, or other files that are close to each other with respect to content. See "Fuzzy Hashing" by Jesse Kornblum for a good treatment of this topic.

Why Three Encryption Techniques?

So, why are there so many different types of cryptographic schemes? Why can't we do everything we need with just one?

The answer is that each scheme is optimized for some specific cryptographic application(s). Hash functions, for example, are well-suited for ensuring data integrity because any change made to the contents of a message will result in the receiver calculating a different hash value than the one placed in the transmission by the sender. Since it is highly unlikely that two different messages will yield the same hash value, data integrity is ensured to a high degree of confidence.

Secret key cryptography, on the other hand, is ideally suited to encrypting messages, thus providing privacy and confidentiality. The sender can generate a session key on a per-message basis to encrypt the message; the receiver, of course, needs the same session key in order to decrypt the message.

Key exchange, of course, is a key application of public key cryptography (no pun intended). Asymmetric schemes can also be used for non-repudiation and user authentication; if the receiver can obtain the session key encrypted with the sender's private key, then F-Secure VPN Plus Client v5.0 crack serial keygen this sender could have sent the message. Public key cryptography could, theoretically, also be used to encrypt messages although this is rarely done because secret key cryptography values can generally be computed about times faster than public key cryptography values.

FIGURE 4: Use of the three cryptographic techniques for secure communication.


Figure 4 puts all of this together and shows how a hybrid cryptographic scheme combines all of these functions to form a secure transmission comprising a digital signature and digital envelope. In this example, the sender of the message is Alice and the receiver is Bob.

A digital envelope comprises an encrypted message and an encrypted session key. Alice uses secret key cryptography to encrypt her message using the session key, which she generates at random with each session. Alice then encrypts the session key using Bob's public key. The encrypted message and encrypted session key together form the digital envelope. Upon receipt, Bob recovers the session secret key using his private key and then decrypts the encrypted message.

The digital signature is formed in two steps. First, Alice computes the hash value of her message; next, she encrypts the hash value with her private key. Upon receipt of the digital signature, Bob recovers the hash value calculated by Alice by decrypting the digital signature with Alice's public key. Bob can then apply the hash function to Alice's original message, which Active Password Changer 11.0 Crack Full Latest Download 2021 has already decrypted (see previous paragraph). If the resultant hash value is not the same as the value supplied by Alice, then Bob knows that the message has been altered; if the hash values are the same, Bob should believe that the message he received is identical to the one that Alice sent.

This scheme also provides nonrepudiation since it proves that Alice sent the message; if the hash value recovered by Bob using Alice's public key proves that the message has not been altered, then only Alice could have created the digital signature. Bob also has proof that he is the intended receiver; if he can correctly decrypt the message, then he must have correctly decrypted the session key meaning that his is the correct private key.

This diagram purposely suggests a cryptosystem where the session key is used for just a single session. Even F-Secure VPN Plus Client v5.0 crack serial keygen this session key is somehow broken, only this session will be compromised; the session key for the next session is not based upon the key for this session, just as this session's key was not dependent on the key from the previous session. This is known as Perfect Forward Secrecy; you might lose one session key due to a compromise but you won't lose all of them. (This was an issue in the OpenSSL vulnerability known as Heartbleed.)

The Significance of Key Length

In a article in the industry literature, a writer made the claim that bit keys did not provide as adequate protection for DES at that time as they did in because computers were times faster in than in Therefore, the writer went on, we needed 56,bit keys in instead of bit keys to provide adequate protection. The conclusion was then drawn that because 56,bit keys are infeasible (true), F-Secure VPN Plus Client v5.0 crack serial keygen, we should accept the fact that we have to live with weak cryptography F-Secure VPN Plus Client v5.0 crack serial keygen. The major error here is that the writer did not take into account that the number of possible key values double whenever a single bit is added to the key length; thus, a bit key has twice as many values as a bit key (because 257 is two times 256). In fact, a bit key would have times more values than a bit key.

But this does bring up the question &#; "What is the significance of key length as it affects the level of protection?"

In cryptography, size does matter. The larger the key, the harder it is to crack a block of encrypted data. The reason that large keys offer more protection is almost obvious; computers have made it easier to attack ciphertext by using brute force methods rather than by attacking the mathematics (which are generally well-known anyway). With a brute force attack, the attacker merely generates every possible key and applies it to the ciphertext. Any resulting plaintext that makes sense offers a candidate for a legitimate key. This was the basis, of course, of the EFF's attack on DES.

Until the mids or so, brute force attacks were beyond the capabilities of computers that were within the budget of the attacker community. By that time, however, significant compute power was typically available and accessible. General-purpose computers such as PCs were already being used for brute force attacks. For serious attackers with money to spend, such as some large companies or governments, Field Programmable Gate Array (FPGA) or Application-Specific Integrated Circuits (ASIC) technology offered the ability to build specialized chips that could provide even faster and cheaper solutions than a PC, F-Secure VPN Plus Client v5.0 crack serial keygen. As an example, the AT&T Optimized Reconfigurable Cell Array (ORCA) FPGA chip cost about $ and could test F-Secure VPN Plus Client v5.0 crack serial keygen million DES keys per second, while a $10 ASIC chip could test million DES keys per second; compare that to a PC which might be able to test 40, keys per second. Distributed attacks, harnessing the power of up to tens of thousands of powerful CPUs, are now commonly employed to try to brute-force crypto keys.

Type of AttackerBudgetToolTime and Cost
Per Key Recovered
Key Length Needed
For Protection
In Late
40 bits56 bits
Pedestrian HackerTinyScavenged
computer
time
1 weekInfeasible45
$FPGA5 hours
($)
38 years
($5,)
50
Small Business$10,FPGA12 minutes
($)
18 months
($5,)
55
Corporate Department$KFPGA24 seconds
($)
19 days
($5,)
60
ASIC seconds
($)
3 hours
($38)
Big Company$10MFPGA7 seconds
($)
13 hours
($5,)
70
ASIC seconds
($)
6 minutes
($38)
Intelligence Agency$MASIC seconds
($)
12 seconds
($38)
75

Table 2 &#; from a article discussing both why exporting Need For Speed Shift 2 Unleashed crack serial keygen keys was, in essence, no crypto at all and why DES' days were numbered &#; shows what DES key sizes were needed to protect data from attackers with different time and financial resources. This information was not merely academic; one of the basic tenets of any security system is to have an idea of what you are protecting and from whom are you protecting it! The table clearly shows that a bit key was essentially worthless against even the most unsophisticated attacker. On the other hand, bit keys were fairly strong unless you might be subject to some pretty serious corporate or government espionage. But note that even bit keys were clearly on the decline in their value and that the times in the table were worst cases.

So, how big is big enough? DES, invented inwas still in use at the turn of the century, nearly 25 years later. If we take that to be a design criteria (i.e., a plus year lifetime) and we believe Moore's Law ("computing power doubles every 18 months"), then a key size extension of 14 bits (i.e., a factor of more than 16,) should be adequate. The DES proposal suggested bit keys; bya bit key would have been required to offer equal protection and an bit key necessary by

A or bit SKC key will probably suffice for some time because that length keeps us ahead of the brute force capabilities of the attackers. Note that while a large key is good, a huge key may not always be better; for example, expanding PKC keys beyond the current or bit lengths doesn't add any necessary protection at this time. Weaknesses in cryptosystems are largely based upon key management rather than weak keys.

Much of the discussion above, including the table, is based on the paper "Minimal Key Lengths for Symmetric Ciphers to Provide Adequate Commercial Security" by M, F-Secure VPN Plus Client v5.0 crack serial keygen. Blaze, W. Diffie, R.L. Rivest, B. Schneier, T. Shimomura, E. Thompson, and M. Wiener ().

The most effective large-number factoring methods today use a mathematical Number Field Sieve to find a certain number of relationships and then uses a matrix operation to solve a linear equation to produce the two prime factors. The sieve step actually involves a large number of operations that can be performed in parallel; solving the linear equation, however, requires a supercomputer. Indeed, finding the solution to the RSA challenge in F-Secure VPN Plus Client v5.0 crack serial keygen &#; factoring a digit (bit) prime number &#; required computers across the Internet about 4 weeks for the first step and a Cray computer hours and MB of memory to do the second step.

In earlyShamir (of RSA fame) described a new machine that could increase factorization speed by orders of magnitude. Although no detailed plans were provided nor is one known to have been built, the concepts of TWINKLE (The Weizmann Institute Key Locating Engine) could result in a specialized piece of hardware that would cost about $ and have the processing power of PCs. There still appear to be many engineering details that have to F-Secure VPN Plus Client v5.0 crack serial keygen worked out before such a machine could be built. Furthermore, the hardware improves the sieve step only; the matrix operation is not optimized at all by this design and the complexity of this step grows rapidly with key length, both in terms of processing time and memory requirements. Nevertheless, this plan conceptually puts bit keys within reach of being factored. Although most PKC schemes allow keys that are bits and longer, Shamir claims that bit RSA keys "protect 95% of today's E-commerce on the Internet." (See Bruce Schneier's Crypto-Gram (May 15, ) for more information.)

It is also interesting to note that while cryptography is good and strong cryptography is better, long keys may disrupt the nature of the randomness of data files. Shamir and van Someren ("Playing hide and seek with stored keys") have noted that a new generation of viruses can be written that will find files encrypted with long keys, making them easier to find by intruders and, therefore, more prone to attack.

Finally, U.S. government policy has tightly controlled the export of crypto products since World War II. Until the mids, export outside of North America of cryptographic products using keys greater than 40 bits in length was prohibited, which made those products essentially worthless in the marketplace, particularly for electronic commerce; today, crypto products are widely available on the Internet without restriction. The U.S. Department of Commerce Bureau of Industry and Security maintains an Encryption FAQ web page with more information about the current state of encryption registration.


Without meaning to editorialize too much in this tutorial, a bit of historical context might be helpful. In the mids, the U.S. Department of Commerce still classified cryptography as a munition and limited the export of any products that contained crypto. For that reason, browsers in the era, such as Internet Explorer and Netscape, had a domestic version with bit encryption (downloadable only in the U.S.) and an export version with bit encryption. Many cryptographers felt that the export limitations should be lifted because they only applied to U.S. products and seemed to have been put into place by policy makers who believed that only the U.S. knew how to build strong crypto algorithms, ignoring the work ongoing in Australia, Canada, Israel, South Africa, the U.K., and other locations in the s, F-Secure VPN Plus Client v5.0 crack serial keygen. Those restrictions were lifted by orbut there is still a prevailing attitude, apparently, that U.S. crypto algorithms are the only strong ones F-Secure VPN Plus Client v5.0 crack serial keygen consider Bruce Schneier's blog in June titled "CIA Director John Brennan Pretends Foreign Cryptography Doesn't Exist." Cryptography is a decidedly international game today; note the many countries mentioned above as having developed various algorithms, not the least of which is the fact that NIST's Advanced Encryption Standard employs an algorithm submitted by cryptographers from Belgium. For more evidence, see Schneier's Worldwide Encryption Products Survey (February ).


On a related topic, public key crypto schemes can be used for several purposes, including key exchange, digital signatures, authentication, and more. In those PKC systems used for SKC key exchange, the PKC key lengths are chosen so as to be resistant to some selected level of attack. The length of the secret keys exchanged via that system have to have at least the same level of attack resistance. Thus, the three parameters of such a system &#; system strength, secret key strength, and public key strength &#; must be matched. This topic is explored in more detail in Determining Strengths For Public Keys Used For Exchanging Symmetric Keys (RFC ).

4. TRUST MODELS

Secure use of cryptography requires trust. While secret key cryptography can ensure message confidentiality and hash codes can ensure integrity, none of F-Secure VPN Plus Client v5.0 crack serial keygen works without trust. In SKC, Alice and Bob had to share a secret key. PKC solved the secret distribution problem, but how does Alice really know that Bob is who he says he is? Just because Bob has a public and private key, and purports to be "Bob," how does Alice know that a malicious person (Mallory) is not pretending to be Bob?

There are a number of trust models employed by various cryptographic schemes. This section will explore three of them:

  • The web of trust employed by Pretty Good Privacy (PGP) users, who hold their own set of trusted public keys.
  • Kerberos, a secret key distribution scheme using a trusted third party.
  • Certificates, which allow a set of trusted third parties to authenticate each other and, by implication, each other's users.

Each of these trust models differs in complexity, general applicability, scope, and scalability.

PGP Web of Trust

Pretty Good Privacy (described more below in Section ) is a widely used private e-mail scheme based on public key methods. A PGP user maintains a local keyring of all their known and trusted public keys. The user makes their own determination about the trustworthiness of a key using what is called a "web of trust."

FIGURE 5: GPG keychain.

Figure 5 shows a PGP-formatted keychain from the GNU Privacy Guard (GPG) software, an implementation of the OpenPGP standard. This is a section of my keychain, so only includes public keys from individuals whom I know and, presumably, trust. Note that keys are associated with e-mail addresses rather than individual names.

In general, the PGP Web of trust works as follows. Suppose that Alice needs Bob's public key. Alice could just ask Bob for it directly via e-mail or download the public key from a PGP key server; this server might a well-known PGP key repository or a site that Bob maintains himself. In fact, Bob's public key might be stored or listed in many places. (My public key, for example, can be found at storycall.us or at several public PGP key servers, including storycall.us.) Alice is prepared to believe that Bob's public key, as stored at these locations, is valid.

Suppose Carol claims to hold Bob's public key and offers to give the key to Alice. How does Alice know that Carol's version of Bob's key is valid or if Carol is actually giving Alice a key that will allow Mallory access to messages? The answer is, "It depends." If Alice trusts Carol and Carol says that she thinks that her version of Bob's key is valid, then Alice may &#; at her option &#; trust that key. And trust is not necessarily transitive; if Dave has a copy of Bob's key and Carol trusts Dave, it does not necessarily follow that Alice trusts Dave even if she does trust Carol.

The point here is that who Alice trusts and how she makes that determination is strictly up to Alice. PGP makes no statement and has no protocol about how one user determines whether they trust another user or not. In any case, encryption and signatures based on public keys can only be used when the appropriate public key is on the user's keyring.

Kerberos

Kerberos is a commonly used authentication scheme on the Internet. Developed by MIT's Project Athena, Kerberos is named for the three-headed dog who, according to Greek mythology, guards the entrance of Hades (rather than the exit, for some reason!).

Kerberos employs a client/server architecture and provides user-to-server authentication rather than host-to-host authentication. In 4K YouTube to MP3 4.2.1.4460 Full Crack model, security and authentication will be based on secret key technology where every host on the network has its own secret key. It would clearly be unmanageable if every host had to know the keys of all other hosts so a secure, trusted host somewhere on the network, known as a Key Distribution Center (KDC), knows the keys for all of the hosts (or at least some of the hosts within a portion of the network, F-Secure VPN Plus Client v5.0 crack serial keygen, called a realm). In this way, when a new node is brought online, only the KDC and the new node need to be configured with the node's key; keys can be distributed physically or by some other secure means.

FIGURE 6: Kerberos architecture.


The Kerberos Server/KDC has two main functions (Figure 6), known as the Authentication Server (AS) and Ticket-Granting Server (TGS). The steps in establishing an authenticated session between an application client and the application server are:
  1. The Kerberos client software establishes a connection with the Kerberos server's AS function. The AS first authenticates that the client is who it purports to be. The AS then provides the client with a secret key for this login session (the TGS session key) and a ticket-granting ticket (TGT), which gives the client permission to talk to the TGS. The ticket has a finite lifetime so that the authentication process is repeated periodically.
  2. The client now communicates with the TGS to obtain the Application Server's key so that it (the client) can establish a connection to the service it wants. The client supplies the TGS with the TGS session key and TGT; the TGS responds with an application session key (ASK) and an encrypted form of the Application Server's secret key; this secret key is never sent on the network in any other form.
  3. The client has now authenticated itself and can prove its identity to the Application Server by supplying the Kerberos ticket, application session key, and encrypted Application Server secret key. The Application Server responds with similarly encrypted information to authenticate itself to the client. At this point, F-Secure VPN Plus Client v5.0 crack serial keygen, the client can initiate the intended service requests (e.g., Telnet, FTP, HTTP, or e-commerce transaction session establishment).

The current version of this protocol is Kerberos V5 (described in RFC ). While the details of their operation, functional capabilities, and message formats are different, the conceptual overview above pretty much holds for both. One primary difference is that Kerberos V4 uses only DES to generate keys and encrypt messages, while V5 allows other schemes to be employed (although DES is still the most widely algorithm used).

Public Key Certificates and Certificate Authorities

Certificates and Certificate Authorities (CA) are necessary for widespread use of cryptography for e-commerce applications. While a combination of secret and public key cryptography can solve the business issues discussed above, crypto cannot alone address the trust issues that must exist between a customer and vendor in the very fluid, very dynamic e-commerce relationship. How, for example, does one site obtain another party's public key? How does a recipient determine if a public key really belongs to the sender? How does the recipient know that the sender is using their public key for a legitimate purpose for which they are Loaris Trojan Remover Crack 2021 [v3.1.74] With License Key Download When does a public key expire? How can a key be revoked in case of compromise or loss?

The basic concept of a certificate is one that is familiar to all of us. A driver's license, credit card, or SCUBA certification, for example, identify us to others, indicate something that we are authorized to do, have an expiration date, and identify the authority that granted the certificate.

As complicated as this may sound, it really isn't. Consider driver's licenses, F-Secure VPN Plus Client v5.0 crack serial keygen. I have one issued by the State of Florida. The license establishes my identity, indicates the type of vehicles that I can operate and the fact that I must wear corrective lenses while doing so, identifies the issuing authority, and notes that I am an organ donor. When I drive in other states, the other jurisdictions throughout the U.S. recognize the authority of Florida to issue this "certificate" and they trust the information it contains. When I leave the U.S., everything changes. When I am in Aruba, Australia, Canada, Israel, and many other countries, they will accept not the Florida license, per se, but any license issued in the U.S. This analogy represents the certificate trust chain, where even certificates carry certificates.

For purposes of electronic transactions, certificates are digital documents. The specific functions of the certificate include:

  • Establish identity: Associate, or bind, a public key to an individual, organization, corporate position, or other entity.
  • Assign authority: Establish what actions the holder may or may not take based upon this certificate.
  • Secure confidential information (e.g., encrypting the session's symmetric key for data confidentiality).

Typically, a certificate contains a public key, a name, an expiration date, the name of the authority that issued the certificate (and, therefore, is vouching for the identity of the user), a serial number, any pertinent policies describing how the certificate was issued and/or how the certificate may be used, the digital signature of the certificate issuer, and perhaps other information.

FIGURE 7: VeriSign Class 3 certificate.

A sample abbreviated certificate is shown in Figure 7. This is a typical certificate found in a browser, in this case, Mozilla Firefox (MacOS). While this is a certificate issued by VeriSign, many root-level certificates can be found shipped with browsers. F-Secure VPN Plus Client v5.0 crack serial keygen the browser makes a connection to a secure Web site, the Web server sends its public key certificate to the browser, F-Secure VPN Plus Client v5.0 crack serial keygen. The browser then checks the certificate's signature against the public key that it has stored; if there is a match, the certificate is taken as valid and the Web site verified by this certificate is considered to be "trusted."

The most widely accepted certificate format is the one defined F-Secure VPN Plus Client v5.0 crack serial keygen International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Recommendation X Rec. X is a specification used around the world and any applications complying with X can share certificates. Most certificates today comply with X Version 3 and contain the following information:

  • Version number
  • Certificate serial number
  • Signature algorithm identifier
  • Issuer's name and unique identifier
  • Validity (or operational) period
  • Subject's name and unique identifier
  • Subject public key information
  • Standard extensions
    • Certificate appropriate use definition
    • Key usage limitation definition
    • Certificate policy information
  • Other extensions
    • Application-specific
    • CA-specific

Certificate authorities are the repositories for public keys and can be any agency that issues certificates. A company, for example, may issue certificates to its employees, a college/university to its students, a store to its customers, an Internet service provider to its users, or a government to its constituents.

When a sender needs an intended receiver's public key, the sender must get that key from the receiver's CA. That scheme is straight-forward if the sender and receiver have certificates issued by the same CA. If not, how does the sender know to trust the foreign CA? One industry wag has noted, about trust: "You are either born with it or have it granted upon you." Thus, some CAs will be trusted because they are known to be reputable, such as the CAs operated by AT&T Services, Comodo, DigiCert (formerly GTE Cybertrust), F-Secure VPN Plus Client v5.0 crack serial keygen, EnTrust, Broadcom (formerly Symantec, formerly VeriSign), and Thawte. CAs, in turn, form trust relationships with other CAs. Thus, if a user queries a foreign CA for information, the user may ask to see a list of CAs that establish a "chain of trust" back to the user.

One major feature to look for in a CA is their identification policies and procedures. When a user generates a key pair F-Secure VPN Plus Client v5.0 crack serial keygen forwards the public key to a CA, the CA has to check the sender's identification and takes any steps necessary to assure itself that the request is really coming from the advertised sender. Different CAs have different identification policies and will, therefore, be trusted differently by other CAs. Verification of identity is just one of many issues that are part of a CA's Certification Practice Statement (CPS) and policies; other issues include how the CA protects the public keys in its care, how lost or compromised keys are revoked, and how the CA protects its own private keys.

As a final note, CAs are not immune to attack and certificates themselves are able to be counterfeited. One of the first such episodes occurred at the turn of the century; on January 29 and 30,two VeriSign Class 3 code-signing digital certificates were issued to an individual who fraudulently claimed to be a Microsoft employee (CERT/CC CA and Microsoft Security Bulletin MS - Critical). Problems have continued over the years; good write-ups on this can be found at "Another Certification Authority Breached (the 12th!)" and "How Cybercrime Exploits Digital Certificates." Readers are also urged to read "Certification Authorities Under Attack: A Plea for Certificate Legitimation" (Oppliger, R., January/FebruaryIEEE Internet Computing, 18(1), ).

As a partial way to address this issue, the Internet Security Research Group (ISRG) designed the Automated Certificate Management Environment (ACME) protocol. ACME is a communications protocol that streamlines the process of deploying a Public Key Infrastructure (PKI) by automating interactions between CAs and Web servers that wish to obtain a certificate. More information can be found at the Let's Encrypt Web site, an ACME-based CA service provided by the ISRG.

Summary

The paragraphs above describe three very different trust models. It is hard to say that any one is better than the others; it depends upon your application. One of the biggest and fastest growing applications of cryptography today, though, is electronic commerce (e-commerce), a term that itself begs for a formal definition.

PGP's web of trust is easy to maintain and very much based on the reality of users as people. The model, however, is limited; just how many public keys can a single user reliably store and maintain? And what if you are using the "wrong" computer when you want to send a message and can't access your keyring? How easy it is to revoke a key if it is compromised? PGP may also not scale well to an e-commerce scenario of secure communication between total strangers on short-notice.

Kerberos overcomes many of the problems of PGP's web of trust, in that it is scalable and its scope can be very large. However, it also requires that the Kerberos server have a priori knowledge of all client systems prior to any transactions, which makes it unfeasible for "hit-and-run" client/server relationships as seen in e-commerce.

Certificates and the collection of CAs will form a PKI. In the early days of the Internet, every host had to maintain a list of every other host; the Domain Name System (DNS) introduced the idea of a distributed database for this purpose and the DNS is one of the key reasons that the Internet has grown as it has. A PKI will fill a similar void in the e-commerce and PKC realm.

While certificates and the benefits of a PKI are most often associated with electronic commerce, the applications for PKI are much broader and include secure electronic mail, payments and electronic checks, Electronic Data Interchange (EDI), secure transfer of Domain Name System (DNS) and routing information, electronic forms, and digitally signed documents. A single "global PKI" is still many years away, that is the ultimate goal of today's work as international electronic commerce changes the way in which we do business in a similar way in which the Internet has changed the way in which we communicate.

5. CRYPTOGRAPHIC ALGORITHMS IN ACTION

The paragraphs above have provided an overview of the different types of cryptographic algorithms, as well as some examples of some available protocols and schemes. Table 3 provides a list of some other noteworthy schemes and cryptosystems employed &#; or proposed &#; for a variety of functions, most notably electronic commerce and secure communication. The paragraphs below will show several real cryptographic applications that many of us employ (knowingly or not) everyday for password protection and private communication. Some of the schemes described below never were widely deployed but are still historically interesting, thus remain included here. This list is, by no means, exhaustive but describes items that are of significant current and/or historic importance (a subjective judgement, to be sure).

BitmessageA decentralized, encrypted, peer-to-peer, trustless communications protocol for message exchange. The decentralized design, outlined in "Bitmessage: A Peer-to-Peer Message Authentication and Delivery System" (Warren, ), is conceptually based on the Bitcoin model.
CapstoneA now-defunct U.S. National Institute of Standards and Technology (NIST) and National Security Agency (NSA) project under the Bush Sr. and Clinton administrations for publicly available strong cryptography with keys escrowed by the government (NIST and the Treasury Dept.). Capstone included one or F-Secure VPN Plus Client v5.0 crack serial keygen tamper-proof computer chips for implementation (Clipper), a secret key encryption algorithm (Skipjack), digital signature algorithm (DSA), key exchange algorithm (KEA), and hash algorithm (SHA).
Challenge-Handshake Authentication Protocol (CHAP)An authentication scheme that allows one party to prove who they are to a second party by demonstrating knowledge of a shared secret without actually divulging that shared secret to a third party who might be listening. Described in RFC
Chips-Message Robust Authentication (CHIMERA)A scheme proposed for authenticating navigation data and the spreading code of civilian signals in the Global Positioning System (GPS). This is an anti-spoofing mechanism to protect the unencrypted civilian signals; GPS military signals are encrypted.
ClipperThe computer chip that would implement the Skipjack encryption scheme. The Clipper chip was to have had a deliberate backdoor so that material encrypted with this device would not be beyond the government's reach. Described inClipper was dead by See also EPIC's The Clipper Chip Web page.
Cryptography Research and Evaluation Committees (CRYPTEC)Similar in concept F-Secure VPN Plus Client v5.0 crack serial keygen the NIST AES process and NESSIE, CRYPTEC is the Japanese government's process to evaluate algorithms submitted for government and industry applications. CRYPTEX maintains a list of public key and secret key ciphers, hash functions, F-Secure VPN Plus Client v5.0 crack serial keygen, MACs, and other crypto algorithms approved for various applications in government environments.
Derived Unique Key Per F-Secure VPN Plus Client v5.0 crack serial keygen (DUKPT)A key management scheme used for debit and credit card verification with point-of-sale (POS) transaction systems, automated teller machines (ATMs), and other financial applications. In DUKPT, a unique key is derived for each transaction based upon a fixed, shared key in such a way that knowledge of one derived neat video fcpx crack mac Archives does not easily yield knowledge of other keys (including the fixed key). Therefore, if one of the derived keys is compromised, neither past nor subsequent transactions are endangered. DUKPT is specified in American National Standard (ANS) ANSI X (Retail Financial Services Symmetric Key Management Part 1: Using Symmetric Techniques) and can be purchased at the ANSI X Web page.
ECRYPT Stream Cipher Project (eSTREAM)The eSTREAM project came about as a result of the failure of the NESSIE project to produce a stream cipher that survived cryptanalysis. eSTREAM ran from to with the primary purpose of promoting the design of efficient and compact stream ciphers. As of Septemberthe eSTREAM suite contains seven sciphers.
Escrowed Encryption Standard (EES)Largely unused, a controversial crypto scheme employing the SKIPJACK secret key crypto algorithm and a Law Enforcement Access Field (LEAF) creation method. LEAF was one part of the key escrow system and allowed for decryption of ciphertext messages that had been intercepted by law enforcement agencies. Described more in FIPS PUB (archived; no longer in force).
Federal Information Processing Standards (FIPS)These computer security- and crypto-related FIPS PUBs are produced by the PhpStorm 2020.3.1 Crack Archives. National Institute of Standards and Technology (NIST) as standards for the U.S. Government. Current Federal Information Processing Standards (FIPS) related to crytography include:
FortezzaA PCMCIA card developed by NSA that implements the Capstone algorithms, intended for use with the Defense Messaging Service (DMS). Originally called Tessera.
GOSTGOST is a family of algorithms defined in the Russian cryptographic standards. Although most of the specifications are written in Russian, a series of RFCs describe some of the aspects so that the algorithms can be used effectively in Internet applications:
  • RFC Additional Cryptographic Algorithms for Use with GOSTGOST R F-Secure VPN Plus Client v5.0 crack serial keygen, GOST Rand GOST R Algorithms
  • RFC Using the GOSTGOST RGOST NTLite Crack Keygen Full Version Download Archivesand GOST R Algorithms with Cryptographic Message Syntax (CMS)
  • RFC Using the GOST RGOST Rand GOST R Algorithms with the Internet X Public Key Infrastructure Certificate and CRL Profile
  • RFC GOST Encryption, Decryption, F-Secure VPN Plus Client v5.0 crack serial keygen, and Message Authentication Code (MAC) Algorithms
  • RFC GOST R Hash Function Algorithm
  • RFC GOST R Digital Signature Algorithm (Updates RFC GOST R )
  • RFC GOST R Block Cipher "Kuznyechik"
  • RFC Guidelines on the Cryptographic Algorithms to Accompany the Usage of Standards GOST R and GOST R
  • RFC GOST R Block Cipher "Magma"
IP Security (IPsec)The IPsec protocol suite is used to provide privacy and authentication services at the IP layer. An overview of the protocol suite and F-Secure VPN Plus Client v5.0 crack serial keygen the documents comprising IPsec can be found in RFC Other documents include:
  • RFC IP security architecture.
  • RFC IP Authentication Header (AH), one of the two primary IPsec functions; AH provides connectionless integrity and data origin authentication for IP datagrams and protects against replay attacks.
  • RFC IP Encapsulating Security Payload (ESP), the other primary IPsec F-Secure VPN Plus Client v5.0 crack serial keygen ESP provides a variety of security services within IPsec.
  • RFC Extended Sequence Number (ESN) Addendum, allows for negotiation of a or bit sequence number, used to detect replay attacks.
  • RFC Cryptographic algorithm implementation requirements for ESP and AH.
  • RFC The Internet Key Exchange (IKE) protocol, version 2, providing for mutual authentication and establishing and maintaining security associations.
    • IKE v1 was described in three separate documents, RFC (application of ISAKMP to IPsec), RFC (ISAKMP, a framework for key management and security associations), and RFC (IKE, using part of Oakley and part of SKEME in conjunction with ISAKMP to obtain authenticated keying material for use with ISAKMP, and for other security associations such as AH and ESP). IKE v1 is obsoleted with the introduction of IKEv2.
  • RFC Cryptographic algorithms used with IKEv2.
  • RFC Crypto suites for IPsec, IKE, and IKEv2.
  • RFC The use of AES in CBC-MAC mode with IPsec ESP.
  • RFC The use of the Camellia cipher algorithm in IPsec.
  • RFC The Use of RSA/SHA-1 Signatures within Encapsulating Security Payload (ESP) and Authentication Header (AH).
  • RFC Describes AES-XCBC-PRF, a pseudo-random function derived from the AES for use with IKE.
  • RFC Describes use of the HMAC with MD5 algorithm for data origin authentication and integrity protection in both AH and ESP.
  • RFC Describes use of DES-CBC (DES in Cipher Block Chaining Mode) for confidentiality in ESP.
  • RFC Defines use of the NULL encryption algorithm (i.e., provides authentication and integrity without confidentiality) in ESP.
  • RFC Describes OAKLEY, F-Secure VPN Plus Client v5.0 crack serial keygen key determination and distribution protocol.
  • RFC Describes use of Cipher Block Chaining (CBC) mode cipher algorithms with ESP.
  • RFCs and Description of Photuris, a session-key management protocol for IPsec.

In addition, RFC describes Suite B Cryptographic Suites for IPsec and RFC describes the Suite B profile for IPsec.

IPsec was first proposed for use with IP version 6 (IPv6), but can also be employed with the current IP version, IPv4.

(See more detail about IPsec below in Section )

Internet Security Association and Key Management Protocol (ISAKMP/OAKLEY)ISAKMP/OAKLEY provide an infrastructure for Internet secure communications. ISAKMP, designed by the National Security Agency (NSA) and described in RFCis a framework for key management and security associations, independent of the key generation and cryptographic algorithms actually employed. The OAKLEY Key Determination Protocol, described in RFCis a key determination and distribution protocol using a variation of Diffie-Hellman.
KerberosA secret key encryption and authentication system, designed to authenticate requests for network resources within a user domain rather than to authenticate messages. Kerberos also uses a trusted third-party approach; a client communications with the Kerberos server to obtain "credentials" so that it may access services at the application server. Kerberos V4 used DES to generate keys and encrypt messages; Kerberos V5 uses DES and other schemes for key generation.

Microsoft added support for Kerberos V5 &#; with some proprietary extensions &#; in Windows Active Directory. There are many Kerberos articles posted at Microsoft's Knowledge Base, notably "Kerberos Explained."
Keyed-Hash Message Authentication Code (HMAC)A message authentication scheme based upon secret key cryptography and the secret key shared between two parties rather than public key methods. Described in FIPS PUB and RFC (See Section below for details on HMAC operation.)
Message Digest Cipher (MDC)Invented by Peter Gutman, MDC turns a one-way hash function into a block cipher.
MIME Object Security Services (MOSS)Designed as a successor to PEM to provide PEM-based security services to MIME messages. Described in RFC Never widely implemented and now defunct.
Mujahedeen SecretsA Windows GUI, PGP-like cryptosystem. Developed by supporters of Al-Qaeda, the program employs the five finalist AES algorithms, namely, MARS, RC6, Rijndael, Serpent, and Twofish. Also described in Inspire Magazine, Issue 1, pp. and Inspire Magazine, Issue 2, pp. Additional related information can also be found in "How Al-Qaeda Uses Encryption Post-Snowden (Part 2)."
New European Schemes for Signatures, Integrity and Encryption (NESSIE)NESSIE was an independent project meant to augment the work of NIST during the AES adoption process by putting out an open call for new cryptographic primitives. The NESSIE project ran from about While several new block ciper, PKC, MAC, and digital signature algorithms were found during the NESSIE process, no new stream cipher survived cryptanalysis. As a result, the ECRYPT Stream Cipher Project (eSTREAM) was created.
NSA Suite B CryptographyAn NSA standard for securing information at the SECRET level. Defines use of:
  • Advanced Encryption Standard (AES) with key sizes of and bits, per FIPS PUB for encryption
  • The Ephemeral Unified Model and the One-Pass Diffie Hellman (referred to as ECDH) using the curves with and bit prime moduli, per NIST Special Publication A for key exchange
  • Elliptic Curve Digital Signature Algorithm (ECDSA) using the curves with and bit prime moduli, per FIPS PUB for digital signatures
  • Secure Hash Algorithm (SHA) using and bits, per FIPS PUB for hashing

RFC describes Suite B Cryptographic Suites for Secure Shell (SSH) and RFC describes Suite B Cryptographic Suites for Secure IP (IPsec).

RFC reclassifies the RFCs related to the Suite B cryptographic algorithms as Historic, and it discusses the reasons for doing so.

Pretty Good Privacy (PGP)A family of cryptographic routines for e-mail, file, and disk encryption developed by Philip Zimmermann. PGP x uses RSA for key management and digital signatures, IDEA for message encryption, and MD5 for computing the message's hash value; more information can also be found in RFC PGP 5.x (formerly known as "PGP 3") uses Diffie-Hellman/DSS for key management and digital signatures; IDEA, CAST, F-Secure VPN Plus Client v5.0 crack serial keygen, or 3DES for F-Secure VPN Plus Client v5.0 crack serial keygen encryption; and MD5 or SHA for computing the message's hash value. OpenPGP, described in RFCis an open definition of security software based on PGP 5.x. The GNU F-Secure VPN Plus Client v5.0 crack serial keygen Guard (GPG) is a free software version of OpenPGP.

(See more detail about PGP below in Section )

Privacy Enhanced Mail (PEM)An IETF standard for secure electronic mail over the Internet, including provisions for encryption (DES), authentication, and key management (DES, F-Secure VPN Plus Client v5.0 crack serial keygen, RSA). Developed by the IETF but never widely used. Described in the following RFCs:
  • RFC Part I, Message Encryption and Authentication Procedures
  • RFC Part II, Certificate-Based Key Management
  • RFC Part III, Algorithms, Modes, and Identifiers
  • RFC Part IV, Key Certification and Related Services
Private Communication Technology (PCT)Developed by Microsoft for secure communication on the Internet. PCT supported Diffie-Hellman, Fortezza, and RSA for key establishment; DES, RC2, RC4, and triple-DES for encryption; and DSA and RSA message signatures. Never widely used; superceded by SSL and TLS.
Secure Electronic Transaction (SET)A communications protocol for securing credit card transactions, developed by MasterCard and VISA, in cooperation with IBM, Microsoft, RSA, and other companies. Merged F-Secure VPN Plus Client v5.0 crack serial keygen other protocols: Secure Electronic Payment Protocol (SEPP), an open specification for secure bank card transactions over the Internet developed by CyberCash, GTE, IBM, MasterCard, and Netscape; and Secure Transaction Technology (STT), a secure payment protocol developed by Microsoft and Visa International. Supports DES and RC4 for encryption, and RSA for signatures, key exchange, and public key encryption of bank card numbers. SET V is described in Book 1, Book 2, and Book 3. SET has been superceded by SSL and TLS.
Secure Hypertext Transfer Protocol (S-HTTP)An extension to HTTP to provide secure exchange of documents over the World Wide Web. Supported algorithms include RSA and Kerberos for key exchange, DES, IDEA, RC2, and Triple-DES for encryption. Described in RFC S-HTTP was never as widely used as HTTP over SSL (https).
Secure Multipurpose Internet Mail Extensions (S/MIME)An IETF secure e-mail scheme superceding PEM, F-Secure VPN Plus Client v5.0 crack serial keygen, and adding digital signature and encryption capability to Internet MIME messages. S/MIME Version is described in RFCs andand employs the Cryptographic Message Syntax described in RFCs and

(More detail about S/MIME can be found below in Section )
Secure Sockets Layer (SSL)Developed in by Netscape Communications to provide application-independent security and privacy over the Internet. F-Secure VPN Plus Client v5.0 crack serial keygen is designed so that protocols such as HTTP, FTP (File Transfer Protocol), and Telnet can operate over it transparently. SSL allows both server authentication (mandatory) and client authentication (optional). RSA is used during negotiation to exchange keys and identify the actual cryptographic algorithm (DES, IDEA, RC2, RC4, or 3DES) to use for the session. SSL also uses MD5 for message digests and X public key certificates. SSL was found to be breakable soon after the IETF announced formation of group to work on TLS and RFC specifically prohibits the use of SSL v by TLS clients. SSL version is described in RFC All versions of SSL are now deprecated in favor of TLS; TLS v is sometimes referred to as "SSL v"

(More detail about SSL can be found below in Section )
Server Gated Cryptography (SGC)Microsoft extension to SSL that provided strong encryption for online banking and other financial applications using RC2 (bit key), RC4 (bit key), DES (bit key), or 3DES (equivalent of bit key). Use of SGC required an Windows NT Server running Internet Information Server (IIS) with a valid SGC certificate. SGC was available in bit Windows versions of Internet Explorer (IE) ; support for Mac, Unix, and bit Windows versions of IE was planned, but never materialized, and SGC was made moot when browsers started to ship with bit encryption.
ShangMi (SM) Cipher SuitesA suite of authentication, encryption, and hash algorithms from the People's Republic of China.
  • SM2 Cryptography Algorithm: A public key crypto scheme based on elliptic curves. An overview of the specification, in Chinese, can be found in GM/T Additional specifications can be found in:
  • SM3 Cryptographic Hash Algorithm: A hash algorithm operating on bit blocks to produce a bit hash value. Described in GB/T
  • SM4 Block Cipher Algorithm: A Feistel F-Secure VPN Plus Client v5.0 crack serial keygen cipher algorithm with a block length and key length of bits, and 32 rounds. Described in GB/T
An application of the ShangMi Cipher Suites in TLS can be found in RFC
Signal ProtocolA protocol for providing end-to-end encryption for voice calls, video calls, F-Secure VPN Plus Client v5.0 crack serial keygen, and instant messaging (including group chats). Employing a combination of AES, ECC, and HMAC algorithms, it offers such features as confidentiality, integrity, authentication, forward/future secrecy, and message repudiation. Signal is particularly interesting because of its lineage and widespread use. The Signal Protocol's earliest versions were known as TextSecure, first developed by Open Whisper Systems in TextSecure itself was based on a protocol called Off-the-Record (OTR) Messaging, designed as an improvement over OpenPGP and S/MIME. TextSecure v2 () introduced a scheme called the Axolotl Ratchet for key exchange and added additional communication features. After subsequent iterations improving key management (and the renaming of the key exchange protocol to Double Ratchet), F-Secure VPN Plus Client v5.0 crack serial keygen, additional cryptographic primitives, and the addition of an encrypted voice calling application (RedPhone), TextSecure was renamed Signal Protocol in The F-Secure VPN Plus Client v5.0 crack serial keygen key exchange algorithm is at the heart of the power of this system. Most messaging apps employ the users' public and private keys; the weakness here is that if the phone falls into someone else's hands, all of the messages on the device &#; including deleted messages &#; can be decrypted. The Ratchet algorithm generates a set of so-called "temporary keys" for each user, based upon that user's public/private key pair. When two users exchange messages, the Signal protocol creates a secret key by combining the temporary and permanent pairs of public and private keys for both users. Each message is assigned its own secret key. Because the generation of the secret key requires access to both users' private keys, it exists only on their two devices. The Signal Protocol is/has been employed in:
  • WhatsApp (introduced )
  • G Data Software's Secure Chat (introduced ; service discontinued )
  • Google's Allo app (introduced ; NordVPN Crack 6.26.7.0 With License Key (Till 2022) in favor of Messages app, )
  • Facebook Messenger (introduced )
  • Skype's Private Conversations mode (introduced )
  • All of Google's Rich Communication Services (RCS) on Android systems (introduced )
A reasonably good writeup of the protocol can be found in "Demystifying the Signal Protocol for End-to-End Encryption (E2EE)" by Kozhukhovskaya, Mora, and Wong ().
Simple Authentication and Security Layer (SASL)A framework for providing authentication and data security services in connection-oriented protocols (a la TCP), described in F-Secure VPN Plus Client v5.0 crack serial keygen It provides a structured interface and allows new protocols to reuse existing authentication mechanisms and allows old protocols to make use of new mechanisms.

It has been common practice on the Internet to permit anonymous access to various services, employing a plain-text password using a user name of "anonymous" and a password of an email address or some other identifying information, F-Secure VPN Plus Client v5.0 crack serial keygen. New IETF protocols disallow plain-text logins. The Anonymous SASL Mechanism (RFC ) provides a method for anonymous logins within the SASL F-Secure VPN Plus Client v5.0 crack serial keygen Key-Management for Internet Protocol (SKIP)
Key management scheme for secure IP communication, specifically for IPsec, and designed by Aziz and Diffie. SKIP essentially defines a public key infrastructure for the Internet and even uses X certificates. Most public key cryptosystems assign keys on a per-session basis, which is inconvenient for the Internet since IP is connectionless. Instead, SKIP provides a basis for secure communication between any pair of Internet hosts. SKIP can employ DES, 3DES, IDEA, RC2, RC5, MD5, and SHA As it happened, SKIP was not adopted for IPsec; IKE was selected instead.
SM9Chinese Standard GM/T SM9 () is the Chinese national standard for Identity Based Cryptography. SM9 comprises three cryptographic algorithms, namely the Identity Based Digital Signature Algorithm, Identity Based Key Agreement Algorithm, and Identity Based Key Encapsulation Algorithm (allowing one party to securely send a symmetric key to another party). The SM9 scheme is also described in The SM9 Cryptographic Schemes (Z. Cheng).
TelegramTelegram, launched inis a cloud-based instant messaging and voice over IP (VoIP) service, with client app software available for all major computer and mobile device operating systems. Telegram allows users to exchange messages, photos, videos, etc., and supplies end-to-end encryption using a F-Secure VPN Plus Client v5.0 crack serial keygen called MTProto. stickers, audio and files of any type. MTProto employs bit AES, bit RSA, and Diffie-Hellman key exchange. There have been several contriversies with Telegram, not the least of which has to do with the nationality of the founders and the true location of the business, as well as some operation issues. From a cryptological viewpoint, however, one cautionary tale can be found in "On the CCA (in)security of MTProto" (Jakobsen & Orlandi, ), who describe some of the crypto weaknesses of the protocol; specifically, that "MTProto does not satisfy the definitions of authenticated encryption (AE) or indistinguishability under chosen-ciphertext attack (IND-CCA)" (p. 1).
Transmission Control Protocol (TCP) encryption (tcpcrypt)As ofF-Secure VPN Plus Client v5.0 crack serial keygen, the majority of Internet TCP traffic is not encrypted. The two primary reasons for this are (1) many legacy protocols have no mechanism with which to employ encryption (e.g., without a command such as STARTSSL, the protocol cannot invoke use of any encryption) and (2) many legacy applications cannot be upgraded, so no new encryption can be added. The response from the IETF's TCP Increased Security Working Group was to define a transparent way within the transport layer (i.e., TCP) with which to invoke encryption. The TCP Encryption Negotiation Option (TCP-ENO) addresses these two problems with an out-of-band, fully backward-compatible TCP option with which to negotiate use of LST Server - Lan Speed Test Server 1.3 crack serial keygen. TCP-ENO is described in RFC and tcpcrypt, an encryption protocol to protect TCP streams, is described in RFC
Transport Layer Security (TLS)TLS v is an IETF specification (RFC ) intended to replace SSL v TLS v employs Triple-DES (secret key cryptography), SHA (hash), Diffie-Hellman (key exchange), and DSS (digital signatures). TLS v was vulnerable to attack and updated by v (RFC ), which is now classified as an HISTORIC specification. TLS v was replaced by TLS v (RFC ) and, subsequently, by v (RFC ).

TLS is designed to operate over TCP. The IETF developed the Datagram Transport Layer Security (DTLS) protocol to operate over UDP. DTLS v is described in RFC

(See more detail about TLS below in Section )
TrueCryptOpen source, multi-platform cryptography software that can be used to encrypt a file, partition, or entire disk. One of TrueCrypt's more interesting features is that of plausible deniability with hidden volumes or hidden operating systems. The original Web site, storycall.us, suddenly went dark in May The current fork of TrueCrypt is VeraCrypt.

(See more F-Secure VPN Plus Client v5.0 crack serial keygen about TrueCrypt below in Section )
XITU-T recommendation for the format of certificates for the public key infrastructure. Certificates map (bind) a user identity to a public key. The IETF application of X certificates is documented in RFC An Internet X Public Key Infrastructure is further defined in RFC (Certificate Management Adobe After Effects CC 2021 Crack Full Setup Keys and RFC (Certificate Policy and Certification Practices Framework).

Password Protection

Nearly all modern multiuser computer and network operating systems employ passwords at the very least to protect and authenticate users accessing computer and/or network resources. But passwords are not typically kept on a host or server in plaintext, but are generally encrypted using some sort of hash scheme.

A) /etc/passwd file root:Jbw6BwE4XoUHoroot:/root:/bin/bash carol:FM5ikbQt1KCarol Monaghan:/home/carol:/bin/bash alex:LqAi7Mdyg/HcQAlex Insley:/home/alex:/bin/bash gary:FkJXupRyFqY4sGary Kessler:/home/gary:/bin/bash todd:edGqQUAaGv7gTodd Pritsky:/home/todd:/bin/bash josh:FiH0ONcjPut1gJoshua Kessler:/home/webroot:/bin/bash B.1) /etc/passwd file (with shadow passwords) root:xroot:/root:/bin/bash carol:xCarol Monaghan:/home/carol:/bin/bash alex:xAlex Insley:/home/alex:/bin/bash gary:xGary Kessler:/home/gary:/bin/bash todd:xTodd Pritsky:/home/todd:/bin/bash josh:xJoshua Kessler:/home/webroot:/bin/bash B.2) /etc/shadow file root:AGFw$1$P4u/uhLK$storycall.us35rlu65WlfCzq carol:kjHaN%35a8xMM8a/0kMl1?fwtLAM.K&kw alex:1$1KKmfTy0a7#storycall.us9a8H71lkwn/.hH22a gary:9ajlknknKJHjhnuypnAIJKL$storycall.us toddPOJ90uab6.k$klPqMt%alMlprWqu6$ josh:Awmqpsui*pjnsnJJK%aappaMpQo

FIGURE 8: Sample entries in Unix/Linux password files.

Unix/Linux, for example, uses a well-known hash via its crypt() function. Passwords are stored in the /etc/passwd file (Figure 8A); each record in the file contains the username, hashed password, user's individual and group numbers, user's name, home directory, and shell program; these fields are separated by colons (:). Note that each password is stored as a byte string. The first two characters are actually a salt, randomness added to each password so that if two users have the same password, they will still be encrypted differently; the salt, in fact, provides a means so that a single password might have different encryptions. The remaining 11 bytes are the password hash, calculated using DES.

As it happens, the /etc/passwd file is world-readable on Unix systems. This fact, coupled with the weak encryption of the passwords, resulted in the development of the shadow password system where passwords are kept in a separate, non-world-readable file used in conjunction with the normal password file. When shadow passwords are used, the password entry in /etc/passwd is replaced with a "*" or "x" (Figure 8B.1) and the MD5 hash of the passwords are stored in /etc/shadow along with some other account information (Figure 8B.2).

Windows NT uses a similar scheme to store passwords in the Security Access Manager (SAM) file. In the NT case, all passwords are hashed using the MD4 algorithm, resulting in a bit (byte) hash value (they are then obscured using an undocumented mathematical transformation that was a secret until distributed on the Internet). The password password, for example, might be stored as the hash value (in hexadecimal) b22d73c34bd4aa79c8b09f

Passwords are not saved in plaintext on computer systems precisely so they cannot be easily compromised. For similar reasons, we don't want passwords sent in plaintext across a network. But for remote logon applications, how does a client system identify itself or a user to the server? One mechanism, of course, is to send the password as a hash value and that, indeed, may be done. A weakness of that approach, however, F-Secure VPN Plus Client v5.0 crack serial keygen, is that an intruder can grab the password off of the network and use an off-line attack (such as a dictionary attack where an attacker takes every known word and encrypts it with the network's encryption algorithm, hoping eventually to find a match COREL DRAW X4 KEY GEN crack serial keygen a purloined password hash). In some situations, an attacker only has to copy the hashed password value and use it later on to gain unauthorized entry Sony Vegas Trial,ou 7.0 crack serial keygen ever learning the actual password.

An even stronger authentication method uses the password to modify a shared secret between the client and server, but never allows the password in any form to go across the network, F-Secure VPN Plus Client v5.0 crack serial keygen. This is the basis for the Challenge Handshake Authentication Protocol (CHAP), the remote logon process used by Windows NT.

As suggested above, Windows NT passwords are stored in a security file on a server as a byte hash value. In truth, Windows NT stores two hashes; a weak hash based upon the old LAN Manager (LanMan) scheme and the newer NT hash. When a user logs on to a server from a remote workstation, the user is identified by the username, sent across the network in plaintext (no worries here; it's not a secret anyway!). The server then generates a bit random number and sends it to the client (also in plaintext). This number is the challenge.

Using the LanMan scheme, the client system then encrypts the challenge using DES. Recall that DES employs a bit key, acts on a bit block of data, and produces a bit output. In this case, the bit data block is the random number. The client actually uses three different DES keys to encrypt the random number, producing three different bit outputs. The first key is the first seven bytes (56 bits) of the password's hash value, the second key is the next seven bytes in the password's hash, and the third key is the remaining two bytes of the password's hash concatenated with five zero-filled bytes. (So, for the example above, F-Secure VPN Plus Client v5.0 crack serial keygen, the three DES keys would be b22d73c34, bd4aa79c8b0, and 9f) Each key is applied to the random number resulting in three bit outputs, which comprise the response. Thus, the server's 8-byte challenge yields a byte response from the client and this is all that would F-Secure VPN Plus Client v5.0 crack serial keygen seen on the network. F-Secure VPN Plus Client v5.0 crack serial keygen server, for its part, does the same calculation to ensure that Umemaro 3D Semen Analysis Free Download values match.

There is, F-Secure VPN Plus Client v5.0 crack serial keygen, however, a significant weakness to this system. Specifically, the response is generated in such a way as to effectively reduce byte hash to three smaller hashes, of length seven, seven, and two, respectively. Thus, a password cracker has to break at most a 7-byte hash. One Windows NT vulnerability test program that I used in the past reported passwords that were "too short," defined as "less than 8 characters." When I asked how the program knew that passwords were too short, the software's salespeople suggested to me that the program broke the passwords to determine their length. This was, in fact, not the case at all; all Wondershare PDFelement Crack 8.2.9.924 software really had to do was to look at the last eight bytes of the Windows NT LanMan hash to see that the password was seven or fewer characters.

Consider the following example, showing the LanMan hash of two different short passwords (take a close look at the last 8 bytes):

AA: 89D42A44EAAAAD3BBEE
AAA: 1C3A2B6DAAAD3BBEE

Note that the NT hash provides no such clue:

AA: CFBE79C8FD99FE7AAD8
AAA: 6B6E0FB2EDBC73B5BFB77

It F-Secure VPN Plus Client v5.0 crack serial keygen worth noting that the discussion above describes the Microsoft version of CHAP, or MS-CHAP (MS-CHAPv2 is described in RFC ). MS-CHAP assumes that it is working with hashed values of the password as the key to encrypting the challenge, F-Secure VPN Plus Client v5.0 crack serial keygen. More traditional CHAP (RFC ) assumes that it is starting with passwords in plaintext. The relevance of this observation is that a CHAP client, for example, cannot be authenticated by an MS-CHAP server; both client and server must use the same CHAP version.

Diffie-Hellman Key Exchange

Diffie and Hellman introduced the concept of public key cryptography. The mathematical "trick" of Diffie-Hellman key exchange is that it is relatively easy to compute exponents compared to computing discrete logarithms. Diffie-Hellman allows two parties &#; the ubiquitous Alice and Bob &#; to generate a secret key; they need to exchange some information over an unsecure communications channel to perform the calculation but an eavesdropper cannot determine the shared secret key based upon this information.

Diffie-Hellman MindMaster 9.0.3 Crack FREE Download like this. Alice and Bob start by agreeing on a large prime number, N, F-Secure VPN Plus Client v5.0 crack serial keygen. They also have to choose some number G so that G<N.

There is actually another constraint on G, namely that it must be primitive with respect to N. Primitive is a definition that is a little beyond the scope of our discussion but basically G is primitive QuikQuak Pitchwheel v4.0 crack serial keygen N if the set of N-1 values of Gi mod N for i = (1,N-1) are all different. As an example, 2 is not primitive to 7 because the set of powers of 2 from 1 to 6, mod 7 (i.e., 21 mod 7, 22 mod 7,26 mod 7) = {2,4,1,2,4,1}. On the other hand, 3 is primitive to 7 because the set of powers of 3 from 1 to 6, mod 7 = {3,2,6,4,5,1}.

(The definition of primitive introduced a new term to some readers, F-Secure VPN Plus Client v5.0 crack serial keygen, namely mod. The phrase x mod y (and read as written!) means "take the remainder after dividing x by y." Thus, 1 mod 7 = 1, 9 mod 6 = 3, and 8 mod 8 = 0. Read more about the modulo function in the appendix.)

Anyway, either Alice or Bob selects N and G; they then tell the other party what the values are. Alice and Bob then work independently (Figure 9):

Alice

  1. Choose a large random number, XA < N. This is Alice's private key.
  2. Compute YA = GXA mod N. This is Alice's public key.
  3. Exchange public key with Bob.
  4. Compute KA = YBXA mod N
Bob

  1. Choose a large random number, XB < N. This is Bob's private key.
  2. Compute YB = GXB mod N. This is Bob's public key.
  3. Exchange public key with Alice.
  4. Compute KB = YAXB mod N
FIGURE 9: Diffie-Hellman key exchange model.

Note that XA and XB are kept secret while YA and YB are openly shared; these are the private and public keys, respectively. Based on their own private key and the public key learned from the PlayClaw torrent Archives party, Alice and Bob have computed their secret keys, KA and KB, respectively, which are equal to GXAXB mod N.

Perhaps a small example will help here. Although Alice and Bob will really choose large values for N and G, I will use small values for example only; let's use N=7 and G=3, as shown in Figure

Alice

  1. Choose private key; XA = 2
  2. Compute public key; YA = 32 mod 7 = 2
  3. Exchange public key with Bob
  4. KA = YBXA mod N = 62 mod 7 = 1
Bob

  1. Choose private key; XB = 3
  2. Compute public key; YB = 33 mod 7 = 6
  3. Exchange public key with Alice
  4. KB = YAXB mod N = 23 mod 7 = 1
FIGURE Diffie-Hellman key exchange example.

In this example, then, Alice and Bob will both find the secret key 1 which is, indeed, 36 mod 7 (i.e., GXAXB = 32x3). If an eavesdropper (Eve) was listening in on the information exchange between Alice and Bob, she would learn G, N, YA, and YB which is a lot of information but insufficient to compromise the key; as long as XA and XB remain unknown, K is safe. As stated above, calculating Y = GX is a lot easier than finding X = logG Y.


A short digression on modulo arithmetic. In the paragraph above, we noted that 36 mod 7 = 1. This can be confirmed, of course, by noting that:

36 = = *7 + 1

There is a nice property of modulo arithmetic, however, that makes this determination a little easier, namely: (a mod x)(b mod x) = (ab mod x). Therefore, one possible shortcut is to note that 36 = (33)(33). Therefore, 36 mod 7 = (33 mod 7)(33 mod 7) = (27 mod 7)(27 mod 7) = 6*6 mod 7 = 36 mod 7 = 1.


Diffie-Hellman can also be used to allow key sharing amongst multiple users. Note again that the Diffie-Hellman algorithm is used to generate secret keys, not to encrypt and decrypt messages.

RSA Public Key Cryptography

Unlike Diffie-Hellman, RSA can be used for key exchange as well as digital signatures and the encryption of small blocks of data. Today, RSA is primarily used to encrypt the session key used for secret key encryption (message integrity) or the message's hash value (digital signature). RSA's mathematical hardness comes from the ease in calculating large numbers and the difficulty in finding the prime factors of those large numbers. Although employed with numbers using hundreds of digits, the math behind RSA is relatively straight-forward.

To create an RSA public/private key pair, here are the basic steps:

  1. Choose two prime numbers, p and q. From these numbers you can calculate the modulus, n = pq.
  2. Select a third number, e, that is relatively prime to (i.e., it does not divide evenly into) the product (p-1)(q-1). The number e is the public exponent.
  3. Calculate an integer d from the quotient (ed-1)/[(p-1)(q-1)]. The number d is the private exponent.

The public key is the number pair (n,e). Although these values are publicly known, it is computationally infeasible to determine d from n and e if p and q are large enough.

To encrypt a message, M, with the public key, F-Secure VPN Plus Client v5.0 crack serial keygen, create the ciphertext, C, using the equation:

The receiver then decrypts the ciphertext with the private key using the equation:

F-Secure VPN Plus Client v5.0 crack serial keygen, this might look a bit complex and, indeed, the mathematics does take a lot of computer power given the large size of the numbers; since p and q may be digits (decimal) or more, d and e will be about the same size and n may be over digits. Nevertheless, a simple example may help. In this example, the values for p, q, e, and d are purposely chosen to be very small and the reader will see exactly how badly these values perform, but hopefully the algorithm will be adequately demonstrated:

  1. Select p=3 and q=5.
  2. The modulus n = pq =
  3. The value e must be relatively prime to (p-1)(q-1) = (2)(4) = 8. Select e=
  4. The value d must be chosen so that (ed-1)/[(p-1)(q-1)] is an integer. Thus, the value (11d-1)/[(2)(4)] = (11d-1)/8 must be an integer. Calculate one possible value, d=3.
  5. Let's suppose that we want to send a message &#; maybe a secret key &#; that has the numeric value of 7 (i.e., M=7). [More on this choice below.]
  6. The sender encrypts the message (M) using the public key value (e,n)=(11,15) and computes the ciphertext (C) with the formula C = 711 mod 15 =  mod 15 =
  7. The receiver decrypts the ciphertext using the private key value (d,n)=(3,15) and computes the plaintext with the formula M = 133 mod 15 =  mod 15 = 7.

I choose this trivial example because the value of n is so small (in particular, the value M cannot exceed n). But here is a more realistic example using larger d, e, and n values, as well as a more meaningful message; thanks to Barry Steyn for permission to use values from his How RSA Works With Examples page.

Let's say that we have chosen p and q so that we have the following value for n:





Let's also suppose that we have selected the public key, e, and private key, d, as follows:





Now suppose that our message (M) is the character string "attack at dawn" which has the numeric value (after converting the ASCII characters to a bit string and interpreting that bit string as a decimal number) of

The encryption phase uses the formula C = Me mod n, so C has the value:





The decryption phase uses the formula M = Cd mod n, so M has the value that matches our original plaintext:

This more realistic example gives just a clue as to how large the numbers are that are used in the real world implementations. RSA keylengths of and bits are considered to be pretty weak. The minimum suggested RSA key is bits; and bits are even better.

As an aside, Adam Back (storycall.us~adam/) wrote a two-line Perl script to implement RSA. It employs dc, an arbitrary precision arithmetic package that ships with most UNIX systems:

print pack"C*",split/\D+/,`echo "16iII*o\U@{$/=$z;[(pop,pop,unpack"H*",<> )]}\EsMsKsN0[lN*1lK[d2%Sa2/d0<X+d*lMLa^*lN%0]dsXx++lMlN/dsM0<J]dsJxp"

Comodo Internet F-Secure VPN Plus Client v5.0 crack serial keygen Internet Security (CIS) is developed and distributed by Comodo Group, a freemium Internet security suite that includes an antivirus program, personal firewall, sandbox, host-based intrusion prevention system (HIPS) and website filtering.

Version history[edit]

Release 5[edit]

In CIS cloud antivirus protection and spyware scanning capabilities were added. As it could not clean all the malware it found effectively, F-Secure VPN Plus Client v5.0 crack serial keygen, Comodo Cleaning Essentials was developed to supplement CIS.[4]

Host-based intrusion prevention system: Comodo's host-based intrusion prevention system (HIPS), named Defense+, is designed to provide protection against unknown malware. It is designed to restrict the actions of unknown applications, and restrict access to important files, folders, settings and the Windows Registry. Defense+ by default refuses any unknown program to install or execute except when specifically allowed by the user or when the file appears on Comodo's whitelist. In CIS a sandbox was added to Defense+ to isolate and run unknown applications.[5]

Release 6[edit]

CIS v6, released Februaryprovided a major revision of the user interface and significant new features such as a fully sandboxed desktop environment.[6]

Release 7[edit]

On 6 MarchComodo announced completion of beta testing for CIS v7. Release 7 became official in April This release includes a new virus monitoring tool called VirusScope and Web Filtering features that provide control over user access to web content.[citation needed]

Release 8[edit]

Became official on 3 November It includes enhanced auto-sandboxing features.[7]

Release 10[edit]

Became official on 22 December [8] It includes Secure Shopping, prevention on malware intercepting during online transactions.[9][10]

Release 11[edit]

Became official on 26 June It includes many stability and performance changes.

Release 12[edit]

Became official on F-Secure VPN Plus Client v5.0 crack serial keygen March It includes extra functionality in creating rules and full support for Windows 10 October update.[11]

Comodo Endpoint Security Manager (CESM)[edit]

Comodo Endpoint Security Manager (CESM) is a server product for centrally managing the security settings and security components of network endpoint computers.[12] CESM manages the distribution and updates of antivirus and firewall software.[13][14][15]

The antivirus and firewall software managed by CESM are versions of the same software used by the consumer versions of Comodo Internet Security[16][17][18]

Reception[edit]

Reviews[edit]

PC Magazine lead security analyst, Neil J. Rubenking, reviewed Comodo Firewall Pro and Comodo Internet Security on 3 NovemberF-Secure VPN Plus Client v5.0 crack serial keygen, giving out of 5 to the first and to the second. He praised the suite's firewall capabilities but criticized its antimalware capabilities.[19][20] On 28 MayRoboert Vamosi of PC World reviewed Comodo Internet Security and gave it a score of 1 out of 5, criticizing it for its "disappointing malware detection" based on AV-TEST result and "limited feature set".[21]

Three years and F-Secure VPN Plus Client v5.0 crack serial keygen version later, Comodo Antivirus results became significantly better. On 30 JanuaryRubenking reviewed Comodo Internet Security Pro (v), giving it 4 stars out of 5. He praised its support service and antimalware features but was panned for its "effectively off by default" firewall, Defense+ popups, lack of parental control, antispam, antiphishing, and privacy protection features, and finally, "Low ratings from independent labs".[22]

In a 9 January review, Techworld awarded Comodo Internet Security Pro 4 Jogos de Teste de Desempenho de Graça para Baixar 5 stars and concluded "Cloud-based scanning and behaviour analysis joins a suite of top-notch security tools, designed to keep your PC secure. Recommended."[23] Also on the same date, Mike Williams of storycall.us reviewed Comodo Internet Security Pro and concluded "The program remains too complex for total PC beginners, we suspect. The average user will appreciate its largely automatic operation, though, while experts enjoy the powerful tools and extreme configurability."[24]

On 7 FebruaryComodo Internet Security Complete v6 earned the PC Magazine Editor's Choice award. Reviewing the software again, Neil J. Reubenking gave it a score of 5 stars, commended its support service, F-Secure VPN Plus Client v5.0 crack serial keygen, VPN solution, Comodo Secure DNS service and value for price but criticized its behavior blocker and its poor anti-phishing capabilities. Reubenking concluded "The biggest win for Comodo Internet Security Complete isn't in features, F-Secure VPN Plus Client v5.0 crack serial keygen, but in support. The GeekBuddy service fixes any problem, security or otherwise, using remote assistance. A Virus-Free Guarantee reimburses you for damage if malware gets past Comodo; you can also get reimbursed for expenses related to identity theft. Add a GeekBuddy-powered tuneup tool and an unusually powerful backup utility and you've got a winner."[25]

Once again, PC Magazine lead security analyst, Neil J, F-Secure VPN Plus Client v5.0 crack serial keygen. Rubenking, reviewed Comodo Internet Security in with very poor performance.[26]

Independent test labs[edit]

AV-TEST, an anti-virus test lab based in Germany, tested Comodo, F-Secure VPN Plus Client v5.0 crack serial keygen. Products that surpass the industry standard (measured by the mean score of the participating products) are awarded a certificate. Comodo Internet Security participated in their tests sinceand for the first time in FebruaryComodo Internet Security Premium version obtained the AV-TEST certificate in the field of home products.[27]

On 18 JanuaryMatousec, an independent tester of security software, analyzed 38 security products for their proactive defense capabilities and ranked Comodo Internet Security Premium (v6) number one. Comodo Internet Security was tested on Windows 7 SP1 with Internet Explorer 9 and passed out of tests (92%).[28][29] It was also ranked number 1 in [30]

See also[edit]

References[edit]

External links[edit]

Источник: [storycall.us] dc`

DES, Breaking DES, and DES Variants

The Data Encryption Standard (DES) started life in the mids, adopted by the National Bureau of Standards (NBS) [now the National Institute of Standards and Technology (NIST)] as Federal Information Processing Standard 46 (FIPS PUB ) and by the American National Standards Institute (ANSI) as X

As mentioned earlier, DES uses the Data Encryption Algorithm (DEA), a secret key block-cipher employing a bit key operating on bit blocks. FIPS PUB 81 describes four modes of DES operation: Electronic Codebook (ECB), Cipher Block Chaining (CBC), Cipher Feedback (CFB), and Output Feedback (OFB). Despite all of these options, ECB is the most commonly deployed mode of operation.

NIST finally declared DES obsolete inand withdrew FIPS PUB74, and 81 (Federal Register, July 26,69(), ). Although other F-Secure VPN Plus Client v5.0 crack serial keygen ciphers have replaced DES, it is still interesting to see how DES encryption is performed; not only is it sort of neat, but DES was the first crypto scheme commonly seen in non-governmental applications and was the catalyst for modern "public" cryptography and the first public Feistel cipher. DES still remains in many products &#; and cryptography students and cryptographers will continue to study DES for years to come.

DES Operational Overview

DES uses a bit key. In fact, the bit key is divided into eight 7-bit blocks and an 8th odd parity bit is added to each block (i.e., a "0" or "1" is added to the block so that there are an odd number of 1 bits in each 8-bit block). By using the 8 parity bits for rudimentary error detection, F-Secure VPN Plus Client v5.0 crack serial keygen, a DES key is actually 64 bits in length for computational purposes although it only has 56 bits worth of randomness, or entropy (See Section A.3 for a brief discussion of entropy and information theory).

FIGURE DES enciphering algorithm.

DES F-Secure VPN Plus Client v5.0 crack serial keygen acts on bit blocks of the plaintext, invoking 16 rounds of permutations, swaps, and substitutes, as shown in Figure The standard includes tables describing all of the selection, permutation, and expansion operations mentioned below; these aspects of the algorithm are not secrets. The basic DES steps are:

  1. The bit block to be encrypted undergoes an initial permutation (IP), where each bit is moved to a new bit position; e.g., the 1st, 2nd, and 3rd bits are moved to the 58th, 50th, and 42nd position, respectively.

  2. The bit permuted input is divided into two bit blocks, called left and right, respectively. The initial values of the left and right blocks are denoted L0 and R0.

  3. There are then 16 rounds of operation on the L and R blocks. During each iteration (where n ranges from 1 to 16), the following formulae apply:

      Ln = Rn-1
      Rn = Ln-1 ⊕ f(Rn-1,Kn)

    At any given step in the process, then, the new L block value is merely taken from the prior R block value. The new R block is calculated by taking the bit-by-bit exclusive-OR (XOR) of the prior L block with the results of applying the DES cipher function, f, to the prior R block and Kn. (Kn is a bit value derived from the bit DES key. Each round uses a different 48 bits according to the standard's Key Schedule algorithm.)

    The cipher function, f, combines the bit R block value and the bit subkey in the following way. First, the 32 bits in the R block are expanded to 48 bits by an expansion function (E); the extra 16 bits are found by repeating the bits in 16 predefined positions. The bit expanded R-block is then ORed with the bit subkey. The result is a bit value that is then divided into eight 6-bit blocks. These are fed as input into 8 selection (S) boxes, denoted S1,S8. Each 6-bit input yields a 4-bit output using a table lookup based on the 64 possible inputs; this results in a bit output from the S-box. The 32 bits are then rearranged by a permutation function (P), producing the results from the cipher function.

  4. The results from the final DES round &#; i.e., L16 and R16 &#; are recombined into a bit value and fed into an inverse initial permutation (IP-1). At this step, the bits are rearranged into their original positions, so that the 58th, 50th, and 42nd bits, for example, are moved back into the 1st, 2nd, and 3rd positions, respectively. The output from IP-1 is the bit ciphertext block.

Consider this example using DES in CBC mode with the following bit key and input:

    Key: = 0xDB6C1A

    Input character string (ASCII/IA5): +
    Input string (hex): 0x2BD

    Output string (hex): 0xCBB2E9FD3AD90DE2B92C6BBB6CAC43E1AFA6
    Output character string (BASE64): mBLLYgsun9OtkN4rksa7tsUnU6xD4a+m

Observe that we start with a byte input message. DES acts on eight bytes at a time, so this message is padded to 24 bytes and provides three "inputs" to the cipher algorithm (we don't see the padding here; it is appended by the DES code). Since we have three input blocks, we get 24 bytes of output from the three bit (eight byte) output blocks.

If you want to test this, a really good free, online DES calculator hosted by the Information Security Group at University College London. An excellent step-by-step example of DES can also be found at J. Orlin Grabbe's The DES Algorithm Illustrated page.


NOTE: You'll notice that the output above is shown in BASE BASE64 is a character alphabet &#; i.e., a six-bit character code composed of upper- and lower-case letters, the digitsF-Secure VPN Plus Client v5.0 crack serial keygen, and a few punctuation characters &#; that is commonly used as a way to display binary data. A byte has eight bits, or values, but not all ASCII characters are defined and/or printable. BASE64, simply, takes a binary string (or file), divides it into six-bit blocks, and translates each block into a printable character. More information about BASE64 can be found at my BASE64 Alphabet page or at Wikipedia.

Breaking DES

The mainstream cryptographic community has long held that DES's bit key was too short to withstand a brute-force attack from modern computers. Remember Moore's Law: computer power doubles every 18 months. Given that increase in power, a key that could withstand a brute-force guessing attack in could hardly be expected to withstand the same attack a quarter century later.

DES is even more vulnerable to a brute-force attack because it is often used to encrypt words, meaning that the entropy of the bit block is, effectively, greatly reduced. That is, if we are encrypting random bit streams, then a given byte might contain any one of 28 () possible values and the entire bit block has 264, or about quintillion, possible values. If we are encrypting words, however, we are most likely to find a limited set of bit patterns; perhaps 70 F-Secure VPN Plus Client v5.0 crack serial keygen so if we account for upper and lower case letters, the numbers, space, and some punctuation. This means that only about &#; of the bit combinations of a given byte are likely to occur.

Despite this criticism, the U.S. government insisted throughout the mids that bit DES was secure and virtually unbreakable if appropriate precautions were taken. In response, RSA Laboratories sponsored a series of cryptographic challenges to prove that DES was no longer appropriate for use.

DES Challenge I was launched in March It was completed in 84 days by R. Verser in a collaborative effort using thousands of computers on the Internet.

The first DES Challenge II lasted 40 days in early This problem was solved by storycall.us, a worldwide distributed computing network using the spare CPU cycles of 4D Write 2.1 crack serial keygen around the Internet (participants in storycall.us's activities load a client program that runs in the background, conceptually similar to the SETI @Home "Search for Extraterrestrial Intelligence" project). The storycall.us systems were checking 28 billion keys per second by the end of the project.

The second DES Challenge II lasted less than 3 days. On July 17,the Electronic Frontier Foundation (EFF) announced the construction of F-Secure VPN Plus Client v5.0 crack serial keygen that could brute-force a DES key in an average of days. Called Deep Crack, the device could check 90 billion keys per second and cost only about $, including design (it was erroneously and widely reported that subsequent devices could be built for as little as $50,). Since the design is scalable, this suggests that an organization could build a DES cracker that could break bit keys in an average of a day for as little as $1, Information about the hardware design and all software can be obtained from the EFF.

The DES Challenge III, launched in Januarywas broken is less than a day by the combined efforts of Deep Crack and storycall.us This is widely considered to have been the final nail in DES's coffin.

The Deep Crack algorithm is actually quite interesting. The general approach that the DES Cracker Project took was not to break the algorithm mathematically but instead to launch a brute-force attack by guessing every possible key. A bit key yields 256, or about 72 quadrillion, possible values. So the DES cracker team looked for any shortcuts they could find! First, they assumed that some recognizable plaintext would appear in the decrypted string even though they didn't have a specific known plaintext block. They then applied all 256 possible key values to the bit block (I don't mean to make this sound simple!). The system checked to see if the decrypted value of the block was "interesting," which they defined as bytes containing one of the alphanumeric characters, space, or some punctuation. Since the likelihood of a single byte being "interesting" is about &#;, then the likelihood of the entire 8-byte stream being "interesting" is about &#;8, or 1/ (&#;16). This dropped the number of possible keys that might yield positive results to about 240, or about a trillion.

They then made the assumption that an "interesting" 8-byte block would be followed by another "interesting" block. So, if the first block of ciphertext decrypted to something interesting, they decrypted the next block; otherwise, they abandoned this key. Only if the second block was also "interesting" did they examine the key closer. Looking for 16 consecutive bytes that were "interesting" meant that only 224, or 16 million, keys needed to be examined further. This further examination was primarily to see if the text made any sense. Note that possible "interesting" blocks might be 1hJ5&aB7 or DEPOSITS; the latter is more likely to produce a better result. And even a slow laptop today can search through lists of only a few million items in a relatively short period of time. (Interested readers are urged to read Cracking DES and EFF's Cracking DES page.)

PDF-XChange Viewer 2.5.199 crack serial keygen is well beyond the scope of this paper to discuss other forms of breaking DES and other codes. Nevertheless, it is worth mentioning a couple of forms of cryptanalysis that have been shown to be effective against DES. Differential cryptanalysis, invented in by E. Biham and A. Shamir (of RSA fame), is a chosen-plaintext attack. By selecting pairs of plaintext with particular differences, the cryptanalyst examines the differences in the resultant ciphertext pairs. Linear plaintext, invented by M. Matsui, uses a linear approximation to analyze the actions of a block cipher (including DES). Both of these attacks can be more efficient than brute force.

DES Variants

Once DES was "officially" broken, several variants appeared. But none of them came overnight; work at hardening DES had already been underway. In the early s, there was a proposal to increase the security of DES by effectively increasing the key length by using multiple keys with multiple passes. But for this scheme to work, it had to first be shown that the DES function is not a group, as defined in mathematics. If DES was a group, then we could show that for two DES keys, X1 and X2, applied to some plaintext (P), we can find a single equivalent key, X3, that would provide the same result; i.e.,

EX2(EX1(P)) = EX3(P)

where EX(P) represents DES encryption of some plaintext P using DES key X. If DES were a group, it wouldn't matter how many keys and passes we applied to some plaintext; we could always find a single bit key that would provide the same result.

Источник: [storycall.us]

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This license is commonly used for video games and Wondershare Dr Fone 11.4.1 Crack [Latest] allows users to download and play the game for free. Basically, a product is offered Free to Play (Freemium) and the user can decide if he wants to pay the money (Premium) for additional features, services, virtual or physical goods that expand the functionality of the game, F-Secure VPN Plus Client v5.0 crack serial keygen. In some cases, ads may be show to the users.

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