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In cryptography, an HMAC is a specific type of message authentication code (MAC) involving a cryptographic hash function and a secret cryptographic key. As with any MAC, it may be used to simultaneously verify both the data integrity and authenticity of a message. An HMAC is a type of keyed hash function that can also be used in a key derivation scheme or a key stretching scheme.
The MD5 message-digest algorithm is a widely used hash function producing a 128-bit hash value. MD5 was designed by Ronald Rivest in 1991 to replace an earlier hash function MD4, and was specified in 1992 as RFC 1321.
In cryptography, SHA-1 is a hash function which takes an input and produces a 160-bit (20-byte) hash value known as a message digest – typically rendered as 40 hexadecimal digits. It was designed by the United States National Security Agency, and is a U.S. Federal Information Processing Standard. The algorithm has been cryptographically broken but is still widely used.
A cryptographic hash function (CHF) is a hash algorithm that has special properties desirable for a cryptographic application:
There are a number of standards related to cryptography. Standard algorithms and protocols provide a focus for study; standards for popular applications attract a large amount of cryptanalysis.
In cryptography, nothing-up-my-sleeve numbers are any numbers which, by their construction, are above suspicion of hidden properties. They are used in creating cryptographic functions such as hashes and ciphers. These algorithms often need randomized constants for mixing or initialization purposes. The cryptographer may wish to pick these values in a way that demonstrates the constants were not selected for a nefarious purpose, for example, to create a backdoor to the algorithm. These fears can be allayed by using numbers created in a way that leaves little room for adjustment. An example would be the use of initial digits from the number π as the constants. Using digits of π millions of places after the decimal point would not be considered trustworthy because the algorithm designer might have selected that starting point because it created a secret weakness the designer could later exploit.
Digest access authentication is one of the agreed-upon methods a web server can use to negotiate credentials, such as username or password, with a user's web browser. This can be used to confirm the identity of a user before sending sensitive information, such as online banking transaction history. It applies a hash function to the username and password before sending them over the network. In contrast, basic access authentication uses the easily reversible Base64 encoding instead of hashing, making it non-secure unless used in conjunction with TLS.
NSA Suite B Cryptography was a set of cryptographic algorithms promulgated by the National Security Agency as part of its Cryptographic Modernization Program. It was to serve as an interoperable cryptographic base for both unclassified information and most classified information.
SHA-2 is a set of cryptographic hash functions designed by the United States National Security Agency (NSA) and first published in 2001. They are built using the Merkle–Damgård construction, from a one-way compression function itself built using the Davies–Meyer structure from a specialized block cipher.
FORK-256 is a hash algorithm designed in response to security issues discovered in the earlier SHA-1 and MD5 algorithms. After substantial cryptanalysis, the algorithm is considered broken.
Panama is a cryptographic primitive which can be used both as a hash function and a stream cipher, but its hash function mode of operation has been broken and is not suitable for cryptographic use. Based on StepRightUp, it was designed by Joan Daemen and Craig Clapp and presented in the paper Fast Hashing and Stream Encryption with PANAMA on the Fast Software Encryption (FSE) conference 1998. The cipher has influenced several other designs, for example MUGI and SHA-3.
Skein is a cryptographic hash function and one of five finalists in the NIST hash function competition. Entered as a candidate to become the SHA-3 standard, the successor of SHA-1 and SHA-2, it ultimately lost to NIST hash candidate Keccak.
The NIST hash function competition was an open competition held by the US National Institute of Standards and Technology (NIST) to develop a new hash function called SHA-3 to complement the older SHA-1 and SHA-2. The competition was formally announced in the Federal Register on November 2, 2007. "NIST is initiating an effort to develop one or more additional hash algorithms through a public competition, similar to the development process for the Advanced Encryption Standard (AES)." The competition ended on October 2, 2012, when NIST announced that Keccak would be the new SHA-3 hash algorithm.
SHA-3 is the latest member of the Secure Hash Algorithm family of standards, released by NIST on August 5, 2015. Although part of the same series of standards, SHA-3 is internally different from the MD5-like structure of SHA-1 and SHA-2.
The following tables compare general and technical information for a number of cryptographic hash functions. See the individual functions' articles for further information. This article is not all-inclusive or necessarily up-to-date. An overview of hash function security/cryptanalysis can be found at hash function security summary.
The following outline is provided as an overview of and topical guide to cryptography:
BLAKE is a cryptographic hash function based on Daniel J. Bernstein's ChaCha stream cipher, but a permuted copy of the input block, XORed with round constants, is added before each ChaCha round. Like SHA-2, there are two variants differing in the word size. ChaCha operates on a 4×4 array of words. BLAKE repeatedly combines an 8-word hash value with 16 message words, truncating the ChaCha result to obtain the next hash value. BLAKE-256 and BLAKE-224 use 32-bit words and produce digest sizes of 256 bits and 224 bits, respectively, while BLAKE-512 and BLAKE-384 use 64-bit words and produce digest sizes of 512 bits and 384 bits, respectively.
In cryptography and computer security, a length extension attack is a type of attack where an attacker can use Hash(message1) and the length of message1 to calculate Hash(message1 ‖ message2) for an attacker-controlled message2, without needing to know the content of message1. This is problematic when the hash is used as a message authentication code with construction Hash(secret ‖ message), and message and the length of secret is known, because an attacker can include extra information at the end of the message and produce a valid hash without knowing the secret. Algorithms like MD5, SHA-1 and most of SHA-2 that are based on the Merkle–Damgård construction are susceptible to this kind of attack. Truncated versions of SHA-2, including SHA-384 and SHA-512/256 are not susceptible, nor is the SHA-3 algorithm. HMAC also uses a different construction and so is not vulnerable to length extension attacks.
In cryptography, security level is a measure of the strength that a cryptographic primitive — such as a cipher or hash function — achieves. Security level is usually expressed as a number of "bits of security", where n-bit security means that the attacker would have to perform 2n operations to break it, but other methods have been proposed that more closely model the costs for an attacker. This allows for convenient comparison between algorithms and is useful when combining multiple primitives in a hybrid cryptosystem, so there is no clear weakest link. For example, AES-128 is designed to offer a 128-bit security level, which is considered roughly equivalent to a RSA using 3072-bit key.
Dr. ir. Marc Stevens is a cryptology researcher most known for his work on cryptographic hash collisions and for the creation of the chosen-prefix hash collision tool HashClash as part of his master's degree thesis. He first gained international attention for his work with Alexander Sotirov, Jacob Appelbaum, Arjen Lenstra, David Molnar, Dag Arne Osvik, and Benne de Weger in creating a rogue SSL certificate which was presented in 2008 during the 25th annual Chaos Communication Congress warning of the dangers of using the MD5 hash function in issuing SSL certificates. Several years later in 2012, according to Microsoft, the authors of the Flame malware used similar methodology to that which the researchers warned of by initiating an MD5 collision to forge a Windows code-signing certificate. Marc was most recently awarded the Google Security Privacy and Anti-abuse applied award. Google selected Stevens for this award in recognition of his work in Cryptanalysis, in particular related to the SHA-1 hash function.
References
- ↑ "Measurements table". bench.cr.yp.to.
- ↑ Tao, Xie; Liu, Fanbao; Feng, Dengguo (2013). Fast Collision Attack on MD5 (PDF). Cryptology ePrint Archive (Technical report). IACR.
- ↑ Stevens, Marc; Bursztein, Elie; Karpman, Pierre; Albertini, Ange; Markov, Yarik. The first collision for full SHA-1 (PDF) (Technical report). Google Research.
- Marc Stevens; Elie Bursztein; Pierre Karpman; Ange Albertini; Yarik Markov; Alex Petit Bianco; Clement Baisse (February 23, 2017). "Announcing the first SHA1 collision". Google Security Blog.
- ↑ Without truncation, the full internal state of the hash function is known, regardless of collision resistance. If the output is truncated, the removed part of the state must be searched for and found before the hash function can be resumed, allowing the attack to proceed.
- ↑ "The Keccak sponge function family" . Retrieved 2016-01-27.