The Secure Hash Algorithms are a family of
cryptographic hash functions published by the
National Institute of Standards and Technology (NIST) as a
U.S. Federal Information Processing Standard (FIPS), including:
*
SHA-0: A
retronym applied to the original version of the 160-bit hash function published in 1993 under the name "SHA". It was withdrawn shortly after publication due to an undisclosed "significant flaw" and replaced by the slightly revised version SHA-1.
*
SHA-1: A 160-bit hash function which resembles the earlier
MD5 algorithm. This was designed by the
National Security Agency (NSA) to be part of the
Digital Signature Algorithm. Cryptographic weaknesses were discovered in SHA-1, and the standard was no longer approved for most cryptographic uses after 2010.
*
SHA-2: A family of two similar hash functions, with different block sizes, known as ''SHA-256'' and ''SHA-512''. They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words. There are also truncated versions of each standard, known as ''SHA-224'', ''SHA-384'', ''SHA-512/224'' and ''SHA-512/256''. These were also designed by the NSA.
*
SHA-3: A hash function formerly called ''
Keccak'', chosen in 2012 after a public competition among non-NSA designers. It supports the same hash lengths as SHA-2, and its internal structure differs significantly from the rest of the SHA family.
The corresponding standards are
FIPS PUB 180 (original SHA), FIPS PUB 180-1 (SHA-1), FIPS PUB 180-2 (SHA-1, SHA-256, SHA-384, and SHA-512). NIST has updated Draft FIPS Publication 202, SHA-3 Standard separate from the Secure Hash Standard (SHS).
Comparison of SHA functions
In the table below, ''internal state'' means the "internal hash sum" after each compression of a data block.
Validation
All SHA-family algorithms, as FIPS-approved security functions, are subject to official validation by the CMVP (Cryptographic Module Validation Program), a joint program run by the American
National Institute of Standards and Technology (NIST) and the Canadian
Communications Security Establishment (CSE).
References
{{Cryptography hash
Cryptography