Secure Hash Algorithms

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 It was withdrawn shortly after publication due to an undisclosed "significant flaw" and replaced by the slightly revised version SHA-1.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-byte words where SHA-512 uses 64-byte 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.

Comparison of SHA functions
Algorithm and variant Output size
(bits)
Internal state size
(bits)
Block size
(bits)
Rounds Operations Security (in bits) against collision attacks Capacity
against length extension attacks
Performance on Skylake (median cpb)[1] First published
long messages8 bytes
MD5 (as reference)128128
(4 × 32)
51264And, Xor, Rot, Add (mod 232), Or≤18
(collisions found)[2]
04.9955.001992
SHA-0160160
(5 × 32)
51280And, Xor, Rot, Add (mod 232), Or<34
(collisions found)
0≈ SHA-1≈ SHA-11993
SHA-1<63
(collisions found)[3]
3.4752.001995
SHA-2SHA-224
SHA-256
224
256
256
(8 × 32)
51264And, Xor, Rot, Add (mod 232), Or, Shr112
128
32
0
7.62
7.63
84.50
85.25
2004
2001
SHA-384
SHA-512
384
512
512
(8 × 64)
102480And, Xor, Rot, Add (mod 264), Or, Shr192
256
128 ( 384)
0[4]
5.12
5.06
135.75
135.50
2001
SHA-512/224
SHA-512/256
224
256
112
128
288
256
≈ SHA-384≈ SHA-3842012
SHA-3SHA3-224
SHA3-256
SHA3-384
SHA3-512
224
256
384
512
1600
(5 × 5 × 64)
1152
1088
832
576
24[5]And, Xor, Rot, Not112
128
192
256
448
512
768
1024
8.12
8.59
11.06
15.88
154.25
155.50
164.00
164.00
2015
SHAKE128
SHAKE256
d (arbitrary)
d (arbitrary)
1344
1088
min(d/2, 128)
min(d/2, 256)
256
512
7.08
8.59
155.25
155.50

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

  1. "Measurements table". bench.cr.yp.to.
  2. Tao, Xie; Liu, Fanbao; Feng, Dengguo (2013). Fast Collision Attack on MD5 (PDF). Cryptology ePrint Archive (Technical report). IACR.
  3. Stevens, Marc; Bursztein, Elie; Karpman, Pierre; Albertini, Ange; Markov, Yarik. The first collision for full SHA-1 (PDF) (Technical report). Google Research. Lay summary Google Security Blog (February 23, 2017).
  4. 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.
  5. "The Keccak sponge function family". Retrieved 2016-01-27.
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