# 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 It was withdrawn shortly after publication due to an undisclosed "significant flaw" and replaced by the slightly revised version SHA-1.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-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.
Comparison of SHA functions viewtalkedit :
| Algorithm and variant | Algorithm and variant | Output size (bits) | Internal state size (bits) | Block size (bits) | Rounds | Operations | Security against collision attacks (bits) | Security against length extension attacks (bits) | Performance on Skylake (median cpb) | Performance on Skylake (median cpb) | First published |
| Algorithm and variant | Algorithm and variant | Output size (bits) | Internal state size (bits) | Block size (bits) | Rounds | Operations | Security against collision attacks (bits) | Security against length extension attacks (bits) | Long messages | 8 bytes | First published |
| MD5 (as reference) | MD5 (as reference) | 128 | 128 (4 × 32) | 512 | 4 (16 operations in each round) | And, Xor, Or, Rot, Add (mod 2$^{32}$) | ≤ 18 (collisions found) | 0 | 4.99 | 55.00 | 1992 |
| SHA-0 | SHA-0 | 160 | 160 (5 × 32) | 512 | 80 | And, Xor, Or, Rot, Add (mod 2$^{32}$) | < 34 (collisions found) | 0 | ≈ SHA-1 | ≈ SHA-1 | 1993 |
| SHA-1 | SHA-1 | 160 | 160 (5 × 32) | 512 | 80 | And, Xor, Or, Rot, Add (mod 2$^{32}$) | < 63 (collisions found) | 0 | 3.47 | 52.00 | 1995 |
| SHA-2 | SHA-224 SHA-256 | 224 256 | 256 (8 × 32) | 512 | 64 | And, Xor, Or, Rot, Shr, Add (mod 2$^{32}$) | 112 128 | 32 0 | 7.62 7.63 | 84.50 85.25 | 2004 2001 |
| SHA-2 | SHA-384 | 384 | 512 (8 × 64) | 1024 | 80 | And, Xor, Or, Rot, Shr, Add (mod 2$^{64}$) | 192 | 128 | 5.12 | 135.75 | 2001 |
| SHA-2 | SHA-512 | 512 | 512 (8 × 64) | 1024 | 80 | And, Xor, Or, Rot, Shr, Add (mod 2$^{64}$) | 256 | 0 | 5.06 | 135.50 | 2001 |
| SHA-2 | SHA-512/224 SHA-512/256 | 224 256 | 512 (8 × 64) | 1024 | 80 | And, Xor, Or, Rot, Shr, Add (mod 2$^{64}$) | 112 128 | 288 256 | ≈ SHA-384 | ≈ SHA-384 | 2012 |
| SHA-3 | SHA3-224 SHA3-256 SHA3-384 SHA3-512 | 224 256 384 512 | 1600 (5 × 5 × 64) | 1152 1088 832 576 | 24 | And, Xor, Rot, Not | 112 128 192 256 | 448 512 768 1024 | 8.12 8.59 11.06 15.88 | 154.25 155.50 164.00 164.00 | 2015 |
| SHA-3 | SHAKE128 SHAKE256 | d (arbitrary) d (arbitrary) | 1600 (5 × 5 × 64) | 1344 1088 | 24 | And, Xor, Rot, Not | min(d/2, 128) min(d/2, 256) | 256 512 | 7.08 8.59 | 155.25 155.50 | 2015 |

## 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).