Secure Hash Algorithm

The Secure Hash Algorithm is 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 It was withdrawn shortly after publication due to an undisclosed "significant flaw" and replaced by the slightly revised version SHA-1.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

Algorithm and variant		Output size (bits)	Internal state size (bits)	Block size (bits)	Max message size (bits)	Rounds	Operations	Security (bits)	Example performance[1] (MiB/s)
MD5 (as reference)		128	128 (4 × 32)	512	2^64 − 1	64	And, Xor, Rot, Add (mod 2^32), Or	<64 (collisions found)	335
SHA-0		160	160 (5 × 32)	512	2^64 − 1	80	And, Xor, Rot, Add (mod 2^32), Or	<80 (collisions found)	-
SHA-1		160	160 (5 × 32)	512	2^64 − 1	80		<80 (theoretical attack[3])	192
SHA-2	SHA-224 SHA-256	224 256	256 (8 × 32)	512	2^64 − 1	64	And, Xor, Rot, Add (mod 2^32), Or, Shr	112 128	139
	SHA-384 SHA-512 SHA-512/224 SHA-512/256	384 512 224 256	512 (8 × 64)	1024	2^128 − 1	80	And, Xor, Rot, Add (mod 2^64), Or, Shr	192 256 112 128	154
SHA-3	SHA3-224 SHA3-256 SHA3-384 SHA3-512	224 256 384 512	1600 (5 × 5 × 64)	1152 1088 832 576	Unlimited[4]	24[5]	And, Xor, Rot, Not	112 128 192 256	-
	SHAKE128 SHAKE256	d (arbitrary) d (arbitrary)		1344 1088				min(d/2, 128) min(d/2, 256)	-

References

1. Found on an AMD Opteron 8354 2.2 GHz processor running 64-bit Linux^[2]
2. "Crypto++ 5.6.0 Benchmarks". Retrieved 2013-06-13.
3. "The SHAppening: freestart collisions for SHA-1". Retrieved 2015-11-05.
4. "The Sponge Functions Corner". Retrieved 2016-01-27.
5. "The Keccak sponge function family". Retrieved 2016-01-27.