SHA-2 (Secure Hash Algorithm 2) is a set of

cryptographic hash function A cryptographic hash function (CHF) is a hash algorithm (a map of an arbitrary binary string to a binary string with fixed size of n bits) that has special properties desirable for cryptography: * the probability of a particular n-bit output re ...

s designed by the United States

National Security Agency The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collect ...

(NSA) and first published in 2001. They are built using the

Merkle–Damgård construction In cryptography, the Merkle–Damgård construction or Merkle–Damgård hash function is a method of building collision-resistant cryptographic hash functions from collision-resistant one-way compression functions. Goldwasser, S. and Bellare, M ...

, from a

one-way compression function In cryptography, a one-way compression function is a function that transforms two fixed-length inputs into a fixed-length output. The transformation is "one-way", meaning that it is difficult given a particular output to compute inputs which compre ...

itself built using the Davies–Meyer structure from a specialized block cipher. SHA-2 includes significant changes from its predecessor,

SHA-1 In cryptography, SHA-1 (Secure Hash Algorithm 1) is a cryptographically broken but still widely used hash function which takes an input and produces a 160-bit (20- byte) hash value known as a message digest – typically rendered as 40 hexadec ...

. The SHA-2 family consists of six hash functions with digests (hash values) that are 224, 256, 384 or 512 bits: SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, SHA-512/256. SHA-256 and SHA-512 are novel hash functions computed with eight 32-bit and 64-bit words, respectively. They use different shift amounts and additive constants, but their structures are otherwise virtually identical, differing only in the number of rounds. SHA-224 and SHA-384 are truncated versions of SHA-256 and SHA-512 respectively, computed with different initial values. SHA-512/224 and SHA-512/256 are also truncated versions of SHA-512, but the initial values are generated using the method described in

Federal Information Processing Standards The Federal Information Processing Standards (FIPS) of the United States are a set of publicly announced standards that the National Institute of Standards and Technology (NIST) has developed for use in computer systems of non-military, America ...

(FIPS) PUB 180-4. SHA-2 was first published by the

National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...

(NIST) as a U.S. federal standard (FIPS). The SHA-2 family of algorithms are patented in US. The United States has released the patent under a royalty-free license. As of 2011, the best public attacks break

preimage resistance In cryptography, a preimage attack on cryptographic hash functions tries to find a message that has a specific hash value. A cryptographic hash function should resist attacks on its preimage (set of possible inputs). In the context of attack, the ...

for 52 out of 64 rounds of SHA-256 or 57 out of 80 rounds of SHA-512, and

collision resistance In cryptography, collision resistance is a property of cryptographic hash functions: a hash function ''H'' is collision-resistant if it is hard to find two inputs that hash to the same output; that is, two inputs ''a'' and ''b'' where ''a'' ≠ '' ...

for 46 out of 64 rounds of SHA-256.

Hash standard

With the publication of FIPS PUB 180-2, NIST added three additional hash functions in the SHA family. The algorithms are collectively known as SHA-2, named after their digest lengths (in bits): SHA-256, SHA-384, and SHA-512. The algorithms were first published in 2001 in the draft FIPS PUB 180-2, at which time public review and comments were accepted. In August 2002, FIPS PUB 180-2 became the new Secure Hash Standard, replacing FIPS PUB 180-1, which was released in April 1995. The updated standard included the original SHA-1 algorithm, with updated technical notation consistent with that describing the inner workings of the SHA-2 family.Federal Register Notice 02-21599
Announcing Approval of FIPS Publication 180-2
/ref> In February 2004, a change notice was published for FIPS PUB 180-2, specifying an additional variant, SHA-224, defined to match the key length of two-key

Triple DES In cryptography, Triple DES (3DES or TDES), officially the Triple Data Encryption Algorithm (TDEA or Triple DEA), is a symmetric-key block cipher, which applies the DES cipher algorithm three times to each data block. The Data Encryption Standa ...

. In October 2008, the standard was updated in FIPS PUB 180-3, including SHA-224 from the change notice, but otherwise making no fundamental changes to the standard. The primary motivation for updating the standard was relocating security information about the hash algorithms and recommendations for their use to Special Publications 800-107 and 800-57.FIPS SP 800-10
Recommendation for Applications Using Approved Hash Algorithms
/ref>FIPS SP 800-5
Recommendation for Key Management: Part 1: General
/ref> Detailed test data and example message digests were also removed from the standard, and provided as separate documents. In January 2011, NIST published SP800-131A, which specified a move from the then-current minimum of 80-bit security (provided by SHA-1) allowable for federal government use until the end of 2013, to 112-bit security (provided by SHA-2) being both the minimum requirement (starting in 2014) and the recommended security level (starting from the publication date in 2011). In March 2012, the standard was updated in FIPS PUB 180-4, adding the hash functions SHA-512/224 and SHA-512/256, and describing a method for generating initial values for truncated versions of SHA-512. Additionally, a restriction on

padding Padding is thin cushioned material sometimes added to clothes. Padding may also be referred to as batting when used as a layer in lining quilts or as a packaging or stuffing material. When padding is used in clothes, it is often done in an attempt ...

the input data prior to hash calculation was removed, allowing hash data to be calculated simultaneously with content generation, such as a real-time video or audio feed. Padding the final data block must still occur prior to hash output. In July 2012, NIST revised SP800-57, which provides guidance for cryptographic key management. The publication disallowed creation of digital signatures with a hash security lower than 112 bits after 2013. The previous revision from 2007 specified the cutoff to be the end of 2010. In August 2012, NIST revised SP800-107 in the same manner. The

NIST hash function competition 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 an ...

selected a new hash function,

SHA-3 SHA-3 (Secure Hash Algorithm 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 struc ...

, in 2012. The SHA-3 algorithm is not derived from SHA-2.

Applications

The SHA-2 hash function is implemented in some widely used security applications and protocols, including TLS and SSL, PGP,

SSH The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution. SSH applications are based on ...

S/MIME S/MIME (Secure/Multipurpose Internet Mail Extensions) is a standard for public key encryption and signing of MIME data. S/MIME is on an IETF standards track and defined in a number of documents, most importantly . It was originally developed by R ...

, and

IPsec In computing, Internet Protocol Security (IPsec) is a secure network protocol suite that authenticates and encrypts packets of data to provide secure encrypted communication between two computers over an Internet Protocol network. It is used in ...

. SHA-256 is used for authenticating Debian software packages and in the

DKIM DomainKeys Identified Mail (DKIM) is an email authentication method designed to detect forged sender addresses in email (email spoofing), a technique often used in phishing and email spam. DKIM allows the receiver to check that an email claimed ...

message signing standard; SHA-512 is part of a system to authenticate archival video from the International Criminal Tribunal of the Rwandan genocide. SHA-256 and SHA-512 are proposed for use in

DNSSEC The Domain Name System Security Extensions (DNSSEC) are a suite of extension specifications by the Internet Engineering Task Force (IETF) for securing data exchanged in the Domain Name System (DNS) in Internet Protocol (IP) networks. The protoc ...

. Unix and Linux vendors are moving to using 256- and 512-bit SHA-2 for secure password hashing. Several cryptocurrencies, including Bitcoin, use SHA-256 for verifying transactions and calculating

proof of work Proof of work (PoW) is a form of cryptographic proof in which one party (the ''prover'') proves to others (the ''verifiers'') that a certain amount of a specific computational effort has been expended. Verifiers can subsequently confirm this expe ...

proof of stake Proof-of-stake (PoS) protocols are a class of consensus mechanisms for blockchains that work by selecting validators in proportion to their quantity of holdings in the associated cryptocurrency. This is done to avoid the computational cost of ...

. The rise of ASIC SHA-2 accelerator chips has led to the use of

scrypt In cryptography, scrypt (pronounced "ess crypt") is a password-based key derivation function created by Colin Percival in March 2009, originally for the Tarsnap online backup service. The algorithm was specifically designed to make it costly ...

-based proof-of-work schemes. SHA-1 and SHA-2 are the Secure Hash Algorithms required by law for use in certain U.S. Government applications, including use within other cryptographic algorithms and protocols, for the protection of sensitive unclassified information. FIPS PUB 180-1 also encouraged adoption and use of SHA-1 by private and commercial organizations. SHA-1 is being retired for most government uses; the U.S. National Institute of Standards and Technology says, "Federal agencies ''should'' stop using SHA-1 for...applications that require collision resistance as soon as practical, and must use the SHA-2 family of hash functions for these applications after 2010" (emphasis in original). NIST's directive that U.S. government agencies must stop uses of SHA-1 after 2010 was hoped to accelerate migration away from SHA-1. The SHA-2 functions were not quickly adopted initially, despite better security than SHA-1. Reasons might include lack of support for SHA-2 on systems running Windows XP SP2 or older and a lack of perceived urgency since SHA-1 collisions had not yet been found. The Google Chrome team announced a plan to make their web browser gradually stop honoring SHA-1-dependent TLS certificates over a period from late 2014 and early 2015. Similarly, Microsoft announced that

Internet Explorer Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, commonly abbreviated IE or MSIE) is a series of graphical web browsers developed by Microsoft which was used in the Windows line of operating systems ( ...

and

Edge Edge or EDGE may refer to: Technology Computing * Edge computing, a network load-balancing system * Edge device, an entry point to a computer network * Adobe Edge, a graphical development application * Microsoft Edge, a web browser developed ...

would stop honoring public SHA-1-signed TLS certificates from February 2017.

Mozilla Mozilla (stylized as moz://a) is a free software community founded in 1998 by members of Netscape. The Mozilla community uses, develops, spreads and supports Mozilla products, thereby promoting exclusively free software and open standards, w ...

disabled SHA-1 in early January 2016, but had to re-enable it temporarily via a

Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current ...

update, after problems with web-based user interfaces of some router models and security appliances.

Cryptanalysis and validation

For a hash function for which ''L'' is the number of

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...

s in the

message digest A cryptographic hash function (CHF) is a hash algorithm (a map of an arbitrary binary string to a binary string with fixed size of n bits) that has special properties desirable for cryptography: * the probability of a particular n-bit output ...

, finding a message that corresponds to a given message digest can always be done using a brute force search in 2^''L'' evaluations. This is called a

preimage attack In cryptography, a preimage attack on cryptographic hash functions tries to find a message that has a specific hash value. A cryptographic hash function should resist attacks on its preimage (set of possible inputs). In the context of attack, the ...

and may or may not be practical depending on ''L'' and the particular computing environment. The second criterion, finding two different messages that produce the same message digest, known as a

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

, requires on average only 2^''L''/2 evaluations using a birthday attack. Some of the applications that use cryptographic hashes, such as password storage, are only minimally affected by a

collision attack In cryptography, a collision attack on a cryptographic hash tries to find two inputs producing the same hash value, i.e. a hash collision. This is in contrast to a preimage attack where a specific target hash value is specified. There are roughl ...

. Constructing a password that works for a given account requires a preimage attack, as well as access to the hash of the original password (typically in the

shadow 




A shadow is a dark area where light from a light source is blocked by an  opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette,  ...

file) which may or may not be trivial. Reversing password encryption (e.g., to obtain a password to try against a user's account elsewhere) is not made possible by the attacks. (However, even a secure password hash cannot prevent brute-force attacks on weak passwords.) In the case of document signing, an attacker could not simply fake a signature from an existing document—the attacker would have to produce a pair of documents, one innocuous and one damaging, and get the private key holder to sign the innocuous document. There are practical circumstances in which this is possible; until the end of 2008, it was possible to create forged SSL certificates using an MD5 collision which would be accepted by widely used web browsers. Increased interest in cryptographic hash analysis during the SHA-3 competition produced several new attacks on the SHA-2 family, the best of which are given in the table below. Only the collision attacks are of practical complexity; none of the attacks extend to the full round hash function. At FSE 2012, researchers at

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professiona ...

gave a presentation suggesting pseudo-collision attacks could be extended to 52 rounds on SHA-256 and 57 rounds on SHA-512 by building upon the biclique pseudo-preimage attack.

Official validation

Implementations of all FIPS-approved security functions can be officially validated through the CMVP program, jointly run by the

(NIST) and the

Communications Security Establishment The Communications Security Establishment (CSE; french: Centre de la sécurité des télécommunications, ''CST''), formerly (from 2008-2014) called the Communications Security Establishment Canada (CSEC), is the Government of Canada's national ...

(CSE). For informal verification, a package to generate a high number of test vectors is made available for download on the NIST site; the resulting verification, however, does not replace the formal CMVP validation, which is required by law for certain applications. , there are over 1300 validated implementations of SHA-256 and over 900 of SHA-512, with only 5 of them being capable of handling messages with a length in bits not a multiple of eight while supporting both variants.

Test vectors

Hash values of an empty string (i.e., a zero-length input text). 0x d14a028c2a3a2bc9476102bb288234c415a2b01f828ea62ac5b3e42f 0x e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 0x 38b060a751ac96384cd9327eb1b1e36a21fdb71114be07434c0cc7bf63f6e1da274edebfe76f65fbd51ad2f14898b95b 0x cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e 0x 6ed0dd02806fa89e25de060c19d3ac86cabb87d6a0ddd05c333b84f4 0x c672b8d1ef56ed28ab87c3622c5114069bdd3ad7b8f9737498d0c01ecef0967a Even a small change in the message will (with overwhelming probability) result in a mostly different hash, due to the

avalanche effect In cryptography, the avalanche effect is the desirable property of cryptographic algorithms, typically block ciphers and cryptographic hash functions, wherein if an input is changed slightly (for example, flipping a single bit), the output changes ...

. For example, adding a period to the end of the following sentence changes almost half (111 out of 224) of the bits in the hash: 0x 730e109bd7a8a32b1cb9d9a09aa2325d2430587ddbc0c38bad911525 0x 619cba8e8e05826e9b8c519c0a5c68f4fb653e8a3d8aa04bb2c8cd4c

Pseudocode

Pseudocode for the SHA-256 algorithm follows. Note the great increase in mixing between bits of the w[16..63] words compared to SHA-1. h0 := 0x6a09e667 h1 := 0xbb67ae85 h2 := 0x3c6ef372 h3 := 0xa54ff53a h4 := 0x510e527f h5 := 0x9b05688c h6 := 0x1f83d9ab h7 := 0x5be0cd19 k[0..63] := 0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da, 0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070, 0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2 begin with the original message of length L bits append a single '1' bit append K '0' bits, where K is the minimum number >= 0 such that (L + 1 + K + 64) is a multiple of 512 append L as a 64-bit big-endian integer, making the total post-processed length a multiple of 512 bits such that the bits in the message are: 1 , (the number of bits will be a multiple of 512) break message into 512-bit chunks for each chunk create a 64-entry message schedule array w[0..63] of 32-bit words copy chunk into first 16 words w ..15of the message schedule array for i from 16 to 63 s0 := (w[i-15] rightrotate 7) xor (w[i-15] rightrotate 18) xor (w[i-15] rightshift 3) s1 := (w[i-2] rightrotate 17) xor (w[i-2] rightrotate 19) xor (w[i-2] rightshift 10) w[i] := w[i-16] + s0 + w[i-7] + s1 a := h0 b := h1 c := h2 d := h3 e := h4 f := h5 g := h6 h := h7 for i from 0 to 63 S1 := (e rightrotate 6) xor (e rightrotate 11) xor (e rightrotate 25) ch := (e and f) xor ((not e) and g) temp1 := h + S1 + ch + k[i] + w[i] S0 := (a rightrotate 2) xor (a rightrotate 13) xor (a rightrotate 22) maj := (a and b) xor (a and c) xor (b and c) temp2 := S0 + maj h := g g := f f := e e := d + temp1 d := c c := b b := a := temp1 + temp2 h0 := h0 + a h1 := h1 + b h2 := h2 + c h3 := h3 + d h4 := h4 + e h5 := h5 + f h6 := h6 + g h7 := h7 + h digest := hash := h0 append h1 append h2 append h3 append h4 append h5 append h6 append h7 The computation of the ch and maj values can be optimized the same way as described for SHA-1. SHA-224 is identical to SHA-256, except that: * the initial hash values h0 through h7 are different, and * the output is constructed by omitting h7. h[0..7] := 0xc1059ed8, 0x367cd507, 0x3070dd17, 0xf70e5939, 0xffc00b31, 0x68581511, 0x64f98fa7, 0xbefa4fa4 SHA-512 is identical in structure to SHA-256, but: * the message is broken into 1024-bit chunks, * the initial hash values and round constants are extended to 64 bits, * there are 80 rounds instead of 64, * the message schedule array w has 80 64-bit words instead of 64 32-bit words, * to extend the message schedule array w, the loop is from 16 to 79 instead of from 16 to 63, * the round constants are based on the first 80 primes 2..409, * the word size used for calculations is 64 bits long, * the appended length of the message (before pre-processing), in ''bits'', is a 128-bit big-endian integer, and * the shift and rotate amounts used are different. h[0..7] := 0x6a09e667f3bcc908, 0xbb67ae8584caa73b, 0x3c6ef372fe94f82b, 0xa54ff53a5f1d36f1, 0x510e527fade682d1, 0x9b05688c2b3e6c1f, 0x1f83d9abfb41bd6b, 0x5be0cd19137e2179 k[0..79] := 0x428a2f98d728ae22, 0x7137449123ef65cd, 0xb5c0fbcfec4d3b2f, 0xe9b5dba58189dbbc, 0x3956c25bf348b538, 0x59f111f1b605d019, 0x923f82a4af194f9b, 0xab1c5ed5da6d8118, 0xd807aa98a3030242, 0x12835b0145706fbe, 0x243185be4ee4b28c, 0x550c7dc3d5ffb4e2, 0x72be5d74f27b896f, 0x80deb1fe3b1696b1, 0x9bdc06a725c71235, 0xc19bf174cf692694, 0xe49b69c19ef14ad2, 0xefbe4786384f25e3, 0x0fc19dc68b8cd5b5, 0x240ca1cc77ac9c65, 0x2de92c6f592b0275, 0x4a7484aa6ea6e483, 0x5cb0a9dcbd41fbd4, 0x76f988da831153b5, 0x983e5152ee66dfab, 0xa831c66d2db43210, 0xb00327c898fb213f, 0xbf597fc7beef0ee4, 0xc6e00bf33da88fc2, 0xd5a79147930aa725, 0x06ca6351e003826f, 0x142929670a0e6e70, 0x27b70a8546d22ffc, 0x2e1b21385c26c926, 0x4d2c6dfc5ac42aed, 0x53380d139d95b3df, 0x650a73548baf63de, 0x766a0abb3c77b2a8, 0x81c2c92e47edaee6, 0x92722c851482353b, 0xa2bfe8a14cf10364, 0xa81a664bbc423001, 0xc24b8b70d0f89791, 0xc76c51a30654be30, 0xd192e819d6ef5218, 0xd69906245565a910, 0xf40e35855771202a, 0x106aa07032bbd1b8, 0x19a4c116b8d2d0c8, 0x1e376c085141ab53, 0x2748774cdf8eeb99, 0x34b0bcb5e19b48a8, 0x391c0cb3c5c95a63, 0x4ed8aa4ae3418acb, 0x5b9cca4f7763e373, 0x682e6ff3d6b2b8a3, 0x748f82ee5defb2fc, 0x78a5636f43172f60, 0x84c87814a1f0ab72, 0x8cc702081a6439ec, 0x90befffa23631e28, 0xa4506cebde82bde9, 0xbef9a3f7b2c67915, 0xc67178f2e372532b, 0xca273eceea26619c, 0xd186b8c721c0c207, 0xeada7dd6cde0eb1e, 0xf57d4f7fee6ed178, 0x06f067aa72176fba, 0x0a637dc5a2c898a6, 0x113f9804bef90dae, 0x1b710b35131c471b, 0x28db77f523047d84, 0x32caab7b40c72493, 0x3c9ebe0a15c9bebc, 0x431d67c49c100d4c, 0x4cc5d4becb3e42b6, 0x597f299cfc657e2a, 0x5fcb6fab3ad6faec, 0x6c44198c4a475817 S0 := (a rightrotate 28) xor (a rightrotate 34) xor (a rightrotate 39) S1 := (e rightrotate 14) xor (e rightrotate 18) xor (e rightrotate 41) s0 := (w[i-15] rightrotate 1) xor (w[i-15] rightrotate 8) xor (w[i-15] rightshift 7) s1 := (w[i-2] rightrotate 19) xor (w[i-2] rightrotate 61) xor (w[i-2] rightshift 6) SHA-384 is identical to SHA-512, except that: * the initial hash values h0 through h7 are different (taken from the 9th through 16th primes), and * the output is constructed by omitting h6 and h7. h[0..7] := 0xcbbb9d5dc1059ed8, 0x629a292a367cd507, 0x9159015a3070dd17, 0x152fecd8f70e5939, 0x67332667ffc00b31, 0x8eb44a8768581511, 0xdb0c2e0d64f98fa7, 0x47b5481dbefa4fa4 SHA-512/t is identical to SHA-512 except that: * the initial hash values h0 through h7 are given by the ''SHA-512/t IV generation function'', * the output is constructed by truncating the concatenation of h0 through h7 at ''t'' bits, * ''t'' equal to 384 is not allowed, instead SHA-384 should be used as specified, and * ''t'' values 224 and 256 are especially mentioned as approved. The ''SHA-512/t IV generation function'' evaluates a ''modified SHA-512'' on the ASCII string "SHA-512/''t''", substituted with the decimal representation of ''t''. The ''modified SHA-512'' is the same as SHA-512 except its initial values h0 through h7 have each been XORed with the hexadecimal constant 0xa5a5a5a5a5a5a5a5. Sample C implementation for SHA-2 family of hash functions can be found in RFC 6234.

Comparison of SHA functions

In the table below, ''internal state'' means the "internal hash sum" after each compression of a data block. In the bitwise operations column, "Rot" stands for rotate no carry, and "Shr" stands for right logical shift. All of these algorithms employ modular addition in some fashion except for SHA-3. More detailed performance measurements on modern processor architectures are given in the table below. The performance numbers labeled 'x86' were running using 32-bit code on 64-bit processors, whereas the 'x86-64' numbers are native 64-bit code. While SHA-256 is designed for 32-bit calculations, it does benefit from code optimized for 64-bit processors on the x86 architecture. 32-bit implementations of SHA-512 are significantly slower than their 64-bit counterparts. Variants of both algorithms with different output sizes will perform similarly, since the message expansion and compression functions are identical, and only the initial hash values and output sizes are different. The best implementations of MD5 and SHA-1 perform between 4.5 and 6 cycles per byte on modern processors. Testing was performed by the

University of Illinois at Chicago The University of Illinois Chicago (UIC) is a public research university in Chicago, Illinois. Its campus is in the Near West Side community area, adjacent to the Chicago Loop. The second campus established under the University of Illinois ...

on their hydra8 system running an Intel Xeon E3-1275 V2 at a clock speed of 3.5 GHz, and on their hydra9 system running an AMD A10-5800K APU at a clock speed of 3.8 GHz. The referenced cycles per byte speeds above are the median performance of an algorithm digesting a 4,096 byte message using the SUPERCOP cryptographic benchmarking software. The MiB/s performance is extrapolated from the CPU clockspeed on a single core; real-world performance will vary due to a variety of factors.

Implementations

Below is a list of cryptography libraries that support SHA-2: * Botan * Bouncy Castle * Cryptlib * Crypto++ * Libgcrypt *

Mbed TLS Mbed TLS (previously PolarSSL) is an implementation of the TLS and SSL protocols and the respective cryptographic algorithms and support code required. It is distributed under the Apache License version 2.0. Stated on the website is that Mbed ...

libsodium NaCl (pronounced "salt") is an abbreviation for "Networking and Cryptography library", a public domain "...high-speed software library for network communication, encryption, decryption, signatures, etc". NaCl was created by the mathematician and ...

Nettle {{redirect, Nettle Nettle refers to plants with stinging hairs, particularly those of the genus '' Urtica''. It can also refer to plants which resemble ''Urtica'' species in appearance but do not have stinging hairs. Plants called "nettle" includ ...

LibreSSL LibreSSL is an open-source implementation of the Transport Layer Security (TLS) protocol. The implementation is named after Secure Sockets Layer (SSL), the deprecated predecessor of TLS, for which support was removed in release 2.3.0. The OpenBSD ...

* OpenSSL *

GnuTLS GnuTLS (, the GNU Transport Layer Security Library) is a free software implementation of the TLS, SSL and DTLS protocols. It offers an application programming interface (API) for applications to enable secure communication over the network trans ...

wolfSSL wolfSSL is a small, portable, embedded SSL/TLS library targeted for use by embedded systems developers. It is an open source implementation of TLS (SSL 3.0, TLS 1.0, 1.1, 1.2, 1.3, and DTLS 1.0, 1.2, and 1.3) written in the C programming langua ...

Hardware acceleration is provided by the following processor extensions: * Intel SHA extensions: Available on some Intel and AMD x86 processors. * VIA PadLock * ARMv8 Cryptography Extensions * IBM z/Architecture: Available since 2005 as part of the Message-Security-Assist Extensions 1 (SHA-256) and 2 (SHA-512)IBM z/Architecture Principles of Operation, publication number SA22-7832. See KIMD and KLMD instructions in Chapter 7. * IBM Power ISA since Since v 2.07

References

External links

Descriptions of SHA-256, SHA-384, and SHA-512
from NIST
SHA-2 Checker
– SHAChecker to check one's SSL compatibility for SHA-2
SHA-256 Calculator
– SHA-256 Calculator
Specifications for a Secure Hash Standard (SHS)
– Draft for proposed SHS (SHA-0)
Secure Hash Standard (SHS)
– Proposed SHS (SHA-0)

– Official NIST site for the Secure Hash Standard
FIPS PUB 180-4: Secure Hash Standard (SHS)
( PDF, 834 KB) – Current version of the Secure Hash Standard (SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512), August 2015
Test vectors for SHA-256/384/512
from the

NESSIE NESSIE (New European Schemes for Signatures, Integrity and Encryption) was a European research project funded from 2000 to 2003 to identify secure cryptographic primitives. The project was comparable to the NIST AES process and the Japanese Gov ...

project
Test vectors for SHA-1, SHA-2
from NIST site
NIST Cryptographic Hash Project
– SHA-3 competition * : "A 224-bit One-way Hash Function: SHA-224" * : "US Secure Hash Algorithms (SHA and SHA-based HMAC and HKDF)"; contains sample C implementation
SHA-256 algorithm demonstration
{{DEFAULTSORT:Sha-2 Cryptographic hash functions Articles with example pseudocode Checksum algorithms National Security Agency cryptography