SHA1
General  

Designers  National Security Agency 
First published  1993 (SHA0), 1995 (SHA1) 
Series  (SHA0), SHA1, SHA2, SHA3 
Certification  FIPS PUB 1804, CRYPTREC (Monitored) 
Detail  
Digest sizes  160 bits 
Structure  Merkle–Damgård construction 
Rounds  80 
Best public cryptanalysis  
A 2011 attack by Marc Stevens can produce hash collisions with a complexity between 2^{60.3} and 2^{65.3} operations.^{[1]} As of October 2015^{[update]}, no actual collisions are publicly known. 
In cryptography, SHA1 (Secure Hash Algorithm 1) is a cryptographic hash function designed by the United States National Security Agency and is a U.S. Federal Information Processing Standard published by the United States NIST.^{[2]} SHA1 is considered insecure against wellfunded opponents, and it is recommended to use SHA2 or SHA3 instead.^{[3]}^{[4]}
SHA1 produces a 160bit (20byte) hash value known as a message digest. A SHA1 hash value is typically rendered as a hexadecimal number, 40 digits long.
SHA1 is a member of the Secure Hash Algorithm family. The four SHA algorithms are structured differently and are named SHA0, SHA1, SHA2, and SHA3. SHA0 is the original version of the 160bit hash function published in 1993 under the name SHA: it was not adopted by many applications. Published in 1995, SHA1 is very similar to SHA0, but alters the original SHA hash specification to correct weaknesses that were unknown to the public at that time. SHA2, published in 2001, is significantly different from the SHA1 hash function.
In 2005, cryptanalysts found attacks on SHA1 suggesting that the algorithm might not be secure enough for ongoing use.^{[5]} NIST required many applications in federal agencies to move to SHA2 after 2010 because of the weakness.^{[6]} Although no successful attacks have yet been reported on SHA2, it is algorithmically similar to SHA1. In 2012, following a longrunning competition, NIST selected an additional algorithm, Keccak, for standardization under SHA3.^{[7]}^{[8]}
Microsoft,^{[9]} Google^{[10]} and Mozilla^{[11]}^{[12]}^{[13]} have all announced that their respective browsers will stop accepting SHA1 SSL certificates by 2017. Windows XP SP2 and earlier, and Android 2.2 and earlier, do not support SHA2 certificates.^{[14]}
Contents
The SHA1 hash function
This section does not cite any sources. (May 2013) 
SHA1 produces a message digest based on principles similar to those used by Ronald L. Rivest of MIT in the design of the MD4 and MD5 message digest algorithms, but has a more conservative design.
The original specification of the algorithm was published in 1993 under the title Secure Hash Standard, FIPS PUB 180, by U.S. government standards agency NIST (National Institute of Standards and Technology). This version is now often named SHA0. It was withdrawn by the NSA shortly after publication and was superseded by the revised version, published in 1995 in FIPS PUB 1801 and commonly designated SHA1. SHA1 differs from SHA0 only by a single bitwise rotation in the message schedule of its compression function; this was done, according to the NSA, to correct a flaw in the original algorithm which reduced its cryptographic security. However, the NSA did not provide any further explanation or identify the flaw that was corrected. Weaknesses have subsequently been reported in both SHA0 and SHA1. SHA1 appears to provide greater resistance to attacks^{[citation needed]}, supporting the NSA’s assertion that the change increased the security.
Applications
Cryptography
SHA1 forms part of several widely used security applications and protocols, including TLS and SSL, PGP, SSH, S/MIME, and IPsec. Those applications can also use MD5; both MD5 and SHA1 are descended from MD4. SHA1 hashing is also used in distributed revision control systems like Git, Mercurial, and Monotone to identify revisions, and to detect data corruption or tampering. The algorithm has also been used on Nintendo's Wii gaming console for signature verification when booting, but a significant flaw in the first implementations of the firmware allowed for an attacker to bypass the system's security scheme.^{[15]}
SHA1 and SHA2 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 1801 also encouraged adoption and use of SHA1 by private and commercial organizations. SHA1 is being retired from most government uses; the U.S. National Institute of Standards and Technology said, "Federal agencies should stop using SHA1 for...applications that require collision resistance as soon as practical, and must use the SHA2 family of hash functions for these applications after 2010" (emphasis in original),^{[16]} though that was later relaxed.^{[17]}
A prime motivation for the publication of the Secure Hash Algorithm was the Digital Signature Standard, in which it is incorporated.
The SHA hash functions have been used for the basis of the SHACAL block ciphers.
Data integrity
Revision control systems such as Git and Mercurial use SHA1 not for security but for ensuring that the data has not changed due to accidental corruption. Linus Torvalds has said about Git: "If you have disk corruption, if you have DRAM corruption, if you have any kind of problems at all, Git will notice them. It's not a question of if, it's a guarantee. You can have people who try to be malicious. They won't succeed. [...] Nobody has been able to break SHA1, but the point is the SHA1, as far as Git is concerned, isn't even a security feature. It's purely a consistency check. The security parts are elsewhere, so a lot of people assume that since Git uses SHA1 and SHA1 is used for cryptographically secure stuff, they think that, OK, it's a huge security feature. It has nothing at all to do with security, it's just the best hash you can get. [...] I guarantee you, if you put your data in Git, you can trust the fact that five years later, after it was converted from your hard disk to DVD to whatever new technology and you copied it along, five years later you can verify that the data you get back out is the exact same data you put in. [...] One of the reasons I care is for the kernel, we had a break in on one of the BitKeeper sites where people tried to corrupt the kernel source code repositories."^{[18]} Nonetheless, without the second preimage resistance of SHA1, signed commits and tags would no longer secure the state of the repository as they only sign the root of a Merkle tree.^{[citation needed]}
Cryptanalysis and validation
For a hash function for which L is the number of bits in the message digest, finding a message that corresponds to a given message digest can always be done using a brute force search in approximately 2^{L} evaluations. This is called a preimage attack 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, namely a collision, requires on average only about 1.2 × 2^{L/2} evaluations using a birthday attack. For the latter reason the strength of a hash function is usually compared to a symmetric cipher of half the message digest length. Thus SHA1 was originally thought to have 80bit strength.
Cryptographers have produced collision pairs for SHA0 and have found algorithms that should produce SHA1 collisions in far fewer than the originally expected 2^{80} evaluations.
In terms of practical security, a major concern about these new attacks is that they might pave the way to more efficient ones. Whether this is the case is yet to be seen, but a migration to stronger hashes is believed to be prudent. Some of the applications that use cryptographic hashes, like password storage, are only minimally affected by a collision attack. Constructing a password that works for a given account requires a preimage attack, as well as access to the hash of the original password, 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 can't prevent bruteforce 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.^{[19]}
Due to the block and iterative structure of the algorithms and the absence of additional final steps, all SHA functions (except SHA3^{[20]}) are vulnerable to lengthextension and partialmessage collision attacks.^{[21]} These attacks allow an attacker to forge a message signed only by a keyed hash – SHA(message  key) or SHA(key  message) – by extending the message and recalculating the hash without knowing the key. A simple improvement to prevent these attacks is to hash twice: SHA_{d}(message) = SHA(SHA(0^{b}  message)) (the length of 0^{b}, zero block, is equal to the block size of the hash function).
Attacks
In early 2005, Rijmen and Oswald published an attack on a reduced version of SHA1—53 out of 80 rounds—which finds collisions with a computational effort of fewer than 2^{80} operations.^{[22]}
In February 2005, an attack by Xiaoyun Wang, Yiqun Lisa Yin, and Hongbo Yu was announced.^{[23]} The attacks can find collisions in the full version of SHA1, requiring fewer than 2^{69} operations. (A bruteforce search would require 2^{80} operations.)
The authors write: "In particular, our analysis is built upon the original differential attack on SHA0 [sic], the near collision attack on SHA0, the multiblock collision techniques, as well as the message modification techniques used in the collision search attack on MD5. Breaking SHA1 would not be possible without these powerful analytical techniques."^{[24]} The authors have presented a collision for 58round SHA1, found with 2^{33} hash operations. The paper with the full attack description was published in August 2005 at the CRYPTO conference.
In an interview, Yin states that, "Roughly, we exploit the following two weaknesses: One is that the file preprocessing step is not complicated enough; another is that certain math operations in the first 20 rounds have unexpected security problems."^{[25]}
On 17 August 2005, an improvement on the SHA1 attack was announced on behalf of Xiaoyun Wang, Andrew Yao and Frances Yao at the CRYPTO 2005 rump session, lowering the complexity required for finding a collision in SHA1 to 2^{63}.^{[26]} On 18 December 2007 the details of this result were explained and verified by Martin Cochran.^{[27]}
Christophe De Cannière and Christian Rechberger further improved the attack on SHA1 in "Finding SHA1 Characteristics: General Results and Applications,"^{[28]} receiving the Best Paper Award at ASIACRYPT 2006. A twoblock collision for 64round SHA1 was presented, found using unoptimized methods with 2^{35} compression function evaluations. Since this attack requires the equivalent of about 2^{35} evaluations, it is considered to be a significant theoretical break.^{[29]} Their attack was extended further to 73 rounds (of 80) in 2010 by Grechnikov.^{[30]} In order to find an actual collision in the full 80 rounds of the hash function, however, massive amounts of computer time are required. To that end, a collision search for SHA1 using the distributed computing platform BOINC began August 8, 2007, organized by the Graz University of Technology. The effort was abandoned May 12, 2009 due to lack of progress.^{[31]}
At the Rump Session of CRYPTO 2006, Christian Rechberger and Christophe De Cannière claimed to have discovered a collision attack on SHA1 that would allow an attacker to select at least parts of the message.^{[32]}^{[33]}
In 2008, an attack methodology by Stéphane Manuel reported hash collisions with an estimated theoretical complexity of 2^{51} to 2^{57} operations.^{[34]} However he later retracted that claim after finding that local collision paths were not actually independent, and finally quoting for the most efficient a collision vector that was already known before this work.^{[35]}
Cameron McDonald, Philip Hawkes and Josef Pieprzyk presented a hash collision attack with claimed complexity 2^{52} at the Rump session of Eurocrypt 2009.^{[36]} However, the accompanying paper, "Differential Path for SHA1 with complexity O(2^{52})" has been withdrawn due to the authors' discovery that their estimate was incorrect.^{[37]}
One attack against SHA1 is Marc Stevens^{[38]} with an estimated cost of $2.77M to break a single hash value by renting CPU power from cloud servers.^{[39]} Stevens developed this attack in a project called HashClash,^{[40]} implementing a differential path attack. On 8 November 2010, he claimed he had a fully working nearcollision attack against full SHA1 working with an estimated complexity equivalent to 2^{57.5} SHA1 compressions. He estimates this attack can be extended to a full collision with a complexity around 2^{61}.
The SHAppening
On 8 October 2015, Marc Stevens, Pierre Karpman, and Thomas Peyrin published a freestart collision attack on SHA1's compression function that requires only 2^{57} SHA1 evaluations. This does not directly translate into a collision on the full SHA1 hash function (where an attacker is not able to freely choose the initial internal state), but undermines the security claims for SHA1. In particular, it is the first time that an attack on full SHA1 has been demonstrated; all earlier attacks were too expensive for their authors to carry them out. The authors named this significant breakthrough in the cryptanalysis of SHA1 The SHAppening.^{[3]}
The method was based on their earlier work, as well as the auxiliary paths (or boomerangs) speedup technique from Joux and Peyrin, and using high performance/cost efficient GPU cards from NVIDIA. The collision was found on a 16node cluster with a total of 64 graphics cards. The authors estimated that a similar collision could be found by buying 2K US$ of GPU time on EC2.^{[3]}
The authors estimate that the cost of renting EC2 CPU/GPU time enough to generate a full collision for SHA1 at the time of publication was between 75K–120K US$, and note that is well within the budget of criminal organizations, not to mention national intelligence agencies. As such, the authors recommend that SHA1 is deprecated as quickly as possible.^{[3]}
SHA0
At CRYPTO 98, two French researchers, Florent Chabaud and Antoine Joux, presented an attack on SHA0: collisions can be found with complexity 2^{61}, fewer than the 2^{80} for an ideal hash function of the same size.^{[41]}
In 2004, Biham and Chen found nearcollisions for SHA0—two messages that hash to nearly the same value; in this case, 142 out of the 160 bits are equal. They also found full collisions of SHA0 reduced to 62 out of its 80 rounds.
Subsequently, on 12 August 2004, a collision for the full SHA0 algorithm was announced by Joux, Carribault, Lemuet, and Jalby. This was done by using a generalization of the Chabaud and Joux attack. Finding the collision had complexity 2^{51} and took about 80,000 CPU hours on a supercomputer with 256 Itanium 2 processors. (Equivalent to 13 days of fulltime use of the computer.)
On 17 August 2004, at the Rump Session of CRYPTO 2004, preliminary results were announced by Wang, Feng, Lai, and Yu, about an attack on MD5, SHA0 and other hash functions. The complexity of their attack on SHA0 is 2^{40}, significantly better than the attack by Joux et al.^{[42]}^{[43]}
In February 2005, an attack by Xiaoyun Wang, Yiqun Lisa Yin, and Hongbo Yu was announced which could find collisions in SHA0 in 2^{39} operations.^{[23]}^{[44]}
Another attack in 2008 applying the boomerang attack brought the complexity of finding collisions down to 2^{33.6}, which is estimated to take 1 hour on an average PC.^{[45]}
In light of the results for SHA0, some experts^{[who?]} suggested that plans for the use of SHA1 in new cryptosystems should be reconsidered. After the CRYPTO 2004 results were published, NIST announced that they planned to phase out the use of SHA1 by 2010 in favor of the SHA2 variants.^{[46]}
Official validation
Implementations of all FIPSapproved security functions can be officially validated through the CMVP program, jointly run by the National Institute of Standards and Technology (NIST) and the Communications Security Establishment (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, in any way, the formal CMVP validation, which is required by law for certain applications.
As of December 2013^{[update]}, there are over 2000 validated implementations of SHA1, with 14 of them capable of handling messages with a length in bits not a multiple of eight (see SHS Validation List).
Examples and pseudocode
Example hashes
These are examples of SHA1 message digests in hexadecimal and in Base64 binary to ASCII text encoding.
SHA1("The quick brown fox jumps over the lazy dog") gives hexadecimal: 2fd4e1c67a2d28fced849ee1bb76e7391b93eb12 gives Base64 binary to ASCII text encoding: L9ThxnotKPzthJ7hu3bnORuT6xI=
Even a small change in the message will, with overwhelming probability, result in many bits changing due to the avalanche effect. For example, changing dog
to cog
produces a hash with different values for 81 of the 160 bits:
SHA1("The quick brown fox jumps over the lazy cog") gives hexadecimal: de9f2c7fd25e1b3afad3e85a0bd17d9b100db4b3 gives Base64 binary to ASCII text encoding: 3p8sf9JeGzr60+haC9F9mxANtLM=
The hash of the zerolength string is:
SHA1("") gives hexadecimal: da39a3ee5e6b4b0d3255bfef95601890afd80709 gives Base64 binary to ASCII text encoding: 2jmj7l5rSw0yVb/vlWAYkK/YBwk=
SHA1 pseudocode
Pseudocode for the SHA1 algorithm follows:
Note 1: All variables are unsigned 32bit quantities and wrap modulo 2^{32} when calculating, except for ml, the message length, which is a 64bit quantity, and hh, the message digest, which is a 160bit quantity. Note 2: All constants in this pseudo code are in big endian. Within each word, the most significant byte is stored in the leftmost byte position Initialize variables: h0 = 0x67452301 h1 = 0xEFCDAB89 h2 = 0x98BADCFE h3 = 0x10325476 h4 = 0xC3D2E1F0 ml = message length in bits (always a multiple of the number of bits in a character). Preprocessing: append the bit '1' to the message e.g. by adding 0x80 if message length is a multiple of 8 bits. append 0 ≤ k < 512 bits '0', such that the resulting message length in bits is congruent to −64 ≡ 448 (mod 512) append ml, in a 64bit bigendian integer. Thus, the total length is a multiple of 512 bits. Process the message in successive 512bit chunks: break message into 512bit chunks for each chunk break chunk into sixteen 32bit bigendian words w[i], 0 ≤ i ≤ 15 Extend the sixteen 32bit words into eighty 32bit words: for i from 16 to 79 w[i] = (w[i3] xor w[i8] xor w[i14] xor w[i16]) leftrotate 1 Initialize hash value for this chunk: a = h0 b = h1 c = h2 d = h3 e = h4 Main loop:^{[47]}^{[2]} for i from 0 to 79 if 0 ≤ i ≤ 19 then f = (b and c) or ((not b) and d) k = 0x5A827999 else if 20 ≤ i ≤ 39 f = b xor c xor d k = 0x6ED9EBA1 else if 40 ≤ i ≤ 59 f = (b and c) or (b and d) or (c and d) k = 0x8F1BBCDC else if 60 ≤ i ≤ 79 f = b xor c xor d k = 0xCA62C1D6 temp = (a leftrotate 5) + f + e + k + w[i] e = d d = c c = b leftrotate 30 b = a a = temp Add this chunk's hash to result so far: h0 = h0 + a h1 = h1 + b h2 = h2 + c h3 = h3 + d h4 = h4 + e Produce the final hash value (bigendian) as a 160 bit number: hh = (h0 leftshift 128) or (h1 leftshift 96) or (h2 leftshift 64) or (h3 leftshift 32) or h4
The number hh
is the message digest, which can be written in hexadecimal (base 16), but is often written using Base64 binary to ASCII text encoding.
The constant values used are chosen to be nothing up my sleeve numbers: the four round constants k
are 2^{30} times the square roots of 2, 3, 5 and 10. The first four starting values for h0
through h3
are the same with the MD5 algorithm, and the fifth (for h4
) is similar.
Instead of the formulation from the original FIPS PUB 1801 shown, the following equivalent expressions may be used to compute f
in the main loop above:
Bitwise choice between c and d, controlled by b. (0 ≤ i ≤ 19): f = d xor (b and (c xor d)) (alternative 1) (0 ≤ i ≤ 19): f = (b and c) xor ((not b) and d) (alternative 2) (0 ≤ i ≤ 19): f = (b and c) + ((not b) and d) (alternative 3) (0 ≤ i ≤ 19): f = vec_sel(d, c, b) (alternative 4) Bitwise majority function. (40 ≤ i ≤ 59): f = (b and c) or (d and (b or c)) (alternative 1) (40 ≤ i ≤ 59): f = (b and c) or (d and (b xor c)) (alternative 2) (40 ≤ i ≤ 59): f = (b and c) + (d and (b xor c)) (alternative 3) (40 ≤ i ≤ 59): f = (b and c) xor (b and d) xor (c and d) (alternative 4) (40 ≤ i ≤ 59): f = vec_sel(c, b, c xor d) (alternative 5)
Max Locktyukhin has also shown^{[48]} that for the rounds 32–79 the computation of:
w[i] = (w[i3] xor w[i8] xor w[i14] xor w[i16]) leftrotate 1
can be replaced with:
w[i] = (w[i6] xor w[i16] xor w[i28] xor w[i32]) leftrotate 2
This transformation keeps all operands 64bit aligned and, by removing the dependency of w[i]
on w[i3]
, allows efficient SIMD implementation with a vector length of 4 like x86 SSE instructions.
Comparison of SHA functions
In the table below, internal state means the "internal hash sum" after each compression of a data block.
Note that performance will vary not only between algorithms, but also with the specific implementation and hardware used. The OpenSSL tool has a builtin "speed" command that benchmarks the various algorithms on the user's system.
Algorithm and variant  Output size (bits) 
Internal state size (bits) 
Block size (bits) 
Max message size (bits) 
Rounds  Operations  Security (bits) 
Example performance^{[50]} (MiB/s) 


MD5 (as reference)  128  128 (4 × 32) 
512  Unlimited^{[51]}  64  And, Xor, Rot, Add (mod 2^{32}), Or  <64 (collisions found) 
335  
SHA0  160  160 (5 × 32) 
512  2^{64} − 1  80  And, Xor, Rot, Add (mod 2^{32}), Or  <80 (collisions found) 
  
SHA1  160  160 (5 × 32) 
512  2^{64} − 1  80  <80 (theoretical attack^{[52]}) 
192  
SHA2  SHA224 SHA256 
224 256 
256 (8 × 32) 
512  2^{64} − 1  64  And, Xor, Rot, Add (mod 2^{32}), Or, Shr  112 128 
139 
SHA384 SHA512 SHA512/224 SHA512/256 
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  
SHA3  SHA3224 SHA3256 SHA3384 SHA3512 
224 256 384 512 
1600 (5 × 5 × 64) 
1152 1088 832 576 
Unlimited^{[53]}  24^{[54]}  And, Xor, Rot, Not  112 128 192 256 
 
SHAKE128 SHAKE256 
d (arbitrary) d (arbitrary) 
1344 1088 
min(d/2, 128) min(d/2, 256) 
 
See also
 Comparison of cryptographic hash functions
 cryptlib
 Crypto++
 Digital timestamping
 Hashcash
 Hash collision
 International Association for Cryptologic Research
 Libgcrypt
 md5deep
 OpenSSL
 PolarSSL
 RIPEMD160
 Secure Hash Standard
 sha1sum
 Tiger (cryptography)
 Whirlpool (cryptography)
Notes
 ↑ Marc Stevens (19 June 2012). "Attacks on Hash Functions and Applications" (PDF). PhD thesis.
 ↑ ^{2.0} ^{2.1} http://csrc.nist.gov/publications/fips/fips1804/fips1804.pdf
 ↑ ^{3.0} ^{3.1} ^{3.2} ^{3.3} Stevens1, Marc; Karpman, Pierre; Peyrin, Thomas. "The SHAppening: freestart collisions for SHA1". Retrieved 20151009.
 ↑ Bruce Schneier (8 October 2015). "SHA1 Freestart Collision". Schneier on Security.
 ↑ Schneier, Bruce (February 18, 2005). "Schneier on Security: Cryptanalysis of SHA1".
 ↑ "NIST.gov  Computer Security Division  Computer Security Resource Center".
 ↑ "NIST Hash Workshop Liveblogging (5)  Schneier on Security".
 ↑ "heise online  ITNews, Nachrichten und Hintergründe". heise online.
 ↑ "SHA1 Deprecation Policy". Microsoft. 20131112. Archived from the original on 20131113. Retrieved 20131114.
 ↑ "Intent to Deprecate: SHA1 certificates". Google. 20140903. Retrieved 20140904.
 ↑ "Bug 942515  stop accepting SHA1based SSL certificates with notBefore >= 20140301 and notAfter >= 20170101, or any SHA1based SSL certificates after 20170101". Mozilla. Retrieved 20140904.
 ↑ "CA:Problematic Practices  MozillaWiki". Mozilla. Retrieved 20140909.
 ↑ "Phasing Out Certificates with SHA1 based Signature Algorithms  Mozilla Security Blog". Mozilla. 20140923. Retrieved 20140924.
 ↑ Zack Whittaker. "As sites move to SHA2 encryption, millions face HTTPS lockout". ZDNet.
 ↑ Felix "tmbinc" Domke (20080424). "Thank you, Datel.". Retrieved 20141005.
For verifiying the hash (which is the only thing they verify in the signature), they have chosen to use a function (strncmp) which stops on the first nullbyte – with a positive result. Out of the 160 bits of the SHA1hash, up to 152 bits are thrown away.
 ↑ National Institute on Standards and Technology Computer Security Resource Center, NIST's March 2006 Policy on Hash Functions, accessed September 28, 2012.
 ↑ National Institute on Standards and Technology Computer Security Resource Center, NIST's Policy on Hash Functions, accessed September 28, 2012.
 ↑ "Tech Talk: Linus Torvalds on git". Retrieved November 13, 2013.
 ↑ Alexander Sotirov, Marc Stevens, Jacob Appelbaum, Arjen Lenstra, David Molnar, Dag Arne Osvik, Benne de Weger, MD5 considered harmful today: Creating a rogue CA certificate, accessed March 29, 2009
 ↑ "Strengths of Keccak  Design and security". The Keccak sponge function family. Keccak team. Retrieved 20 September 2015.
Unlike SHA1 and SHA2, Keccak does not have the lengthextension weakness, hence does not need the HMAC nested construction. Instead, MAC computation can be performed by simply prepending the message with the key.
 ↑ Niels Ferguson, Bruce Schneier, and Tadayoshi Kohno, Cryptography Engineering, John Wiley & Sons, 2010. ISBN 9780470474242
 ↑ "Cryptology ePrint Archive: Report 2005/010".
 ↑ ^{23.0} ^{23.1} "SHA1 Broken  Schneier on Security".
 ↑ MIT.edu, Massachusetts Institute of Technology
 ↑ Robert Lemos. "Fixing a hole in security". ZDNet.
 ↑ "New Cryptanalytic Results Against SHA1  Schneier on Security".
 ↑ Notes on the Wang et al. 2^{63} SHA1 Differential Path
 ↑ Christophe De Cannière, Christian Rechberger (20061115). "Finding SHA1 Characteristics: General Results and Applications".
 ↑ "IAIK Krypto Group – Description of SHA1 Collision Search Project". Retrieved 20090630.
 ↑ "Collisions for 72step and 73step SHA1: Improvements in the Method of Characteristics". Retrieved 20100724.
 ↑ "SHA1 Collision Search Graz". Retrieved 20090630.
 ↑ "heise online  ITNews, Nachrichten und Hintergründe". heise online.
 ↑ "Crypto 2006 Rump Schedule".
 ↑ Stéphane Manuel. "Classification and Generation of Disturbance Vectors for Collision Attacks against SHA1" (PDF). Retrieved 20110519.
 ↑ Stéphane Manuel. "Classification and Generation of Disturbance Vectors for Collision Attacks against SHA1". Retrieved 20121004. the most efficient disturbance vector is Codeword2 first reported by Jutla and Patthak
 ↑ SHA1 collisions now 2^52
 ↑ "Cryptology ePrint Archive: Report 2009/259".
 ↑ Cryptanalysis of MD5 & SHA1
 ↑ "When Will We See Collisions for SHA1?  Schneier on Security".
 ↑ "Google Project Hosting".
 ↑ Florent Chabaud, Antoine Joux (1998). Differential Collisions in SHA0 (PDF). CRYPTO '98.
 ↑ "Report from Crypto 2004".
 ↑ Francois Grieu (18 August 2004). "Re: Any advance news from the crypto rump session?". Newsgroup: sci.crypt. Event occurs at 05:06:02 +0200. Usenet: fgrieu05A994.05060218082004@individual.net.
 ↑ (Chinese) Sdu.edu.cn, Shandong University
 ↑ Stéphane Manuel, Thomas Peyrin (20080211). "Collisions on SHA0 in One Hour".
 ↑ National Institute of Standards and Technology
 ↑ "RFC 3174  US Secure Hash Algorithm 1 (SHA1)".
 ↑ Locktyukhin, Max; Farrel, Kathy (20100331), "Improving the Performance of the Secure Hash Algorithm (SHA1)", Intel Software Knowledge Base, Intel, retrieved 20100402
 ↑ "Crypto++ 5.6.0 Benchmarks". Retrieved 20130613.
 ↑ Found on an AMD Opteron 8354 2.2 GHz processor running 64bit Linux^{[49]}
 ↑ "The MD5 MessageDigest Algorithm". Retrieved 20160418.
 ↑ "The SHAppening: freestart collisions for SHA1". Retrieved 20151105.
 ↑ "The Sponge Functions Corner". Retrieved 20160127.
 ↑ "The Keccak sponge function family". Retrieved 20160127.
References
 Florent Chabaud, Antoine Joux: Differential Collisions in SHA0. CRYPTO 1998. pp56–71
 Eli Biham, Rafi Chen, NearCollisions of SHA0, Cryptology ePrint Archive, Report 2004/146, 2004 (appeared on CRYPTO 2004), IACR.org
 Xiaoyun Wang, Hongbo Yu and Yiqun Lisa Yin, Efficient Collision Search Attacks on SHA0, CRYPTO 2005, CMU.edu
 Xiaoyun Wang, Yiqun Lisa Yin and Hongbo Yu, Finding Collisions in the Full SHA1, Crypto 2005 MIT.edu
 Henri Gilbert, Helena Handschuh: Security Analysis of SHA256 and Sisters. Selected Areas in Cryptography 2003: pp175–193
 unixwiz.net
 "Proposed Revision of Federal Information Processing Standard (FIPS) 180, Secure Hash Standard". Federal Register. 59 (131): 35317–35318. 19940711. Retrieved 20070426.
 A. Cilardo, L. Esposito, A. Veniero, A. Mazzeo, V. Beltran, E. Ayugadé, A CellBEbased HPC application for the analysis of vulnerabilities in cryptographic hash functions, High Performance Computing and Communication international conference, August 2010
External links
 CSRC Cryptographic Toolkit – Official NIST site for the Secure Hash Standard
 FIPS 1804: Secure Hash Standard (SHS) (PDF, 1.7 MB) – Current version of the Secure Hash Standard (SHA1, SHA224, SHA256, SHA384, and SHA512), March 2012
 RFC 3174 (with sample C implementation)
 Interview with Yiqun Lisa Yin concerning the attack on SHA1
 Explanation of the successful attacks on SHA1 (3 pages, 2006)
 Cryptography Research – Hash Collision Q&A
 Online SHA1 hash crack using Rainbow tables
 Hash Project Web Site: software and hardwarebased cryptanalysis of SHA1
 SHA1 at DMOZ
 Lecture on SHA1 on YouTube by Christof Paar
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 Broken hash functions
 Checksum algorithms
 National Security Agency cryptography