SHA1
| Secure Hash Algorithm | |
|---|---|
 |
|
| Concepts | |
| hash functions · SHA · DSA | |
| Main standards | |
|
SHA-0 · SHA-1 · SHA-2 · SHA-3
|
|
| General | |
|---|---|
| Designers | National Security Agency |
| First published | 1993 (SHA-0), 1995 (SHA-1) |
| Series | (SHA-0), SHA-1, SHA-2, SHA-3 |
| Certification | FIPS PUB 180-4, CRYPTREC (Monitored) |
| Cipher detail | |
| Digest sizes | 160 bits |
| Block sizes | 512 bits |
| Structure | Merkle–Damgård construction |
| Rounds | 80 |
| Best public cryptanalysis | |
| A 2011 attack by Marc Stevens can produce hash collisions with a complexity between 260.3 and 265.3 operations. The first public collision was published on 23 February 2017. | |
In cryptography, SHA-1 (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. SHA-1 produces a 160-bit (20-byte) hash value known as a message digest. A SHA-1 hash value is typically rendered as a hexadecimal number, 40 digits long.
SHA-1 is no longer considered secure against well-funded opponents. In 2005, cryptanalysts found attacks on SHA-1 suggesting that the algorithm might not be secure enough for ongoing use, and since 2010 many organizations have recommended its replacement by SHA-2 or SHA-3.Microsoft,Google,Apple and Mozilla have all announced that their respective browsers will stop accepting SHA-1 SSL certificates by 2017.
On February 23, 2017 CWI Amsterdam and Google announced a practical collision attack against SHA-1, publishing two dissimilar PDF files which produce the same SHA-1 hash as proof of concept.
SHA-1 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.
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