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Definition: SHA


(Secure Hash Algorithm) A family of popular cryptographic hash algorithms used to create digital signatures. The 160-bit SHA was developed by the National Institute of Standards & Technology (NIST) in 1993, and SHA-1 was the first revision in 1994. SHA-1 is similar to the MD4 and MD5 algorithms developed by Rivest, but is slightly slower and more secure. See MD5.

SHA-2 and SHA-3
Released in 2001, the stronger SHA-2 version superseded SHA-1. Because computers are increasingly more powerful, the stronger algorithm is encouraged by certificate authorities (CAs) to prevent an attacker from impersonating a CA. SHA-256 and SHA-512 are SHA-2 algorithms using hash lengths of 256 and 512 bits respectively, and SHA-224 and SHA-384 are truncated versions.

SHA-3 was released by NIST in 2015, which supports the same hash lengths as SHA-2 but uses a different cryptographic method based on the Keccak algorithm. SHA-3 was the result of a NIST competition for a new hash standard that began in 2006 and ended in 2012. See cryptographic hash function and digital signature.