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RSA Laboratories

3.6.5 What are SHA and SHA-1?

The Secure Hash Algorithm (SHA), the algorithm specified in the Secure Hash Standard (SHS, FIPS 180), was developed by NIST (see Question 6.2.1) [NIS93a]. SHA-1 [NIS94c] is a revision to SHA that was published in 1994; the revision corrected an unpublished flaw in SHA. Its design is very similar to the MD4 family of hash functions developed by Rivest (see Question 3.6.6). SHA-1 is also described in the ANSI X9.30 (part 2) standard.

The algorithm takes a message of less than 264 bits in length and produces a 160-bit message digest. The algorithm is slightly slower than MD5 (see Question 3.6.6), but the larger message digest makes it more secure against brute-force collision and inversion attacks (see Question 2.1.6). SHA is part of the Capstone project (see Question 6.2.3). For further information on SHA, see [Pre93] and [Rob95b].

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