SHA-1 is a revision to SHA (Secure Hash Algorithm) that was defined in the Secure Hash Standard (SHS). This revision corrected a flaw in SHA. It is also described in ANSI X9.30.

The algorithm takes a message of less than 264 bits in length and produces a 160-bit message digest. This algorithm is slower, but more secure than MD5 because of the larger digest.

Reference: from RSA Laboratories' Frequently Asked Questions about Today's Cryptography 4.1, http://www.rsasecurity.com/rsalabs/faq/3-6-5.html.

Check out FIPS PUB 180-1 for the NIST description of SHA-1. It contains much more information than what is presented here.

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