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.