The Secure Hash Algorithm SHA (Secure Hash Algorithm), based on the MD4 (Message Digest) algorithm created by Ronald L. Rivest of the MIT. Consists in three SHA distinct algorithms labeled SHA-0, SHA-1, and SHA-2.

SHA-1 was considered a cryptographically secure one-way hash algorithm (some weaknesses have already been found). It was designed by the NIST (National Institute of Standards and Technology), along with the NSA (National Security Agency), see the Secure Hash Standard FIPS 180-1.