SHA, Secure Hash Algorithm

SHA functions are made up of five cryptographic techniques designed by the NSA (National Security Agency). They have since become a United States Federal Information Processing Standard. Hash algorithms are able to compute a fixed length representation, more commonly known as a message digest, of any length. The five algorithms include: SHA-1, SHA-224, SHA-256, SHA-384 and SHA-512. The last four variations are often collectively referred to as SHA-2. SHA-1 creates a message digest of 160-bits - the bit length created by the other four algorithms is denoted by their names - 224, 256, 384, and 512. SHA-1 is widely used in many security programs and protocols such as SSL, TLS, SSH, PGP, S/MIME and Ipsec. It is often called an extension of MD5, a hash function that was once popular. SHA hash functions are considered secure when meeting the following criteria: • it is irrational to find a message that corresponds to a specific message digest • it is irrational to find two separate messages that produce the same message digest • any change to a message will result in a totally different message digest