An ANSI standard in cryptography for a short piece of information used to authenticate a message based on DES. A message authentication code involves an algorithm (often a one-way hash function or a block cipher) that accepts a secret key and a message as input; it then produces a MAC (sometimes known as a tag). This process provides both an integrity check (by ensuring that a different MAC will result if the message has been altered) and an authenticity check (because only the person knowing the secret key could have produced a MAC).

See Also: American National Standards Institute (ANSI); Authenticity; Data Encryption Standard (DES); Hash, One-Way; Integrity.