(1) In Cryptographic Support, the first 4 bytes from the last 8-byte block of ciphertext produced when encrypting a message using cipher block chaining, that is added to the end of the plaintext message from which it was created and used to detect whether the message was changed during transmission.
(2) In computer security, a value that is a part of a message or accompanies a message and is used to determine that the contents, origin, author, or other attributes of all or part of the message are as they appear to be.