The objective of this Standard is to specify three MAC algorithms that use a secret key and a hash-function (or its round-function) with an n-bit result to calculate an m-bit MAC. These mechanisms can be used as data integrity mechanisms to verify that data has not been altered in an unauthorized manner. They can also be used as message authentication mechanisms to provide assurance that a message has been originated by an entity in possession of the secret key. The strength of the data integrity and message authentication mechanisms is dependent on the entropy and secrecy of the key, on the length (in bits) n of a hash-code produced by the hash-function, on the strength of the hash-function, on the length (in bits) m of the MAC, and on the specific mechanism.