UMaC

UMAC stands for Universal Message Authentication Code, a family of cryptographic constructions designed to provide data integrity and authenticity for messages. A UMAC tag is computed from a secret key and the message, and can be verified only by someone who possesses the same key. Tags are typically 96 or 128 bits long, with some variants allowing longer tags for extra security. UMACs are designed to be fast on modern processors, especially 64-bit architectures, and to require modest memory.

Construction and operation typically involve two stages. First, a universal hash function processes the message into a short value using a secret key as part of the hashing process. Then a key-dependent finalization step maps that value to a fixed-length tag, often using a block cipher or a related primitive. The result is a MAC that can be computed efficiently in software and, with suitable hardware support, in parallel.

Security of UMAC rests on the properties of the universal hash family and the secrecy of the finalization function. When these components meet certain criteria, UMAC provides existential unforgeability under chosen-message attacks (EU-CMA) with a security level proportional to the tag length and the strength of the underlying primitives. This makes forging a valid tag for a new message computationally infeasible under standard cryptographic assumptions.

Variants of UMAC are optimized for different environments, including software and hardware implementations. It is used in contexts where high-speed message authentication is important and where the assumptions about the hash family and cipher hold. UMAC is discussed in cryptographic literature and implemented in select cryptographic libraries as an alternative to more common MAC constructions like HMAC or CMAC.