One-key MAC (OMAC) is a family of message authentication codes constructed from a block cipher much like the CBC-MAC algorithm. It may be used to provide assurance of the authenticity and, hence, the integrity of data. Two versions are defined:
- The original OMAC of February 2003, which is seldom used. The preferred name is now "OMAC2".
- The OMAC1 refinement, which became an NIST recommendation in May 2005 under the name CMAC.
