CSA Preface Standards development within the Information Technology sector is harmonized with international standards development. Through the CSA Technical Committee on Information Technology (TCIT), Canadians serve as the Canadian Advisory Committee (CAC) on ISO/IEC Joint Technical Committee 1 on Information Technology (ISO/IEC JTC1) for the Standards Council of Canada (SCC), the ISO member body for Canada and sponsor of the Canadian National Committee of the IEC. Also, as a member of the International Telecommunication Union (ITU), Canada participates in the International Telegraph and Telephone Consultative Committee (ITU-T). This Standard supersedes CAN/CSA-ISO/IEC 9797-2-04 (adoption of ISO/IEC 9797-2:2002). At the time of publication, ISO/IEC 9797-2:2011 is available from ISO and IEC in English only. CSA Group will publish the French version when it becomes available from ISO and IEC. Scope This part of ISO/IEC 9797 specifies 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. The three mechanisms specified in this part of ISO/IEC 9797 are based on the dedicated hash-functions specified in ISO/IEC 10118-3. The first mechanism is commonly known as MDx-MAC. It calls the hash function once, but it makes a small modification to the round-function in the hash-function by adding a key to the additive constants in the round-function. The second mechanism is commonly known as HMAC. It calls the hash-function twice. The third mechanism is a variant of MDx-MAC that takes as input only short strings (at most 256 bits). It offers higher performance for applications that work with short input data strings only. This part of ISO/IEC 9797 can be applied to the security services of any security architecture, process, or application. NOTE A general framework for the provision of integrity services is specified in ISO/IEC 10181-6 [5].