CBC-MAC

CBC-MAC, the cipher block chaining message authentication code, is a technique for building a message authentication code from a block cipher. The message is encrypted with the block cipher in cipher block chaining mode, with a zero initialization vector, to make a chain of blocks in which each block depends on the proper encryption of the previous one, and only the last block is kept. A change to any plaintext bit therefore changes the final block in a way that cannot be predicted or counteracted without the key. On its own CBC-MAC is not secure for variable-length messages. It is currently used to construct a pseudorandom function family and as a component of the CCM mode.