CBC-MAC uses a block cipher of some block length n E N in CBC mode, with initial value = 0n (unencrypted!), where the MAC value is the last ciphertext block. We assume again for simplicity that the bit length of all messages is a multiple of n, i.e. messages have been padded appropriately prior to computing their authentication tags. Then the input to CBC-MAC is a message M consisting of L blocks P, 2,..., Pl, each of length n. Algorithmically. CBC-MAC can be described as follows (here, EK denotes encryption under the block cipher under key K). Algorithm CBC-MAGC CBC-MAC uses a block cipher of some block length n E N in CBC mode, with initial value = 0n (unencrypted!), where the MAC value is the last ciphertext block. We assume again for simplicity that the bit length of all messages is a multiple of n, i.e. messages have been padded appropriately prior to computing their authentication tags. Then the input to CBC-MAC is a message M consisting of L blocks P, 2,..., Pl, each of length n. Algorithmically. CBC-MAC can be described as follows (here, EK denotes encryption under the block cipher under key K). Algorithm CBC-MAGC