Block ciphers and modes of operation

Abstract

The basic description of a block cipher is shown in Figure 13.1. Block ciphers operate on blocks of plaintext one at a time to produce blocks of ciphertext. The block of plaintext and the block of ciphertext are assumed to be of the same size, e.g. a block of n bits. Every string of n bits in the domain should map to a string of n bits in the codomain, and every string of n bits in the codomain should result from the application of the function to a string in the domain. This means that for a fixed key a block cipher is bijective and hence is a permutation.