Introduction to Cryptography with Coding Theory, 3rd Edition

6.3 Modes of Operation

Suppose we have a block cipher. It can encrypt a block of plaintext of a fixed size, for example 64 bits. There are many circumstances, however, where it is necessary to encrypt messages that are either longer or shorter than the cipher’s block length. For example, a bank may be sending a terabyte of data to another bank. Or you might be sending a short message that needs to be encrypted one letter at a time since you want to produce ciphertext output as quickly as you write the plaintext input.

Block ciphers can be run in many different modes of operation, allowing users to choose appropriate modes to meet the requirements of their applications. There are five common modes of operation: electronic codebook (ECB), cipher ...