More About Block Ciphers

Abstract

A block cipher is much more than just an encryption algorithm. It can be used as a versatile building block with which a diverse set of cryptographic mechanisms can be realized. For instance, we can use them for building different types of blockbased encryption schemes, and we can even use block ciphers for realizing stream ciphers. The different ways of encryption are called modes of operation and are discussed in this chapter. Block ciphers can also be used for constructing hash functions, message authentication codes which are also knowns as MACs, or key establishment protocols, all of which will be described in later chapters. There are also other uses for block ciphers, e.g., as pseudo-random generators. In addition tomodes of operation, this chapter also discusses two very useful techniques for increasing the security of block ciphers, namely key whitening and multiple encryption.