The Data Encryption Standard (DES) and Alternatives

Abstract

The Data Encryption Standard (DES) has been by far the most popular block cipher for most of the last 30 years. Even though it is nowadays not considered secure against a determined attacker because the DES key space is too small, it is still used in legacy applications. Furthermore, encrypting data three times in a row with DES-a process referred to as 3DES or triple DES-yields a very secure cipher which is still widely used today (Section 3.5 deals with 3DES.) Perhaps what is more important, since DES is by far the best-studied symmetric algorithm, its design principles have inspired many current ciphers. Hence, studying DES helps us to understand many other symmetric algorithms. In this chapter you will learn: The design process of DES, which is very helpful for understanding the technical and political evolution of modern cryptography Basic design ideas of block ciphers, including confusion and diffusion, which are important properties of all modern block ciphers The internal structure of DES, including Feistel networks, S-boxes and the key schedule Security analysis of DES Alternatives to DES, including 3DES 55