Cryptography Reference
In-Depth Information
Chapter 3
The Data Encryption Standard (DES) and
Alternatives
The Data Encryption Standard (DES) has been by far the most popular block ci-
pher 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 de-
sign 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
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