ABSTRACT
This chapter discusses various aspects of block and stream ciphers. It introduces the substitution-permutation network as a design technique for block ciphers and discusses some standard attacks. The chapter looks at standards such as the Data Encryption Standard and Advanced Encryption Standard. Most modern-day block ciphers incorporate a sequence of permutation and substitution operations. Substitution-permutation networks (SPNs) have several attractive features. First, the design is simple and very efficient, in both hardware and software. In software, an S-box is usually implemented in the form of a look-up table. Linear cryptanalysis requires finding a set of linear approximations of S-boxes that can be used to derive a linear approximation of the entire SPN. Differential cryptanalysis is similar to linear cryptanalysis in many respects. Basically, CCM mode combines the use of counter mode (for encryption) with cipher block chaining (for authentication). There has been a considerable amount of research done on these various types of generators, including a variety of possible attacks.
