Introduction to Cryptography with Open-Source Software

Chapter 3

Classical cryptosystems

This chapter will consider

• The use of simple pencil-and-paper systems to give an insight into the

working, construction and uses of cryptosystems.

• Some simple means of cr yptanalysis.

• A tiny bit of modula r linear algebr a.

3.1 Introduction

This chapter will be concer ned with some simple cryptos ystems. None

of the systems described in this chapter a re ever used in practice, except in

puzzles and games. However, they are worth studying because they provide

very good insight into the structure and behavior of cryptosystems. Partly

this is because these systems work with letters of the alphabet, rather tha n

with