Chapter 8 Codes
Convert text into a sequence of numbers.
Apply substitution ciphers to encrypt and decrypt texts.
Apply frequency analysis to break Caesar ciphers.
In this chapter we apply functions in the encoding and encryption of texts. We first introduce a function that we use to represent characters by numbers in Section 8.1. This is followed by a short introduction to symmetric key cryptography in Section 8.2. and the description of simple symmetric key crypto systems, namely Caesar ciphers in Section 8.3 and other substitution ciphers in Section 8.4. We conclude this chapter with an attack on substitution ciphers called frequency analysis in Section 8.5.