Security in Computing, Third Edition

2.2. Substitution Ciphers

Children sometimes devise “secret codes” that use a correspondence table with which to substitute a character or symbol for each character of the original message. This technique is called a monoalphabetic cipher or simple substitution. A substitution is an acceptable way of encrypting text. In this section, we study several kinds of substitution ciphers.

The Caesar Cipher

The Caesar cipher has an important place in history. Julius Caesar is said to have been the first to use this scheme, in which each letter is translated to a letter a fixed number of places after it in the alphabet. Caesar used a shift of 3, so that plaintext letter p_i was enciphered as ciphertext letter c_i by the rule

A full translation chart of ...