Simple Substitution Ciphers

Abstract

Substitution ciphers are a rather unsophisticated and time-honoured class of ciphers, to the extent that one may feel that they appeal to aesthetical-minded mathematicians rather than to communications engineers or to computer scientists. However, one should not overlook the fact that individually weak ciphers can be combined into a network to give a hopefully strong cryptographic system: an obvious example here is the Data Encryption Standard, or DES, developed by IBM, which is built up by concatenating substitution and transposition ciphers.