Using Short Programs to Make and Break Historical Ciphers

Abstract

Introductory books on cryptography often start by studying a range of historical ciphers. This is attractive for two reasons: first, because there is some interesting related history (their success or failure is often aligned with an important event), and, second, because they are simple enough to understand without a significant background in Mathematics.

This chapter has a similar premise. The goal is to demonstrate the two sides of cryptography: the constructive side where new schemes (in this case for encryption) are designed and used, and the destructive side where said schemes are attacked and broken. By using simple programs available on every UNIX-based computer, the chapter demonstrates how historical cryptanalysts were able to decrypt messages their sender would probably have thought as secure.