Introduction to Cryptography with Coding Theory, 3rd Edition

2.7 Enigma

Mechanical encryption devices known as rotor machines were developed in the 1920s by several people. The best known was designed by Arthur Scherbius and became the famous Enigma machine used by the Germans in World War II.

It was believed to be very secure and several attempts at breaking the system ended in failure. However, a group of three Polish cryptologists, Marian Rejewski, Henryk Zygalski, and Jerzy Różycki, succeeded in breaking early versions of Enigma during the 1930s. Their techniques were passed to the British in 1939, two months before Germany invaded Poland. The British extended the Polish techniques and successfully decrypted German messages throughout World War II.

The fact that Enigma had been broken remained a secret ...