Used by the German secret services, Enigma was an electro-mechanical machine that relied on a series of rotating wheels to scramble messages into a chaotic ciphertext. It was capable of producing billions of different combinations and was successfully designed to encrypt and decode highly sensitive messages.
Although it’s been used since the early Twenties it’s closely associated with the codebreakers of the allied forces – the British and Americans used the machine to secure intelligence from the Germans during WWII.
To unscramble messages, the codebreakers needed to know the Enigma setting used by the German operator before the message was encrypted. The German operators – both the sender and receiver – had to utilise their machines on identical settings recorded in codebooks and established before operations commenced.
Codebreakers approached enemy messages using a method called ‘Friedman’s Index of Coincidence’, which relied heavily on the mistakes and repetitive actions of the German operators in order to identify security flaws. This meant they could recognise patterns within the enemy codes and cryptanalyse their communications.
Mathematicians at Bletchley Park went on to develop the Bombe machine, designed to identify repetitive words and phrases in the messages and help them to guess at the meaning of the shorter parts of the messages. These were called ‘cribs’.