The Enigma (Greek aínigma, English “riddle”, proper spelling also: ENIGMA) is a rotor key machine that was used during World War II to encrypt message traffic.
The inventor of the Enigma was Arthur Scherbius, whose first patent for it was dated February 23, 1918. In the course of time until the end of the war in 1945 and even beyond, for example in Korea in 1965, many different models were used. The most used one was the Enigma I.
The Enigma I basically consists of a keyboard for entering letters, a set of three – later five – interchangeable rollers numbered with Roman numerals (I, II, III, IV and V), a light bulb field for display and a plug-in board.
The current from the letter key (2) is passed over this plug board (3) before it reaches the entry roller (4). After passing through the roller set, it flows a second time over the plug board (7, 8) and finally lights up one of the 26 letter lamps (9).
The Enigma is a polyalphabetic monographic substitution cipher with a stream cipher.