ENIGMA Encryption Machine

The Enigma encryption machine is quite possibly the most famous encryption device of all time. Invented in 1918 by the Germans, it was initially designed to secure banking communications, but achieved little success in that sphere. The German military, however, were quick to see its potential and the Enigma cypher became the backbone of German military and intelligence communications during World War II.

Due to its bewildering complexity Enigma was long thought to be unbreakable. The machine was based on a system of three rotors that substituted cipher text letters for plain text letters. The rotors would spin in conjunction with each other, thus performing varying substitutions. When a letter was typed on the keyboard of the machine, it was first sent through the first rotor, which would shift the letter according to its present setting. The new letter would then pass through the second rotor, where it would be replaced by a substitution according to the present setting of the second rotor. This new letter would in turn pass through the third rotor, again being substituted accordingly. Next, this new letter would be bounced off of a reflector, and back through the three rotors in reverse order.

All recipients would set their rotors to predetermined settings according to the date. Each operator had a book detailing the settings for each day. This presented a major weakness in the system. Obviously, if anyone could figure out what the settings of the rotors were for a particular day, they would be able to decode that day's messages. Otherwise the odds against anyone who did not know the settings being able to break Enigma were a staggering 150,000,000,000,000,000,000 to 1.

In 1932 the Poles had broken Enigma and even managed to reconstruct a machine. At that time, the cypher altered only once every few months, but with the advent of war started to change at least once a day. However in July 1939, they had passed on their knowledge to the British and the French, which enabled the codebreakers to make critical progress. In January 1940 came the first break into Enigma and the cipher was eventually broken by the mathematician Alan Turing and a group of scientists at Bletchley Park (UK).

Source: http://world-information.org/wio/program/objects/1037127970