The Enigma Machine was one of the center points of World War II, and its cryptanalysis was one of the stepping stones from breaking codes as art to cryptography as a science. The machine encrypted messages sent between parts of the German army – operators would type a key on its keyboard, the machine would scramble that, and a letter would light up on the top.
Enigma, a device used by the German military command to encode strategic messages before and during World War II. The Enigma code was first broken by the Poles, under the leadership of mathematician Marian Rejewski, in the early 1930s. In 1939, with the growing likelihood of a German invasion, the Poles turned their information over to the British, who set up a secret code-breaking group, known as Ultra, under mathematician Alan M. Turing. Because the Germans shared their encryption device with the Japanese, Ultra also contributed to Allied victories in the Pacific. See also Cryptology: Developments during World Wars I and II.
Most recently the story of how it was broken was the topic of the movie The Imitation Game.