Enigma

Enigma was a portable cipher machine used to encrypt and decrypt secret messages. More precisely, Enigma was a family of related electro-mechanical rotor machines — comprising a variety of different models.

The Enigma was used commercially from the early 1920s on, and was also adopted by the military and governmental services of a number of nations — most famously by Nazi Germany before and during World War II.

The German military model, the Wehrmacht Enigma, is the version most commonly discussed. The machine has gained notoriety because Allied cryptologists were able to decrypt a large number of messages that had been enciphered on the machine. The intelligence gained through this source — codenamed ULTRA — was a significant aid to the Allied war effort. The exact influence of ULTRA is debated, but a typical assessment is that the end of the European war was hastened by two years because of the decryption of German ciphers.

Although the Enigma cipher has cryptographic weaknesses, it was, in practice, only their combination with other significant factors which allowed codebreakers to read messages: mistakes by operators, procedural flaws, and the occasional captured machine or codebook.