Enigma, named after the Greek word for ‘riddle’, is an encryption machine used to encrypt and decrypt messages. The Enigma features a series of code wheels that can be set to any one of 26 different positions. Before sending a message, the operator selects three code wheels from a set of five possible wheels, placing them in the machine in a specific order, as previously agreed with the recipient. The code wheels are then set to a basic position. While the operator enters a message, the encrypted message appears letter by letter in an illuminated window. Provided you know the exact settings of the code wheels, you can also decipher the message that was encrypted this way.
Project Ultra, which had the objective of deciphering the Enigma codes, was a source of many a headache for the allied forces, with more than one thousand people spending six years to decipher the codes. Project Ultra is managed out of a Victorian villa in Bletchley Park, in the English county of Buckinghamshire. In this villa, the British eavesdrop on German radio traffic day and night, attempting the decipher the messages they pick up. They succeed at times, giving the Allied forces access to secret information about Wehrmacht submarines, for instance, and the landing in Normandy.
The fact that the allies ultimately succeeded in cracking the Enigma is due to the weak links in human secrecy, extortion and eavesdropping, rather than the quality of the encryption machine.