The Enigma machine was a simple cipher machine used by the Germans in World War Two. It had several components: a plug board, a light board, a keyboard, a set of rotors, and a reflector (half rotor). The original machine looked a lot like a typewriter.

The machine has several variable settings that affect the operation of the machine. To encrypt a message, the sender set up these settings on the enigma engine, and then typed in the message. The machine changed each letter differently each time, so if you typed in the letter a twice, it would give a different result each time.

In order to decrypt a message, the receiver must have the encrypted message, and know which rotors were used, the connections on the plug board and the initial settings of the rotors. To decrypt a message, the receiver would set up the machine identically to the way the sender initially had it and would type in the encrypted message. The output of typing in the encrypted message would be the original message. Although the Germans didn't know, the Enigma machine was not secure. The number of possible encryptions was quite large but Polish mathematicians worked on breaking the systems. They obtained several Enigma machines and code books from captured U-boats.

Through the confiscated Enigma machines, and some developed machines, the mathematicians were able to break the codes. When Poland was invaded by the Germans, the mathematicians provided the British and the Americans with their work. The Germans resorted to more sophisticated Enigma machines using four rotors but by 1943, the codes were broken with some consistency, even though the Germans did not know the enemy were deciphering their messages.