How the Enigma works

The German Enigma machine scrambled each letter through three rotors, a reflector and back, with a plugboard swapping letter pairs on the way in and out. After every key press the right-hand rotor turns, and at set points the others turn too, so the same letter comes out differently each time. Because the signal goes through the reflector, the machine is its own reverse: typing the coded message with the same settings gives back the original.

To decode, set the same three rotors, the reflector, the ring settings (Ringstellung), the starting positions and the plugboard pairs used to make the message, then type or paste it in. Ring settings and positions can be letters, like A A A, or numbers, like 01 01 01.

Accurate to the real machine

CacheCrack's Enigma includes the famous double step, where the middle rotor turns twice in a row, and the two turnover notches on rotors VI, VII and VIII. It was checked against an established Enigma simulator across many random settings. One quirk helps catch mistakes: a real Enigma never turns a letter into itself.

Example

With rotors I, II and III, reflector B, rings and positions A A A and no plugboard, AAAAA becomes BDZGO.