How the Enigma Machine Works

Ciphers

• Enigma uses a substitution cipher to encode messages. Each letter in the original message--known as plain text--is replaced by a different letter in the encoded cipher text message.

Rotors

• The letter used for the encoded message is selected by a series of rotors. Operators of military Enigma machines chose three rotors from a possible five to encode a message. Each time the operator encoded a letter of plain text, the rotors would move, so each letter was encoded differently.

Reflectors

• Reflectors added another level of security to the code by reflecting, or reversing, pairs of letters. Using its rotors and reflectors, the most basic Enigma machine performed seven substitutions on each letter of plain text it encoded.

Plugboard

• Military Enigma machines also included a plug board, which reversed pairs of letters in a similar way to the reflectors.

Decoding

• Ships, submarines and military units that received cipher text messages used their own Enigma machines to decode them. Code at the start of the message told them which settings to use.