Alan Turing and an army of codebreakers took years to crack the Enigma code during the second world war. Just be thankful the Nazis weren't using a quantum Enigma machine. Quantum key distribution can already keep secret the key to a code. Enigma machines are like souped-up typewriters, with an illuminated panel above the keyboard that also displays the alphabet. Type in a letter and a different letter on the panel lights up, indicating how to encrypt that character. Wired rotors do the scrambling by guiding an electrical signal along a certain path.