Arthur Scherbius Patents the Enigma Rotor Cipher Machine for Commercial Message Encryption

Each keypress sent current through a set of cross-wired rotors that stepped with every letter, producing a constantly changing polyalphabetic substitution. Enigma was an offline device: an operator typed the plaintext, read or printed the ciphertext, and the result was sent as ordinary text by telegraph, telex, radio or post — the machine was never connected to telephone or telegraph lines. Early commercial models such as the printing "Handelsmaschine" and Enigma A were exhibited at the 1923–1924 Universal Postal Union congress; the reflector added in 1924 (an idea of Willi Korn) made later models compact and self-reciprocal, and the German armed forces adopted militarized versions from the mid-1920s.