Kevin Owens · Enigma and Turing's machine · The story · Enigma · The machine · 3D view

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Lit in turn: key, plugs, cable, wheels, rotor contacts, lampThree rotors from five; the pawls step them before the contacts closeThe wiring diagram: the same path, letter by letter, out and backPaletteThe Enigma I (Wehrmacht, 1932 onward) enciphers by sending a current from the pressed key through the Steckerbrett, the fixed entry wheel, three rotors right to left, the reflector, and back through the rotors, the entry wheel and the Steckerbrett to a lamp. Pressing the key first lifts the pawl bar: the right pawl always pushes the right rotor's ratchet one letter; the middle pawl drops into the right rotor's notch when it is under it and then turns the middle rotor too; the left pawl does the same on the middle rotor's notch, and because it pushes the middle rotor's notch as well, the middle rotor moves on two presses in a row (the double step). Only then do the contacts close. The wiring, notches and stepping here are the real ones (rotors I–V, reflectors A, B, C, from the Wikipedia table that cites cryptomuseum.com), checked against published vectors (I-II-III, B, rings AAA, start AAA: AAAAA → BDZGO). On the machine the parts the current passes through light in order; on each rotor a short arc glows on the contact it enters by (the entry wheel's contact A sits under the window, so contact c is where tyre letter c + window letter is), on the right edge of the tyre going out and the left edge coming back. The wiring diagram beside it is the same press drawn flat: nine columns of 26 contacts in the order the current meets them, a wire across each gap keeping its letter and a jump down each column where that part's wiring changes it, with the window letters over the rotor columns so the path can be seen to change as the rotors step. The default key is II-V-III, reflector B, rings BUL, start RKX, plugs AV BS CG DL FU HZ IN KM OW RX: the key Turing's codebreaking machine in the next figure breaks from the crib WETTERVORHERSAGE. The rotor bay here is drawn open, with the windows on a strip over the tyres; on the machine the inner lid covers the rotors and only the finger wheels and the window letters show.

The day's key