Rejewski's Cyclometer
1934 · Cyclometer · Work 442 of 1,871
A low wooden box carrying two sets of cipher rotors wired in series, each set a row of three brass and bakelite discs side by side under an open hinged lid, a panel of small round lamps above them arranged in a grid, a row of toggle switches beneath the lamps, a large rheostat knob at the left and two battery terminals at the side, cloth covered wires running between the parts, a wooden card index box standing open beside the machine with a stack of blank ruled cards, the rotor rims plain polished metal, all of it on a scrubbed deal table, a single work lamp hanging low over the box, warm brass rims catching the light against the grey painted room behind.
- What it was used for
- A device of the Polish Cipher Bureau in Warsaw, used by Marian Rejewski to find the daily key of the German army Enigma. It held two coupled sets of Enigma rotors, offset by three positions, and a panel of 26 lamps. For each rotor setting it displayed the cycle lengths of the permutations AD, BE and CF. With it the Poles compiled a card catalogue of all 3! x 26³ = 105,456 rotor settings. Once the catalogue was finished, obtaining the daily key was, in Rejewski's own words, "usually a matter of ten to twenty minutes".
- What was new
- What was new was not decipherment but the fact that a property of the machine could be catalogued: the cycle lengths depend only on the wheel order and the starting position, not on the plugboard. Rejewski thereby split the problem into a part that can be computed once and then merely looked up, and a remainder. The barb is in the timing: by Rejewski's own account the catalogue took over a year because it was done alongside routine work - and on 2 November 1937, just as it was ready, the Germans exchanged the reflector A they had been using for a B drum. The Poles had to do the whole job again.
Connections
Every connection names its kind. “Forerunner” on its own would be a claim.
- Follows fromEnigma I with Plugboard1932Rejewski describes his own cyclometer: its main part is two assemblies of ciphering drums connected by leads carrying current, which flows alternately through both. It rested on the Polish reconstruction of the wiring of the Enigma that German military units used with a plugboard. The cyclometer, or rather the catalogue based on it, did its job until 15 September 1938.Source: Marian Rejewski: An Application of the Theory of Permutations in Breaking the Enigma Cipher. Applicationes Mathematicae 16 (1980), Nr. 4 (Neusatz von Enrico Grigolon und Frode Weierud, 2002)