Card catalog (cryptology)

The result might be: He would use the lengths of the cycles (132;102-32;102-22-12) to look up the wheel order (II I III) and starting rotor positions in the card catalog.

Preparation of the card catalog, using the cyclometer that Rejewski had invented about 1934 or 1935, was a laborious task that took over a year's time.

But once the catalog was complete, obtaining Enigma daily keys was a matter of some fifteen minutes.

[2][3] When the Germans changed the Enigma machine's "reflector," or "reversing drum," on 1 November 1937, the Cipher Bureau was forced to start over again with a new card catalog: "a task," writes Rejewski, "which consumed, on account of our greater experience, probably somewhat less than a year's time.

"[2] On 15 September 1938 the Germans completely changed the procedure for enciphering message keys, rendering the card-catalog method useless.

This spurred the invention of Rejewski's cryptologic bomb and Henryk Zygalski's "perforated sheets.