The card catalog, or "catalog of characteristics," in cryptology, was a system designed, and first completed about 1935, by Polish Cipher Bureau mathematician-cryptologist Marian Rejewski to facilitate decrypting German Enigma messages. The card catalog was produced over more than a year's time, using the cyclometer invented by Rejewski about 1934. Cryptography (from Greek kryptós, hidden, and gráphein, to write) is, traditionally, the study of means of converting information from its normal, comprehensible form into an incomprehensible format, rendering it unreadable without secret knowledge — the art of encryption. ... 1935 (MCMXXXV) was a common year starting on Tuesday (link will take you to calendar). ... The Biuro Szyfrów ( (?), Polish for Cipher Bureau) was the Polish agency concerned with cryptology between World Wars I and II. The Bureau enjoyed notable successes against Soviet cryptography during the Polish-Soviet War, helping to preserve Polands independence. ... Marian Rejewski (probably 1932, the year he first solved the Enigma machine). ... This article is about algorithms for encryption and decryption. ... A three-rotor German military Enigma machine showing, from bottom to top, the plugboard, the keyboard, the lamps and the finger-wheels of the rotors emerging from the inner lid (version with labels). ... Diagram of cyclometer, from Marian Rejewski’s papers The cyclometer was a cryptologic device designed by the Polish Cipher Bureau (BS-4) to help decrypt the German Enigma machine during the 1930s. ... 1934 (MCMXXXIV) was a common year starting on Monday (link will take you to calendar). ...

When the Germans changed the Enigma machine's "reflector," or "reversing drum," on November 1, 1937, the Cipher Bureau was forced to start over again and produce a new card catalog, "a task," writes Rejewski, "which consumed, on account of our greater experience, probably somewhat less than a year's time." A reflector, in cryptology, is a component of some rotor cipher machines, such as the Enigma machine, that sends electrical impulses that have reached it from the machines rotors, back in reverse order through those rotors. ... November 1 is the 305th day of the year (306th in leap years) in the Gregorian Calendar, with 60 days remaining. ... 1937 (MCMXXXVII) was a common year starting on Friday (link will take you to calendar). ...

On September 15, 1938, the Germans changed entirely the procedure for enciphering message keys, and as a result the card-catalog method became completely useless. This spurred the invention of Rejewski's cryptologic bomb and Henryk Zygalski's "perforated sheets." September 15 is the 258th day of the year (259th in leap years). ... 1938 (MCMXXXVIII) was a common year starting on Saturday (link will take you to calendar). ... The bomba (plural bomby) was a special-purpose codebreaking machine designed by Polish cryptanalysts and used to crack the German Enigma machine prior to World War II. A bomba was designed to exploit an obscure but fatal weakness in the Enigma cipher. ... Henryk Zygalski, about 1930. ... The method of perforated sheets was a codebreaking technique used against the Enigma machine (see Cryptanalysis of the Enigma). ...

References

• Władysław Kozaczuk, Enigma: How the German Machine Cipher Was Broken, and How It Was Read by the Allies in World War Two, edited and translated by Christopher Kasparek, Frederick, MD, University Publications of America, 1984, especially pp. 242 and 284-87.