Метод листов Зыгальского: Взлом немецкой «Энигмы» во Второй мировой войне.

Cryptologic technique used in World War II

The method of Zygalski sheets was a cryptologic technique used by the Polish Cipher Bureau before and during World War II, and during the war also by British cryptologists at Bletchley Park, to decrypt messages enciphered on German Enigma machines. The Zygalski sheet apparatus takes its name from Polish Cipher Bureau mathematician–cryptologist Henryk Zygalski, who invented it about October 1938.

The Cipher Bureau's manual manufacture of the sheets, which for security reasons was done by the mathematician cryptologists themselves, using razor blades, was very time consuming. By 15 December 1938 only a third of the job had been finished. On that date, the Germans introduced rotors IV and V, thus increasing the labor of making the sheets tenfold, since ten times as many sheets were now needed (for the now 60 possible combinations of sequences, in an Enigma machine, of 3 rotors selected from among the now 5). Part of the disclosures involved Zygalski's "perforated sheet" method. The British, at Bletchley Park, near London, England, undertook the production of two complete sets of perforated sheets. The work was done, with the aid of perforators, by a section headed by John R. F. Jeffreys. The sheets were known at Bletchley as Netz (from Netzverfahren, "net method"), though they were later remembered by Gordon Welchman as "Jeffreys sheets"; the latter term, however, referred to another catalog produced by Jeffreys' section. and were couriered by Alan Turing to France shortly thereafter. In May 1940, the Germans once again completely changed the procedure for enciphering message keys (with the exception of a Norwegian network). As a result, Zygalski's sheets were of no use, though the Herivel tip could still be used.