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The Enigma

In 1974, the British government permitted the disclosure of the story of the decipherment of the German Enigma cipher machine in World War II. That the Enigma had been broken by the Allies in World War II, however, was not in fact secret up until that time; the account of the capture of the German U-505 submarine in David Kahn's book The Codebreakers from 1967 notes not only that a German cipher machine was captured along with its monthly keys, but that messages on machines of this type were already being read, "with the help of a mass of machinery that filled two buildings". Also, the book "The Broken Seal" by Ladislas Farago referred to a meeting between British and U.S. representatives to discuss a swap of American information on PURPLE for British information on the Enigma (the Americans were generous, but went away empty-handed at the time, but Britain very shortly thereafter relented, as later revealed). But only after 1974 did the details of this cryptanalytic feat emerge. Despite some continued secrecy, it can fairly be said that the cryptanalysis of the Enigma is the only case in which not merely the story of an isolated cryptanalytic success, but instead the ongoing saga of coping with changes in a cipher system, has become public.

Because of the intense concern in the United States about whether or not the Japanese bombing of Pearl Harbor could somehow have been prevented, it was officially revealed quite shortly after the war that cryptanalysts working for the U. S. Government and Armed Forces had solved both Japanese codes and Japanese ciphers, including the cipher produced by the so-called "PURPLE machine".

Had this not been the case, perhaps this would have been kept secret for the same amount of time as the British success in cracking the cipher of the Enigma machine, as a result of the normal reticence of nations concerning matters relating to an activity of such high sensitivity.

As well, given the role of Polish nationals in the early part of the Enigma story, a genuine concern to avoid any of them still residing in Poland being summoned for, at the least, debriefing, may well have been a consideration. As to the sale of used Engimas, I would think that the rule of caveat emptor, rather than any imputation of fraud, would be applicable.

Starting with the commercial Enigma C, the Enigma differed from other rotor machines (although, later, the British Typex and a commercial machine from Ottico Maccina Italiana were based on it) in that the electrical signal for a plaintext letter did not just go in one end of the rotor stack and out the other, but also was sent back to go through the rotors the other way by a reflecting rotor.

This strengthened the cipher in some ways, but also gave it important weaknesses. And it also meant that quite a number of unique cryptanalytic techniques were developed for the Enigma which were specific to it. In comparison, CORAL, although a more difficult target, would still be approached with almost the same techniques as would be used against a Hebern rotor machine, with the exception that the unrelated nature of the alphabets provided by a stepping switch increased the amount of text required for applying those techniques.

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