Editing Bomba (cryptography) (section)

==History==
[[File:Enigma-plugboard.jpg|thumb|Enigma's plugboard, with two cables connected (ten were used during [[World War II]]). This enhancement greatly increased the system's security.]]
{{EnigmaSeries}}

Using the knowledge that the first three letters of a message were the same as the second three, Polish mathematician–[[cryptologist]] [[Marian Rejewski]] was able to determine the internal wiring of the Enigma machine and thus to reconstruct the logical structure of the device. Only general traits of the machine were suspected, from the example of the commercial Enigma variant, which the Germans were known to have been using for diplomatic communications. The military versions were sufficiently different to present an entirely new problem. Having done that much, it was still necessary to check each of the potential daily keys to break an encrypted message (i.e., a "ciphertext"). With many thousands of such possible keys, and with the growing complexity of the Enigma machine and its keying procedures, this was becoming an increasingly daunting task.

In order to mechanize and speed up the process, Rejewski, a civilian mathematician working at the Polish General Staff's Cipher Bureau in [[Warsaw]], invented the ''"bomba kryptologiczna"'' (cryptologic bomb), probably in October 1938. Each bomb (six were built in Warsaw for the Cipher Bureau before September 1939) essentially constituted an electrically powered aggregate of six Enigmas and took the place of some one hundred workers.<ref>Marian Rejewski, "Appendix E: The Mathematical Solution of the Enigma Cipher" in {{harvp|Kozaczuk|1984|p=290}}.</ref> 

The bomb method was based, like the Poles' earlier [["grill" method]], on the fact that the plug connections in the commutator ("plugboard") did not change all the letters. But while the grill method required unchanged ''pairs'' of letters, the bomb method required only unchanged letters. Hence it could be applied even though the number of plug connections in this period was between five and eight. In mid-November 1938, the bombs were ready, and the reconstructing of daily keys now took about two hours.<ref>Marian Rejewski, "Appendix C: Summary of Our Methods for Reconstructing ENIGMA and Reconstructing Daily Keys, and of German Efforts to Frustrate Those Methods in {{harvp|Kozaczuk|1984|p=242}}.</ref>

Up to July 25, 1939, the Poles had been breaking Enigma messages for over six and a half years without telling their [[France|French]] and [[United Kingdom|British]] [[Allies of World War II|allies]]. On December 15, 1938, two new rotors, IV and V, were introduced (three of the now five rotors being selected for use in the machine at a time). As Rejewski wrote in a 1979 critique of appendix 1, volume 1 (1979), of the official history of ''British Intelligence in the Second World War'',  "we quickly found the [wirings] within the [new rotors], but [their] introduction [...] raised the number of possible sequences of drums from 6 to 60 [...] and hence also raised tenfold the work of finding the keys. Thus the change was not qualitative but quantitative. We would have had to markedly increase the personnel to operate the bombs, to produce the [[perforated sheets]] (60 series of 26 sheets each were now needed, whereas up to the meeting on July 25, 1939, we had only two such series ready) and to manipulate the sheets."<ref name = Rejewski80>{{cite journal |author=Marian Rejewski |title=Remarks on Appendix 1 to ''British Intelligence in the Second World War'' by F. H. Hinsley |translator=[[Christopher Kasparek]] |journal=[[Cryptologia]] |volume=6 |number=1 |date=January 1982 |pages=75–83, etc. p. 80}}</ref>

[[Harry Hinsley]] suggested in ''British Intelligence in the Second World War'' that the Poles decided to share their Enigma-breaking techniques and equipment with the French and British in July 1939 because they had encountered insuperable technical difficulties. Rejewski rejected this:  "No, it was not [cryptologic] difficulties [...] that prompted us to work with the British and French, but only the deteriorating political situation. If we had had no difficulties at all we would still, or even the more so, have shared our achievements with our allies as [[Polish contribution to World War II|our contribution to the struggle against Germany]]."<ref name = Rejewski80/>