| Break an Enigma Key with Bombe |
IntroductionAs early as the spring of 1940, cryptologists at Hut 6 assumed, without any certainty, the existence of key rules. They began to search the broken keys for any building rules followed by the enemy. However, to be certain, they had to accumulate many keys. The rules were used as soon as they were discovered. They made it possible to significantly reduce the tests carried out in conjunction with manual methods and when using the Bombe. The most important key rulesNon-clashing ruleOn any two consecutive days in the same month, the same wheel could not be used in the same place. By this rule alone, if any one day was out, the wheel order for the next day was automatically reduced to 32 instead of 60.Non-repeating ruleWithin a month, the same wheel order was not used twice. This rule was never quite so absolute.Clarkian ruleThis rule held on Red and Light Blue from August to November 1941 and was named after its discover, L.E. Clarke. The rule states that, in the same column, no wheel is followed by a consecutive wheel: 5 and 1 are not, however, regarded as consecutive.An example of using key RulesSuppose we want to test menus for the red network on February 14 and have broken all the previous days. It is possible to drastically reduce the number of Wheel Orders to be tested. Walzenlage (WO) for the beginning of February 1941 1 251 2 534 3 152 4 531 5 354 6 532 7 154 8 231 9 524 10 451 11 124 12 512 13 234Deductions:
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