The Poles did it by taking advantage of the German operating practice of repeating the keys to the message twice. In this way, they knew that the 1st and 4th letters of message must be the same, as well as the 2nd and 5th and the 3rd and 6th. After setting up a series of equations, the Poles were still unable to crack the system…..until a German defector delivered several months worth of daily keys. This allow the poles to fill in some of the unknowns and solve the equations to determine the wiring of the rotors. However, the beauty of the rotor systems was that even if the rotor wiring was found, the starting positions for the daily key had 17576 options. The poles eventually created small machines to automate the process of finding the daily key. The system worked by testing a presumed plaintext as being the possible ciphertext. Often times German messages would begin in similar ways, such as their equivilent of "" or "". The Poles built machines to automate the process. These machines were called 'bombes', the Polish word for bomb, presumably because they made loud ticking noises as they worked.

The Polish 'bombes' were effective until the Germans added two more rotors to their system for a total of five. The number of possible keys jumped from 17576 to 11881376 keys. The Polish did not have enough resources to mount an attack on such a system, and instead gave their information, methods and results to France and Britan hoping that they might be able to make use of it. France could not, but the British took advantage of the situation and incorporated the Polish research into their own efforts, which had just begun. The Polish work jump started the British project, and allowed them to create their own bombes.

Alan Turing headed the design and creation of the British bombe for the five rotor system. The machine, about the size of a refrigerator and quite noisy, was brilliant. The device took in the given ciphertext and checked it against the possible plaintext which was supplied by educated guesses. The greetings were so standard that this process wasn't actually very difficult.

Once the machine had the ciphertext and possible plaintext, it would search the text for loops of letters that could only be caused by certain rotor settings. For example,
AJAOERNAEWUAF
OVFNASEWCWFEA

In the above ciphertext/plaintext, the bolded letters show a loop of letters, which in this case begin and end in 'A'. Turing's bombe utilized and loops that were present in the text to help find the rotor settings which could produce the results in the text.

For a far more detailed and indepth discussion of the mechanics within the Turing Machine, you should definitely check out this page.

Well, now that you have a decent idea of the fundamentals behind Rotor systems, we're offering several challenges…

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