Monday, October 30, 2006

Bombe Rebuild Project

The Turing Bombe was a machine that truly turned the tide of war. For many years it was top secret and after 60 years a team, lead by John Harper, finally completed the rebuild of this wonderful machine. Last month, for the first time since the end of the war, a full demonstration of a working Bombe took place in Bletchley Park.

The Turing Bombe was designed by Alan Turing and Gordon Welchman to break into the message traffic, encrypted with the notorious German Enigma cipher machine. The Bombe was an electromechanical device that searched for the enigma settings for a given piece of plain and cipher text. When an Enigma message was intercepted, codebreakers had to search for cribs. These cribs were presumed pieces of plain text within the encrypted message. This could be "An Der Oberbefehlshaber", "An Gruppe" or "Es Lebe Den Fuhrer" or any other standardized piece of text. Once a crib was located (there were some techniques for that) the associations between the letters of the ciphertext and their plain version were entered in the Bombe. The Bombe, which contains a large number of drums, each replicating the rotors of the Enigma, ran through all possible settings to find the key settings that belong to the given pieces of cipher and plain text. Once these settings were found all messages, encrypted with these setting, could be deciphered.

More information on the rebuild of the Turing Bombe can be found on John Harpers website, with some nice pictures of the Bombe project. For more details on how the Turing Bombe worked you should visit Graham Ellsbury's Bombe pages. To see the actual Bombe you will have to visit Bletchley Park, which also has a great Enigma And Friend exhibit, and is really worth while the trip.

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