6.2s discover cipher secrets at Bletchley Park

On Tuesday 26 February, the 6.2 Maths students took a once in a lifetime trip to Bletchley Park where we discovered the secrets of how the British cracked the German ciphers during the Second World War, most notably the Enigma cipher. We started with a fascinating workshop where we learnt how the Enigma cipher is encoded and the extraordinarily number of different ways the machine could be set up. Each day the machine would be set up in a different way and so messages were encrypted differently depending on the day on which they were encrypted. This made the cipher extremely hard to decrypt without the German code book, which had instructions on how the machine should be set up on each day. The British made several attempts to capture these code books but many of them were unsuccessful. The Germans were so confident that their cipher was impossible to crack that they broadcasted their messages on the radio, which allowed the British to intercept large numbers of encrypted messages, thus making the cipher easier to crack. In the afternoon we were shown the machines that were designed and built by the team working at Bletchley Park to decrypt the ciphers. The most notable of these ingenious machines was the Bombe, (there were many dozens of them built) which was designed to help decrypt the intercepted Enigma codes by determining the settings of the Enigma machines for a given message. Once the settings were known the text could be decrypted by typing the message into an Enigma machine programmed with the correct settings. The Lorenz cipher was much more sophisticated than the Enigma cipher and was used to encrypt communication within the German high command. This cipher was much harder to crack than the Enigma because the British did not know the design of the machine that encrypted it. It would have been impossible to crack were it not for a German communications officer repeating a single message, a very serious error. The second time the message was sent it was abbreviated (the officer was lazy) so the message had the same meaning but the text was slightly different.  This enabled the British to determine the mechanism behind the Lorenz cipher and so they were able to design a machine to help them decrypt it. The machine they designed was called the Tunny machine. If the initial settings of the Lorenz machine were known then the encrypted message could be typed into the Tunny machine and the message would come out in plain text. However it was very difficult to determine the initial settings of the machine and so another machine called Colossus was designed to deduce these initial settings.

By Maddy Green and Sam Wilkinson (6.2)

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Bedales School is one of the UK’s top independent private co-education boarding schools. Bedales comprises three schools situated in Steep, near Petersfield, Hampshire: Dunannie (ages 3–8), Dunhurst (ages 8–13) and Bedales itself (ages 13–18). Established in 1893 Bedales School puts emphasis on the Arts, Sciences, voluntary service, pastoral care, and listening to students’ views. Bedales is acclaimed for its drama, theatre, art and music. The Headmaster is Keith Budge.

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