Bletchley Park

We spent Saturday at Bletchley Park. That is a little town north of London where Alan Turing worked trying to crack the code that the Germans were using in World War II. At the peak there were apparently 10.000 people working there, also building a magnificent single-purpose computer, the Colossus, to crack open the one-time pad generated by the Lorenz Machine for use be the German High Command.

Saturdays are wonderful days, as there are volunteers out there enthusiastically explaining how the machines work. The only down side is that the National Computer Science Museum and Bletchley Park are on the same grounds, but they don't cooperate, so you have to pay two entrance fees if you want to see both machines running. But it is worth it! And if you are heading up by train, there's a 2-for-1 coupon that you can print out in advance, that saves 15 pounds.

It was nice to see a lot of material in person and to be able to photograph it. There were live demonstrations of a rebuilt Bombe and the rebuilt Colossus. All machines and material were to have been destroyed after the war, as this was a top-secret operation, but luckily there were a few photos and diagrams, and there were still some of the engineers alive as groups started re-producing the parts.

The Colossus was primarily built out of standard telephone exchange parts, as the telephone engineers built it. When British Telecom was upgrading their analog parts to digital, one of the members of the rebuild team drove around with a truck, picking up all the analogue parts (especially valves) he could. The presenter requested that everyone have a look in their garage and attic to see if they happened to have a few lying around, as they are too expensive to produce any more. They consist of hand-blown glass with metal and plastic parts. I wonder if there will ever be a 3D printer for retro parts.

I must have taken 100 pictures, far too many to post here. I guess I'll have to teach cryptography again only in order to use them - and in order to explain how the codes were cracked. The "unbreakable" Lorenz cipher was broken when a soldier re-used the same one-time pad to resend a message that was slightly different - with abbreviations. And the Enigma was brute-forced after some lateral thinking showed that there was a flaw - a character could never be mapped to itself. And since the Germans love wordy, standard terminology, and had a tendency to send messages at the exact same time every day (like the Wettervorhersage, the weather report, or regular reports that nothing had happened worth reporting - Keine besondere Vorkommnisse) so the engineers could compare the intercepted code with typical words that they expected to be in the text, and were thus able to rule out quite a number of cases. With the Bombe they then brute-forced the rest of the possibilities, using a machine called the Type-X that you could set a possible key and type in the message and see if it fell out in plain text. What a disappointment that must have been to spend all day decoding and then to learn that the Kleiderpauschale had been raised by one Reichsmark or something equally boring.

It was a fascinating day, I could have spent lots more time AND bought one of everything in the gift shop. But I'm flying and already close to the weight limit, so I just purchased some postcards and a DVD.

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