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Geek Weekend, Day 1: Bletchley Park

Left to my own devices to the weekend I decided to embark on a Geek Weekend with visits to two places within easy reach of London. Today I visited Bletchley Park which is simply wonderful for any geek out there.

Bletchley Park is where the cryptanalysts of the Second World War worked in great secrecy (including Alan Turing) to break the Nazi German Enigma and Lorenz ciphers. To break them they used a combination of intimate knowledge of language, mathematics and machines.

Here's a Nazi German Enigma machine:



And here's a look inside one of the rotors inside an Enigma machine to see the wiring:



Two of the code breaking machines have been reconstructed. One is the Turing Bombe, an electromechanical machine made to break the Enigma cipher. Here's a look at the wiring in the back of the Bombe:



The other machine is the Colossus, a binary computer built to decipher Lorenz. Enigma is far more famous than Lorenz, but I have a soft spot for the Lorenz code because of its close relationship to modern cryptography. Here's a Lorenz machine:



While I was there I signed a large stack of copies of my book, The Geek Atlas. If you are at Bletchley Park and pop into the shop you'll be able to buy a signed copy if that's your thing. Of course, Bletchley Park, Enigma, Lorenz and the National Museum of Computing (also on site) are covered.

50p from every copy of The Geek Atlas goes to Bletchley Park (if the book is bought in the UK) and so the folks at Bletchley treated me to a special geek moment: a chance to meet Tony Sale who worked at MI-5 and reconstructed the Lorenz breaking machine Colossus. He took me round the back of the machine, and past the No Admittance sign to see it in operation. A geek treat if ever there was one.

The Lorenz code is essentially binary. Letters were transmitted using the Baudot Code which is a five-bit code. To encrypt the Lorenz machine created a pseudo-random sequence of Baudot codes and then XORed them with the message to be transmitted. If both transmitting and receiving machines generated the same pseudo-random sequence then the nice property of XOR that if you perform the same operation twice you get back to where you started. Thus XORing once with the pseudo-random sequence gave you the ciphertext to be transmitted, XORing again gave you back the original message.

Breaking this binary code was achieved with a binary computer. After giving me a behind-the-scenes look at Colossus, Tony Sale stood for a portrait in front of the machine:



And behind the machine is where the valve-action is:



Standing and see the Turing Bombe, staring into Turing's office in Hut 8, being taken around the back of Colossus by the man who put it back together, and getting to see more Enigmas, Lorenzs and Typexs than anyone could ask for made it a real treat.

The National Museum of Computing is Britain's answer to the wonderful Computer History Museum in Mountain View, CA. It contains many machines from the mainframe through the 8-bit era of British computing. All the machines are working or being restored. If you've never seen core memory, massive hard disk packs the size of washing machines, or just Commodore PET it's worth visiting (and it's right next door to Colossus).

Lastly, it's worth knowing that the National Museum of Computing despite being part of the ticket price to Bletchley Park actually receives no money from them. Please consider either donating money directly to them (I gladly emptied my pockets of change) or buying something in their shop.

And tomorrow it's a step back into the 19th century with a special visit to a place important in the life of Isambard Kingdom Brunel.

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