Tunny, Colossus and Ada: Keeping an Open Mind

Joachim Schüeth is the winner of National Museum of Computing's Colossus Cipher Challenge. Using his laptop, Schüeth unravelled a code transmitted from the Heinz Nixdorf Museum in Germany, from a Lorenz SZ42 Cipher machine, used by the German High Command to relay secret messages during the World War II.

Speaking in front of Colossus at Bletchley Park, Schüeth said: "It was unfair because I was using a modern PC, while Colossus was created more than 60 years ago. It really is astonishing and humbling that the world's first programmable, digital computer was created in the 1940s. Without those Bletchley Park pioneers, I would be out of a job."

On November 15, 2007 I took my laptop to the nearby radio shack of the amateur radio club of Bonn. Being initially hampered by poor radio propagation and noise, I could finally record and decrypt several of the transmitted Cipher Challenges. Running on a 1.4 GHz CPU, the Ada program that does the code breaking found the correct settings of all 12 key wheels of the SZ42 within 46 seconds. This was way faster than Colossus, which completed the same task within about three and a half hours. Colossus reads the ciphertext input from a punched paper tape looping at a speed of 5000 characters per second. On my computer, I measured the equivalent speed to be about 1.2 million characters per second, which is 240 times faster. When scaling the CPU frequency by this factor, Colossus is equivalent to a 5.8-MHz computer. Measured by Moore's law, this is an enormous speed for a machine built more than six decades ago.


It wasn't the code breakers at Bletchley who built Colossus, it was Dr Tommy Flowers of the GPO research labs at Dollis Hill. The world's first programmable, digital computer was built by the Post Office! Don't listen to any Americans who try to tell you anything different.
Wasn't Colossus built from BT 'spares'?

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