Remembering Colossus Cipher Challenge Pt 1

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On Thursday 15 November 2007, a rebuilt Colossus Mark II was ready to decipher a teleprinter message transmitted by radio from colleagues in the Heinz Nixdorf Museum in Paderborn, Germany, having been encrypted by one of the original Lorenz cipher machines used by the German High Command during the Second World War.

The Paderborn transmissions were to be intercepted at Bletchley Park by Milton Keynes Amateur Radio Society. Other amateur code breakers are also invited to join the challenge to intercept the transmission and to try to beat Colossus in cracking the Lorenz SZ42 encrypted message.

Andy Clark recalls: "The whole exercise showed how how every part of the process had to work flawlessly -- it was a hard problem where people working together really mattered."

"Tony Sale, who had devised the Challenge really really wanted Colossus to win. He thought it was the ideal engine for the job, but he knew that technology had moved on and a concerted effort by a crypto engineer could pip Colossus at the post."

The task for the international team was:

  • Encipher a secret plaintext message in Germany using an original Lorenz SZ42 cipher machine
  • Transmit the ciphertext using amateur radio operators in Germany
  • Intercept the ciphertext at a replica ‘Y’ station in the UK
  • Interpret the ciphertext using an original undulator and transfer that interpreted ciphertext on to paper tape
  • Load the paper tape ciphertext on the Colossus Mark II rebuild in Bletchley Park Block H.
  • Run the Colossus to recover the Lorenz machine wheel settings used to encipher the plaintext
  • Recover the secret plaintext message
  • Validate the result.

The next two days were to attract the world's press attention to that 'irreplaceable place' - Block H.

Here's footage of the arrival of the Lorenz SZ42 at Heinz Nixdorf Museum ten years ago and the setting of the Lorenz wheels -- that Colossus was destined to discover.

Day One began with trustee Andy Clark being interviewed on BBC Radio 4's Today Programme -- no pressure there then!

Meanwhile at the Heinz Nixdorf Museum in Paderborn, the Lorenz SZ42 was working:

To Part 2 >>>

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