The National Museum of Computing challenges public to beat Colossus

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Allies’ secret weapon at Bletchley cracks German codes again

The world’s first programmable digital computer, developed at Bletchley Park to crack encoded German messages during World War II, returns to action on 15 November 2007 to mark the launch of the first part of the emerging National Museum of Computing.

This time the encrypted transmissions will be entirely peaceful in content and celebrate the completion of the successful rebuild of Colossus and the start of a major fund-raising drive for the fledgling National Museum of Computing.

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

The Paderborn transmissions will be intercepted at Bletchley Park by two groups of amateur codebreakers, one using modern equipment and PCs and the other using World War II technology. Other amateur code breakers are also invited to join the challenge to intercept the transmission and to try to beat Colossus in cracking the 1938 Lorenz SZ42 encrypted message.

The recreated Colossus is on public display at The National Museum of Computing at Bletchley Park, Buckinghamshire, following a 14-year rebuilding project led by Tony Sale, a founder of the emerging Museum.

The trustees of the Museum, which is opening in stages, plan to secure £6 million in investment to fully establish and run the facility. The British Computing Society has already donated £75,000 to help start the museum.

The rebuilt Colossus is now in Bletchley Park’s Block H, the first purpose-built computer centre, where the machine operated during the war.

Colossus provided the Allies with crucial information on enemy plans. The ten Mark II machines were instrumental in shortening the war by several months and leading to thousands of lives being saved.

They were so fast that a mid-range modern PC programmed today to perform a similar code-breaking task would take as long as Colossus to achieve a result.

Tony Sale said: “The rebuilt Colossus is on public display as part of the emerging National Museum of Computing. Colossus marks the beginning of the modern age of computing – a heritage that we are planning to preserve by raising £6 million to establish a world-class facility at Bletchley Park.

“Witnessing Colossus Mark II in action is a chance to relive and admire the historic break-through made by Bletchley Park code breakers during World War II. We’re inviting members of the public to try to crack the code before Colossus, which should prove enormous fun.”

He added: “Such was the secrecy surrounding Bletchley Park in those days that what the machines did remained under wraps for many years. Today, however, we believe the legacy of the code breakers, who paved the way for modern-day computing, should be seen, treasured and admired by everyone.”

Notes to editors

Cipher Challenge

On 15 and 16 November 2007, the public are invited to intercept and decode Lorenz code transmitted from National Museum of Computing colleagues in Paderborn, Germany.

Members of the public may participate in one of three challenges of varying complexity.

The international team will:

  • 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 2 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.

History of Colossus

German teleprinter signals encrypted by Lorenz machines were first heard in Britain by police officers on the south coast listening for possible spy transmissions in 1940.

Brigadier John Tiltman, one of the top code breakers at Bletchley Park, was informed. In August 1941, a procedural error by German operators enabled Tiltman to work out the pattern of obscuring characters Lorenz was adding to messages to encipher them.

Fellow code breaker Bill Tutte began working on the case. Two months later Bletchley Park researchers worked out the complete logical structure of the cipher machine, which we now know as Lorenz.

The only problem was that messages still took four to six weeks to decrypt, by which time information could be stale and of little use. Max Newman, a mathematician at Bletchley Park, believed certain aspects of the decryption process could be automated. By December 1943, Tommy Flowers, a Post Office electronics engineer, had designed and built Colossus Mark I to Newman’s requirements.

The Mark I began operating in January 1944, succeeded in June of that year by the Mark II. Ten Mark II machines were built.

Colossus enabled experts to unravel encoded communications in a matter of hours rather than weeks. This provided Field Marshall Bernard Montgomery, commander of the British Army, and General Dwight Eisenhower, commander of the Allied forces in Europe, with crucial intelligence on what enemy armed forces were plotting.

As a direct result of Colossus, the war was shortened by several months and thousands of lives saved. By the end of the war, 63 million characters of high-grade German messages had been decrypted by the 550 people working on the Colossi at Bletchley Park.

Rebuilding Colossus Mark II

Tony Sale, founder of the Codes and Ciphers Heritage Trust, began a project to rebuild Colossus in 1993 after snippets of information emerged about the machines in the 1970s and 80s gave him the idea.

With eight photographs of Colossus taken in 1945, the ambitious project was under way. Circuit diagrams, kept illegally by engineers who worked on the original computer, were also obtained.

Mr Sale managed to track down Dr Arnold Lynch who was involved in the original project, designing the optical paper tape reader system in 1942, to glean further information.

On November 15 2007, a rebuilt fully-functioning Colossus Mark II was unveiled to the public at the emerging National Museum of Computing, Bletchley Park. See

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