Colossus Cracks Codes Once More
By Mark Ward
Technology Correspondent, BBC News Website
Thursday, 15 November 2007

For the first time in more than 60 years a Colossus computer is cracking codes at Bletchley Park.
The machine is being put through its paces to mark the end of a project to rebuild the pioneering computer. It is being used to crack messages enciphered using the same system employed by the German high command during World War II.  The Colossus is pitted against modern PC technology which will also try to read the scrambled messages.


Colossus is widely recognised as being one of the first recognisably modern digital computers and was developed to read messages sent by the German commanders during the closing years of WWII. It was one of the first ever programmable computers and featured more than 2,000 valves and was the size of a small lorry (truck).

Colossus in operation during wartime. (Photo via BBC News)

The re-built Colossus will be put to work on intercepted radio messages transmitted by radio amateurs in Paderborn, Germany that have been scrambled using a Lorenz SZ42 machine - as used by the German high command in wartime. German participants in the code-cracking challenge will transmit three enciphered messages - one hard, one very hard and one ultra hard.

Speaking to the BBC, Andy Clark, one of the founders of the Trust for the National Museum of Computing, said radio problems had stopped the challenge getting under way on time. "The radio path has not been particularly good between Germany and here," he said. "We are at a bad point in the sunspot cycle."  Signals had improved throughout the day, he added, and he hoped to get 100% of the ciphertext - the code - through soon.

The Colossus machine will be pitted against modern computer technology that will also be used to decipher and read the transmitted messages. Tony Sale, who led the 14-year Colossus re-build project, said it was not clear whether the wartime technology or a modern PC would be faster at cracking the codes.

The rebuilt Colossus - what a work of art! (Photo via BBC News)
"A virtual Colossus written to run on a Pentium 2 laptop takes about the same time to break a cipher as Colossus does," he said. It was so fast, he said, because it was a single purpose processor rather than one put to many general purposes like modern desktop computers. Mr Sale it could be Friday before the teams find out if they have managed to read the enciphered messages correctly. Re-building the pioneering machine took so long because all 10 Colossus machines were broken up after the war in a bid to keep their workings secret. When he started the re-build all Mr Sale had to work with were a few photographs of the machine.

In its heyday Colossus could break messages in a matter of hours and, said Mr Sale, proved its worth time and time again by revealing the details of Germany's battle plans. "It was extremely important in the build up to D-Day," said Mr Sale. "It revealed troop movements, the state of supplies, state of ammunition, numbers of dead soldiers - vitally important information for the whole of the second part of the war." This, and the other information revealed by the code-cracking effort at Bletchley, helped to shorten the war by at least 18 months, said Mr Sale.

The Cipher Challenge is also being used to mark the start of a major fund-raising drive for the fledgling National Museum of Computing. The Museum will be based at Bletchley and Colossus will form the centre-piece of its exhibits.

Colossus has a place in the history of computing not just because of the techniques used in its construction. Many of those that helped build it, in particular Tommy Flowers and Tommy Kilburn, went on to do work that directly led to the computers in use today. The Museum said it needed to raise about £6m to safeguard the future of the historic computers it has collected.

colossus03_bbcnews.jpg colossus04_bbcnews.jpg
Closeup of indicator panel and plug panel. Briefly, the first Colossus had contained 1500 tubes; the production machines needed 2400 tubes because of their increased processing power and facilities, together with 12 large rotary switches, about 800 relays, and an IBM electric typewriter to print the output. (Photo via BBC News)

The high speed paper tape reader could run at 5000 characters per second and generate it's own clock pulse thus the output was unaffected by speed changes. Here, the three tapes on the left are running. (Photo by Bruce MacMillan) 

John Alexander, a crypto machine aficionado who was at the event, files this report.

I was down at BP yesterday.  A friend wanted to visit for the first time. BBC Radio 4 had transmitted a piece about the challenge at 08:56.  Just every now and then a piece captures the real heart of the event. At BP were the BBC, the British Forces Broadcasting Service - and others. There was a real buzz about the place and the H Block exhibits really come into their own.  Receivers were crackling, undulators were undulating and recording the incoming signals, Heath-Robinson and Tunny looked on.

Colossus was looking Colossal and nicely on-form. Tony and Cliff of the build team were with Colossus, answering questions of reporters and visitors to H Block. Information that the NSA and GCHQ would 'have a go too' really warmed the cockles and made us smile.

The weather was great  (cold and crisp, blue skies) but not so good for propagating radio signals from Paderborn.  The Milton Keynes Amateur Radio club were on site (they have a permanent station at BP) and anyone who wished, could see the signals being received. Fortunately, signals were repeated at regular intervals  on various bands.

You might have guessed - I really enjoyed being there.

A comment from someone on the Rebuild Team. "Further to this, we are absolutely delighted to announce that the Colossus Rebuild Team cracked the code at 1315 hrs today after a  running time of around 3 hours and 35 minutes. We would also like to warmly congratulate the German amateur enthusiast who beat Colossus to it!"

This story, written by D'ARCY DORAN, Associated Press Writer, on Nov 17/07 provides more details about the German codebreaker.

"LONDON - A rebuilt World War II code-cracking computer developed to intercept Nazi messages lost to a desktop computer Friday in a contest to decipher an encrypted radio message.

The challenge marked the first time the Colossus machine had been used since former Prime Minister Winston Churchill ordered models of the top secret computer destroyed, according to Britain's National Museum of Computing, which organized the contest.
Churchill had feared Britain's national security would be threatened if the state of the art computer's technical details ever leaked out.

However, not only was Colossus beaten by a home computer, but by one in Germany.
Bonn-based software engineer Joachim Schueth deciphered the message, which was encrypted by a Nazi-era Lorenz cipher machine and transmitted by radio from Paderborn, Germany. It took him 1.5 minutes.  He used ham radio equipment and a computer program he wrote especially for the challenge.

Schueth paid tribute to Colossus and those who used it during WWII at the Bletchley Park code-breaking center, outside London, saying their work was important to Germans because "it helped to shorten the lifetime of the Nazi dictatorship."But Colossus, the world's first programable computer, was no match for its electronic descendants, he said.
"Putting Colossus in a competition with modern computers may be a bit unfair," Schueth wrote on his Web site.

Colossus eventually completed the challenge in three hours and 35 minutes, after overcoming difficulties intercepting the distant radio signal and repairing a blown valve.
"We've lost appreciation of just how hard it was to intercept signals, interpret them and put them on Colossus and run them," said Andy Clark, director of the Bletchley Park-based computing museum. "The past two days have brought into sharp focus just how hard they had to work," he said.

Experts spent 14 years rebuilding the Colossus using stolen design plans and by gleaning information from those who helped create the original. Ten Mark II Colossus machines enabled code breakers at Bletchley to decipher top-secret communications sent by the Nazi high command.

The rebuilt computer will continue to operate as the museum's centerpiece, Clark said."

The message for the challenge was encrypted on a Lorenz SZ-42 cipher machine such as this.  (Photo courtesy Wikipedia)

If there were only photographs to go by, how did the Team know what architecture and components to use in the rebuild ? It was mainly due to favourable circumstances.  The Colossus project had important input from some of the original designers and engineers who constructed it along with some drawings which they had kept since WWII. Among them was Arnold Lynch, who constructed the high-speed reader system.

Tommy Flowers, the chief designer, provided assistance  from 1995 until his passing in 1998. Colossus and had used standard telephone exchange equipment for the design. Lots of this used equipment is still available after it is stripped out of old telephone exchanges. Finally, the rest was worked out by Tony Sale and his team from the National Museum of Computing.

Apparently, one of the original WWII thermionic valves is still fitted and working in Colossus. The team  take great care in slowly warming up the machine to full operating temperature.

Credits and References:

1) BBC Web site
2) Tommy Flowers
3) John Alexander <jalex_uk(at)>
4) Dirk Rijmenants
5) Bruce MacMillan <bruce_macmillan(at)>

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