German pips Bletchley’s Colossus in cracking battle

A man in Bonn has cracked a message encrypted with wartime Germany's most-secure Lorenz equipment within hours of its release on 15 November, beating a rebuilt Colossus machine within Britain's Bletchley Park code-breaking centre -which was delayed in its task by solar activity disrupting radio signals.

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A man in Bonn has cracked a message encrypted with wartime Germany's most-secure Lorenz equipment within hours of its release on 15 November, beating a rebuilt Colossus machine within Britain's Bletchley Park code-breaking centre -which was delayed in its task by solar activity disrupting radio signals.

It sounds like several twists in the plot of a Second World War thriller, but Joachim Schüth, who wrote special software to meet the challenge, will be invited to visit Bletchley to receive a prize from the nascent National Museum of Computing.

"We really want to congratulate him," said Andy Clark, a director and trustee of the museum. Schüth has cracked the hardest of three signals transmitted yesterday by radio enthusiasts in Germany from 11am, although Bletchley Park only managed to receive them at 5.40pm.

Bletchley Park, the first base of the UK's signal interception and decryption unit the Government Communications Headquarters (GCHQ), is best-known for cracking Nazi Germany's widely-used secure communications equipment, the Enigma machine. This allowed Britain to read much of its wartime enemy's encrypted traffic, and Bletchley is credited with shortening the Second World War by months or even years.

The Enigma traffic was broken by mechanical computers known as bombes, and has been commemorated by books including Robert Harris' novel Enigma, which was made into a film. But the Colossus, which broke the top-secret Nazi Lorenz traffic, is less famous. Clark said this is partly because Britain told its wartime allies, including the Soviet Union, about breaking Enigma, but not about breaking Lorenz, and Colossus machines stayed in service after the end of the Second World War. The Enigma-breaking story was first told in Poland in 1967, while that of Colossus only emerged during the 1970s.

It is likely to become rather better known, as a rebuilt Colossus machine started work on the Lorenz-encoded message just before 9am on 16 November. Tony Sale, a computer expert and former employee of the UK security service MI5, started campaigning for Bletchley Park to be saved from demolition in 1991. He spoke to Infosecurity while supervising the operation of a fully-working Colossus machine able to tackle Lorenz - which is now a listed object in a listed building, representing the success of his campaign.

Sale said it has been possible to rebuild a Colossus as the design used standard components used in Post Office telephone exchanges: Tommy Flowers, who worked alongside Alan Turing in designing the Colossus, worked for the Post Office before and after the war.

Due to British Telecom's programme of replacing these mechanical exchanges over recent decades, plenty of these components were available second-hand. A few components, such as the "bedstead" through which the loop of paper holding the encoded message runs, were made from scratch.

But the machine also includes nine original components, Sale added: eight photo-cells and a mains transformer. "When the engineers were dismantling Colossi at the end of the war, photo-cells were a very nice thing to put in your pocket," he said, as these are two inches high and 1.5 inches in diameter. However, the rebuilt machine normally uses modern silicon photo diodes, as the older photo-cells are fragile and need resting after prolonged use. The mains transformer was also retained by an engineer, as were some designs for the equipment, although original designs were burnt in 1960.

The Colossus machine does not break Lorenz messages, but attempts to find the wheel-settings - mechanical encryption keys - used by the Germans (in this case, volunteers from Heinz Nixdorf Museum Forum in Paderborn). It does so by repeatedly running the paper loop into which the message is punched through the machine, trying different positions of a pair of Lorenz machine wheels one after another in a brute-force attack.

Sale said the operator has to mark the start and end positions of the message on the tape, then the Colossus reports likely matches, using a scoring process. "Colossus does not 'know' when it has a good thing," said Sale, only when a match looks more likely. The operator then has to use the possible wheel positions to attempt to decode the message using a Tunny machine - the British named German war-time codes after fish. "If you have got it right, out comes German," said Sale.

Andy Clark said that although the Colossus processes 5000 characters a second (5 kilohertz), and employs extensive parallel processing, he assumes that the fastest machines doing this kind of code-breaking are capable of working in Terahertz, processing trillions of characters a second.

GCHQ, which moved to Cheltenham in 1952, also invented public-key encryption in 1973 - although it did not make the work of its employee James Ellis public, leaving others to make the same discovery independently.

Its press office said that GCHQ had no involvement in the work beyond loaning equipment including a Lorenz machine to the museum. "We applaud and support the ingenuity in rebuilding Colossus - a fantastic piece of work," said a spokesperson.

This article first appeared on the website of Infosecurity magazine.



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