Computer History Decrypted

New book publish a series of essays by a number of original Bletchley Park code breakers

7 March 2008

In January, an amateur code breaker received an award for taking just 46 seconds to unravel messages that were enciphered by the same type of machine used by the German High Command during World War II. The award went to Joachim Schüth, a German software engineer who had won the British National Museum of Computing’s Cipher Challenge the previous November. Not only had Schüth bested a host of other code breakers like himself, he beat the Colossus Mark II, a room-size WWII-era computer originally used by British code breakers to reveal Germany’s tactical plans.

Schüth used a laptop with a clock speed of 1.4 gigahertz, running his own deciphering software. It processed the encrypted text at a rate of 1.2 million characters per second. The rebuilt Colossus, one of 10 British code-breaking behemoths that were revealing German secrets by the end of WWII, handled 5000 characters per second and decoded messages in 3 hours and 15 minutes.

“If you scale the CPU frequency, you get an equivalent clock speed of 5.8 megahertz for Colossus,” says Schüth. “That is a remarkable speed for a computer built in 1944.” Colossus was so advanced that even as late as the 1980s, beating it with a modern computer would not have been a sure thing.

RACE TO DECODE The Cipher Challenge pitted the rebuilt Colossus against radio amateurs worldwide in a test to see who could be the first to receive and decode three enciphered and transmitted messages. While Schüth’s victory demonstrated just how far computing has come in the last decades, the objective of the Cipher Challenge was to highlight a major historical oversight. “For far too long the Americans have got away with the myth that the Eniac was the first large-scale electronic digital calculator in the world,” says Anthony E. Sale, a founder of the National Museum of Computing who led the effort to bring the last remaining Colossus machine back to life. “They got away with it because Colossus was kept secret until the 1970s.” 

Though many believe that the Eniac computer, powered on in 1946 at the University of Pennsylvania in Philadelphia, was the world’s first programmable digital electronic computer, the Colossus machine holds that distinction. When it went into service at Bletchley Park in Buckinghamshire, U.K., in February 1944, the Colossus I, with its 1500 vacuum tubes, allowed British cryptologists to break an entire day’s communication between Berlin and German field commanders in a matter of hours.

Although a few papers hinting at Bletchley Park’s significance appeared in the 1970s, it wasn’t until 2000, when information surrounding Colossus was declassified, that Britain’s role in the history of computing became clearer. And it took six more years before the reminiscences of the code breakers themselves were published.

“The original Bletchley Park code breakers were eager to tell their stories,” says Jack Copeland, who sought them out for his Colossus: The Secrets of Bletchley Park's Codebreaking Computers (2006, Oxford University Press). The book is a series of essays by a number of original “Bletchley Parkers.” A review of the book appeared in the IEEE History Center’s November 2007 newsletter

MUM’S THE WORD “Though [the code breakers] were very approachable, before the classification was lifted, they were wary of even getting on the subject for fear that—even six decades after the fact—they might say something that would land them in trouble,” says Copeland, an IEEE affiliate member. A three-man cryptology team at Bletchley Park had by July 1942 begun to break the ever-changing German Enigma codes applied to teletype communications and remove obscuring characters by hand. But by the end of 1943, the German military began to rely on a more complex coding system built into its Lorenz SZ42 encryption machine. The Germans’ confidence in this new machine led them to send even more messages than before. The sheer volume was so great, recalls Jerry Roberts, a member of the Bletchley Park team, that it became impossible to break the encryption and figure out the messages while they were still relevant. More computers were needed, and “by the end of the war, nine more Colossi had been built. And we were breaking about 95 percent of German traffic,” says Roberts. He remembers his visits to where the Colossus machines were housed. “It was an extraordinary spectacle, seeing all those valves lit up and the [paper] tape going round.”

Asked how his Bletchley Park colleagues could build a machine that cracked code generated by a machine they had never seen, Roberts simply declares, “Brilliance, my dear fellow.” The octogenarian adds that it is no exaggeration to call Colossus “the outstanding mental achievement of the 20th century.”

IN PIECES How did this bit of history remain buried for so long? When the war ended, British prime minister Winston Churchill ordered that the Colossus machines be smashed into bits “no bigger than a man’s hand” and that the schematics be destroyed. The machines’ design, function, and operation were classified, and the people who had created them at Bletchley Park were kept from talking about what they had done. Although two Colossus machines survived and were used by British intelligence until the 1960s, for all the world knew they had never existed. So while Eniac’s creators were lauded, the staggering achievements that predated it—the building of Colossus I by Tommy Flowers back in the 1940s, despite the naysayers who doubted it could work, and the mapping of the schematic describing the Lorenz teletype-encryption machine by the 22-year-old William Tutte—remained unsung.

A number of Roberts’s Bletchley Park colleagues died without ever having been recognized for their contributions. But people like Sale have been working to set the record straight. The Cipher Challenge marked the rebuilding of the Colossus machine after a painstaking 14-year effort by a team led by Sale. Finding parts, including all those vacuum tubes, and reconstructing design plans from the recollections of men in their 70s and 80s made for tough sledding. But visitors to the museum in Bletchley Park can now see the computer up close and learn about Great Britain’s cradle of computing. 

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