Man who cracked computer engima

Published on 08/06/2004 12:36

WHEN Alan Turing achieved a distinguished degree at King’s College, Cambridge, in 1934, he appeared to be on course for a successful career as a mildly eccentric don engaged in pure mathematics.

His uniqueness of mind, however, drove him in a direction none could have foreseen.

Turing was fascinated by the concept of creating a mathematical machine to represent thought processes, and it was the "Turing Machine" which became the foundation of the modern theories of computer science.

He also envisaged a "Universal Turing Machine" - one machine for all possible tasks - which embodied the essential principle of the computer.

Turing’s originality lay in seeing the relevance of mathematical logic to a problem originally seen as one of physics. He made a bridge between thought and action, which crossed conventional boundaries.

All this was when he was just 24. Then he left Cambridge for a spell at Princeton and right away saw a link from "useless" logic to practical purposes.

He made a new kind of cipher machine. Although not one of the political intellectuals of the 1930s, Turing followed current events and was influenced by the prospect of war with Germany.

In 1938 Turing returned to Cambridge, and worked part-time for the British cryptanalytic department, the so-called Government Code and Cypher School. His appointment marked the first scientific input into a hitherto arts-based department. That revolution was caused by the failure to penetrate the mechanical Enigma cipher used by Germany.

No significant progress was made, however, until the gift of vital ideas and information in July 1939 from Poland. The Polish success was limited as it depended upon the very particular way the Germans had been using the Enigma.

One of their ideas was embodied in a machine called a Bombe. The way forward lay in Turing’s generalisation of the Polish Bombe into a far more powerful device, capable of breaking any Enigma message, where a small portion of plain text could be guessed correctly. This was achieved within a few weeks after the outbreak of war, after Turing became based at the codebreaking centre, Bletchley Park in Buckinghamshire.

From 1940 onwards, Turing’s Bombe made reading of Luftwaffe signals routine. In contrast, the more complex Enigma methods used in German naval communications were generally regarded as unbreakable. Happy to work alone on a problem that defeated others, Turing cracked the system at the end of 1939, but it required the capture of further material by the Navy, and the development of sophisticated statistical processes, before regular decryption could begin in mid-1941.

TURING’S section then became a key unit at Bletchley Park. By the end of 1941, as the United States entered the war, the battle of the Atlantic was moving towards Allied advantage.

On February 1, 1942, the Atlantic U-boat Enigma machine was given an extra complication and this advantage was suddenly wiped out - nothing could be decoded and catastrophe loomed.

This crisis brought about a new ingredient in Alan Turing’s experience - electronic technology made its first appearance at Bletchley Park as telephone engineers were pressed into an effort to gain ever higher speeds.

Turing crossed the Atlantic in November 1942, for highest-level liaison. Before his return in March 1943, logical weaknesses in the changed U-boat system had been brilliantly detected, and U-boat Enigma decryption was effectively restored for the rest of the war. Turing became an all-purpose consultant to the by now vast Bletchley Park operation. He saw the Fish material - messages enciphered on the quite different system used for Hitler’s strategic communications - cracked by Colossus machines, brought into operation just before D-Day, demonstrating the feasibility of large-scale digital electronic technology.

But he had another and more ambitious end in view. In the last stage of the war he planned the embodiment of the Universal Turing Machine in electronic form or, in effect, the invention of the digital computer.

In 1944, following the invasion of Normandy that Allied control of the Atlantic allowed, Alan Turing was almost uniquely in possession of three key ideas - his own 1936 concept of the universal machine, the potential speed and reliability of electronic technology and the inefficiency in designing different machines for different logical processes. Combined, these ideas provided the principle, the practical means and the motivation for the modern computer.

Turing was captivated by the potential of the computer he had conceived. He held that the computer would offer unlimited scope for practical progress towards embodying intelligence in an artificial form and his design for the Automatic Computing Engine, or ACE, began. Turing’s prospectus for the use of the machine was visionary. But not a single component of the ACE was assembled and Turing found himself without any influence in the engineering of the project.

From October 1947, the National Physical Laboratory allowed, or perhaps preferred, that he should spend the academic year at Cambridge. Out of this came a pioneering paper on what would now be called neural nets.

Meanwhile, the NPL made no advance with the construction of the ACE, and as Turing’s position fell back, other computer projects at Cambridge and Manchester forged ahead.

IN May 1948, Turing was offered the post of deputy director of the computing laboratory at Manchester University. Turing accepted, resigned from the NPL, and moved in October 1948. The meaningless title reflected Turing’s uncertain status. He had no control over the project whose fate was in fact determined by its sudden necessity for the British atomic bomb project.

Though marginalised in practice, he published his theoretical ideas on artificial intelligence in 1950 in a paper which is now one of the most quoted in science. His "Turing Test" for intelligent machinery now has a long and entertaining history. But, always seeking new worlds to conquer, he did not settle for life as a computer guru.

He started on a completely new mathematical theory of the growth and development of living things.

Then in March 1952, Turing was arrested and went on trial after the police learned of his sexual relationship with a young Manchester man. He made no serious denial or defence, telling everyone he saw no wrong with his actions. Rather than go to prison he accepted injections of oestrogen intended to neutralise his libido.

A factor in his life unknown to most around him was he had also continued to work for GCHQ, the post-war successor to Bletchley Park. But since 1948, the conditions of the Cold War and the alliance with the US meant that known homosexuals had become ineligible for security clearance.

No-one could safely have predicted his future course. Turing was found dead by his cleaner on June 8, 1954. He had died of cyanide poisoning, a half-eaten apple beside his bed. His mother believed he had accidentally ingested cyanide from his fingers after a chemistry experiment, but it is more credible he contrived his death to allow her to believe this. The coroner’s verdict was suicide.

In four inadequate words, Alan Turing appears now as the founder of computer science, the originator of a now dominant technology. But these words were not spoken in his lifetime, and he may yet be seen in a different light in the future.

• Andrew Hodges is author of Alan Turing: The Enigma. www.turing.org.uk