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Authors: Hervie Haufler
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produced were made almost unintelligible by scratch-outs and inkblots. When invasion threatened, he melted down a collection of silver coins into ingots, buried them and then, when the crisis had passed and it was time to dig them up, could not remember where they were buried.
In the hunt to unlock the Enigma, though, the Germans never dreamed they would be up against a man of Turing's genius. In those few months between the outbreak of the war and early 1940, he had analyzed the machine, discerned the chinks in its supposedly impenetrable armor and, with Welchman's help, devised the countermeasures that would defeat it.
Months must pass, however, before the redesigned bombes, with all their thousands of soldered connections, would be available. How were the codebreakers to achieve at least partial success in the meantime?
British patience and meticulous attention to detail came to the rescue. GC&CS analysts had been studying the habits of German Enigma operators and had found two subtle mistakes that could be exploited.
The first became known as "Herivel's tip," after John Herivel, a young mathematician recruited by Welchman. Much like Rejewski, Herivel tried to put himself into the shoes of a German code clerk and imagine what the operator might do incorrectly because of laziness or work pressure. Herivel had an insight. At the beginning of each new encoding day, the German operator had a boring series of steps he had to go through. Following instructions, he must choose the correct set of three rotors out of the five available, slide the rotors in proper sequence onto the axle, turn their alphabet rings to the required positions and link up the proper arrangement of the plugboard cables. Then he was supposed to select three random letters for his message key. It was all a big bother. Suppose, Herivel asked himself, the lazy or hurried operator didn't take that final step? Suppose he sent his first message of the day using the same three letters as his rotor ring settings? Herivel suggested collecting the new day's first messages. If there was more than one shortcutting operator, there would be repeatsâand the rotor settings could be surmised.
The second sloppy practice consisted of what BP labeled "cillis." The name may have been derived from the initials of one German clerk's girlfriend, which he used often instead of randomizing his three-letter selections. That was one type of cilliâthe repeated use of familiar sequences, such as HIT and LER. Another form was supplied by German operators who, instead of plucking their three letters out of the air, simply lifted them from their keyboards. A sequence down from the Q key read QAY. One down from PFread WSX. Although these practices were expressly for bidden in the Enigma operators' manuals, lazy or rushed code clerks did resort to them, and from these cillis BP's clever analysts could determine the wheel order for the day as well as the setting for these particular messages. "Unbelievable?" Welchman wrote. "Yet it actually happened, and it went on happening until the bombes came, many months later."
Using these and similar ingenious methods, the BP crew early in 1940 began deciphering the Luftwaffe messages known as Red because that was the color of the pencil Welchman used to demark it from other systems.
By then it had been decided that Welchman and Turing would divide the main Enigma decrypting responsibilities between them. Welchman had moved into Hut 6, one of the wooden structures hastily erected on the park's grounds, and took over its operation when the young John Jeffreys became terminally ill. Welchman's team concerned itself with breaking German air force and army traffic, then passed the decrypts on to Hut 3. There, another team translated them, judged their importance and urgency and determined where they should be disseminated. Turing was responsible for Hut 8, heading up work on the naval Enigma signals, with Hut 4 as his analysis
In the hunt to unlock the Enigma, though, the Germans never dreamed they would be up against a man of Turing's genius. In those few months between the outbreak of the war and early 1940, he had analyzed the machine, discerned the chinks in its supposedly impenetrable armor and, with Welchman's help, devised the countermeasures that would defeat it.
Months must pass, however, before the redesigned bombes, with all their thousands of soldered connections, would be available. How were the codebreakers to achieve at least partial success in the meantime?
British patience and meticulous attention to detail came to the rescue. GC&CS analysts had been studying the habits of German Enigma operators and had found two subtle mistakes that could be exploited.
The first became known as "Herivel's tip," after John Herivel, a young mathematician recruited by Welchman. Much like Rejewski, Herivel tried to put himself into the shoes of a German code clerk and imagine what the operator might do incorrectly because of laziness or work pressure. Herivel had an insight. At the beginning of each new encoding day, the German operator had a boring series of steps he had to go through. Following instructions, he must choose the correct set of three rotors out of the five available, slide the rotors in proper sequence onto the axle, turn their alphabet rings to the required positions and link up the proper arrangement of the plugboard cables. Then he was supposed to select three random letters for his message key. It was all a big bother. Suppose, Herivel asked himself, the lazy or hurried operator didn't take that final step? Suppose he sent his first message of the day using the same three letters as his rotor ring settings? Herivel suggested collecting the new day's first messages. If there was more than one shortcutting operator, there would be repeatsâand the rotor settings could be surmised.
The second sloppy practice consisted of what BP labeled "cillis." The name may have been derived from the initials of one German clerk's girlfriend, which he used often instead of randomizing his three-letter selections. That was one type of cilliâthe repeated use of familiar sequences, such as HIT and LER. Another form was supplied by German operators who, instead of plucking their three letters out of the air, simply lifted them from their keyboards. A sequence down from the Q key read QAY. One down from PFread WSX. Although these practices were expressly for bidden in the Enigma operators' manuals, lazy or rushed code clerks did resort to them, and from these cillis BP's clever analysts could determine the wheel order for the day as well as the setting for these particular messages. "Unbelievable?" Welchman wrote. "Yet it actually happened, and it went on happening until the bombes came, many months later."
Using these and similar ingenious methods, the BP crew early in 1940 began deciphering the Luftwaffe messages known as Red because that was the color of the pencil Welchman used to demark it from other systems.
By then it had been decided that Welchman and Turing would divide the main Enigma decrypting responsibilities between them. Welchman had moved into Hut 6, one of the wooden structures hastily erected on the park's grounds, and took over its operation when the young John Jeffreys became terminally ill. Welchman's team concerned itself with breaking German air force and army traffic, then passed the decrypts on to Hut 3. There, another team translated them, judged their importance and urgency and determined where they should be disseminated. Turing was responsible for Hut 8, heading up work on the naval Enigma signals, with Hut 4 as his analysis
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