the general staff building on Saxon Square.
Ciȩżki did not think they were ready yet to attack the Enigma. He gave them instead as their first assignment the solution of a four-letter
Reichsmarine
code—a step up in difficulty from army hand ciphers but a big step away from the Enigma. The three began by making frequency counts of the code groups. Here Rejewski’s actuarial studies found application, since much cryptanalysis rests on statistics. The trio noticed that many codegroups began with Y. Perhaps these groups represented the series of interrogatory words that begin in German (as in English), with
w
, a letter that, like
y
, stands at the end of the alphabet:
wer, was, wann
(who, what, when) and so on. One day, mulling this possibility, they noticed a short, six-group radiogram beginning YOPY that was answered with a four-group message. It appeared to be an exercise in which one operator had put a message into code and transmitted it to another, who had replied. Perhaps the first message was a question, the second its answer—probably, in view of its brevity, a year, with each codegroup representing a digit. The question would then be a query as to when something happened. Was it a battle? The birthdate of a famous man? The three quickly reasoned their way to the supposition that the six-letter message was
Wann wurde Friedrich der Grosse geboren?
(When was Frederick the Great born?) This guess proved correct and yielded as well the meanings of the four reply codegroups: 1, 7, 1, and 2. After making this first break, the three cryptanalysts merely expanded the solution. Their apprenticeship had ended.
The achievements of this young and relatively inexperienced cryptanalytic bureau equaled, curiously enough, those of one of the world’s oldest. France’s military cryptanalysts, whose work dated back decades before World War I, had had a remarkable history of success in cracking German military ciphers during the war. Some of their solutions had aided generals at crucial moments during the fighting. But by 1928 France had reduced the number of her army cryptanalysts to eight, and their capabilities were limited. They did not have the techniques needed to solve rotor machines. They dealt only with simple systems: the German army double transposition that Rejewski and the others had solved in their cryptology class, some German codes, a British code. The cryptanalysts and their superiors seemed content with that. The anti-German revanche that had spurred France to the forefront of cryptology after the defeat of 1871 had evaporated in the victory of 1918; the need for intelligence from code-breaking had declined now that France had shackled Germany with the restrictions of Versailles and possessed an army widely regarded as the best in the world. The attitude was the cryptologic equivalent of the Maginot Line.
But one French cryptologist, at least, was not content with his army’s inadequate results. Gustave Bertrand had enlisted as a private in 1914, was wounded the next year in the Dardanelles, and was assigned after the war to the cipher section of the staff of French forces in Constantinople.
Cryptology attracted him. He served during the 1920s in the cipher sections of various headquarters and in 1929 was summoned to that of the army general staff. The poverty of the codebreakers’ resultsmay have led him to conclude that the coming generation of cipher machines would be solved not by pure cryptanalysis but only with the help of bought or stolen keys or descriptions. He proposed establishing a unit to purchase such information from traitors or to burglarize offices and examine and photograph the needed papers or mechanisms. On October 30, 1930, Bertrand, by now a captain, instituted the new Section D, for
Décryptement et Interceptions
, of the
Service de Renseignements
(Intelligence Service). Section D and the separate cryptanalytic section were both part of the army general staff’s famous Deuxième
Ciȩżki did not think they were ready yet to attack the Enigma. He gave them instead as their first assignment the solution of a four-letter
Reichsmarine
code—a step up in difficulty from army hand ciphers but a big step away from the Enigma. The three began by making frequency counts of the code groups. Here Rejewski’s actuarial studies found application, since much cryptanalysis rests on statistics. The trio noticed that many codegroups began with Y. Perhaps these groups represented the series of interrogatory words that begin in German (as in English), with
w
, a letter that, like
y
, stands at the end of the alphabet:
wer, was, wann
(who, what, when) and so on. One day, mulling this possibility, they noticed a short, six-group radiogram beginning YOPY that was answered with a four-group message. It appeared to be an exercise in which one operator had put a message into code and transmitted it to another, who had replied. Perhaps the first message was a question, the second its answer—probably, in view of its brevity, a year, with each codegroup representing a digit. The question would then be a query as to when something happened. Was it a battle? The birthdate of a famous man? The three quickly reasoned their way to the supposition that the six-letter message was
Wann wurde Friedrich der Grosse geboren?
(When was Frederick the Great born?) This guess proved correct and yielded as well the meanings of the four reply codegroups: 1, 7, 1, and 2. After making this first break, the three cryptanalysts merely expanded the solution. Their apprenticeship had ended.
The achievements of this young and relatively inexperienced cryptanalytic bureau equaled, curiously enough, those of one of the world’s oldest. France’s military cryptanalysts, whose work dated back decades before World War I, had had a remarkable history of success in cracking German military ciphers during the war. Some of their solutions had aided generals at crucial moments during the fighting. But by 1928 France had reduced the number of her army cryptanalysts to eight, and their capabilities were limited. They did not have the techniques needed to solve rotor machines. They dealt only with simple systems: the German army double transposition that Rejewski and the others had solved in their cryptology class, some German codes, a British code. The cryptanalysts and their superiors seemed content with that. The anti-German revanche that had spurred France to the forefront of cryptology after the defeat of 1871 had evaporated in the victory of 1918; the need for intelligence from code-breaking had declined now that France had shackled Germany with the restrictions of Versailles and possessed an army widely regarded as the best in the world. The attitude was the cryptologic equivalent of the Maginot Line.
But one French cryptologist, at least, was not content with his army’s inadequate results. Gustave Bertrand had enlisted as a private in 1914, was wounded the next year in the Dardanelles, and was assigned after the war to the cipher section of the staff of French forces in Constantinople.
Cryptology attracted him. He served during the 1920s in the cipher sections of various headquarters and in 1929 was summoned to that of the army general staff. The poverty of the codebreakers’ resultsmay have led him to conclude that the coming generation of cipher machines would be solved not by pure cryptanalysis but only with the help of bought or stolen keys or descriptions. He proposed establishing a unit to purchase such information from traitors or to burglarize offices and examine and photograph the needed papers or mechanisms. On October 30, 1930, Bertrand, by now a captain, instituted the new Section D, for
Décryptement et Interceptions
, of the
Service de Renseignements
(Intelligence Service). Section D and the separate cryptanalytic section were both part of the army general staff’s famous Deuxième
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