Secret Life of Bletchley Park - McKay Sinclair [20]
Right from the start, though, Hugh Foss wasn’t so sure about that. He wrote a paper saying that if enough could be gleaned about Enigma’s internal wiring, then the machine just might be broken with the use of cribs – basically using guessed words or phrases to give a starting point into all the other letters. One crucial key to the machine was that any letter – say, ‘W’ – could never be encrypted as itself. In other words, no matter how often one typed in ‘W’, the letter would never be encrypted as ‘W’. But this didn’t make the task of breaking the machine much easier to contemplate. There were still millions upon millions of potential combinations.
By 1936, when it was increasingly obvious within Whitehall that Hitler’s aggression would not be contained, GC&CS was applying renewed vigour to the Enigma problem. And in 1937, at the time of the Spanish Civil War, Dilly Knox devised a way into the earlier, unmodified version of the machine that was being used by Italy. He did this partly by means of ‘rodding’; Knox’s ‘rods’ were, in the most basic terms, a painstakingly calculated slide-rule style representation of the wiring and rotor position of the machine upon which cipher-text letters could be moved and rearranged.
And the British were not alone in these efforts. There was also invaluable aid from another source, for an early, slightly simpler German military version of the Enigma machine had been cracked as far back as 1932 by several gifted mathematicians in Poland.
The Polish triumph was extinguished a little later in the 1930s when the German army – now regenerated and strengthening, and keen to tighten its security – increased the number of code-letter wheels on the machine from three to five, thus increasing the huge number of potential combinations another tenfold. However, this setback was in part countered thanks to a valiant Frenchman called Major (later Colonel) Gustave Bertrand, who was working in close contact with the Polish mathematicians. ‘I think we should acknowledge what the French did in the field of Enigma,’ says Mavis Batey. ‘And indeed how they really did work with us until the fall of France.’
In the early 1930s, Gustave Bertrand had been carefully monitoring Germany’s development of Enigma and the machine’s uses. Some years earlier he had made contact with a German spy (or traitor, as the Germans themselves would have put it) called Hans Thilo Schmidt. Schmidt supplied Bertrand with crucial Enigma documentation. He had come by such paperwork because he worked in the German Ministry of War.
This was not Bertrand’s only success. ‘When the Germans improved the plugboard of Enigma,’ says Keith Batey, ‘they sent out a manual. And the idiots actually gave a plaintext telling how one set up the machine and this manual gave you the answer. The Germans realised, and recalled the manual right away – but Major Bertrand got hold of one none the less. That’s what gave the Poles the entry they needed.’
The Poles devised two cipher-checking methods. One was a manual method, using ‘Zygalski sheets’, named after their inventor, mathematician Henryk Zygalski. These, in essence, were a series of twenty-six thick sheets, one for each of the Enigma’s possible sequences for the insertion of the machine’s rotors. The sheets had specially prepared grids printed upon them, twenty-six by twenty-six, letters of the alphabet on the outer edges with holes punched or cut through the squares in certain combinations. The principle was based on what were termed ‘females’ – letter positions that would be repeated in an enciphered message. The sheets would be placed on top of one another above an illuminated surface, and moved and rearranged in carefully calculated sequences until the number of lights shining through the holes was reduced to one