Poland - Bombe

"As he and other German dignitaries laid a wreath at the Tomb of the Unknown Soldier next to the offices of the Biuro Szyfrow [in Poland], Rejewski could stare down at them from his window, content in the knowledge that he could read their most secret communications." - Simon Singh.

Post WWI

The battle to crack the Enigma codes actually began shortly after the first world war. By 1928 Germany had made their Enigma machine more sophisticated such that frequency counts were futile. By 1932, after the Poles attempted to work on a commercial Enigma machine and failed, their cipher bureau, the Biuro Szyfrow, acquired many mathematicians, among them were Marian Rejewski, Jerzy Rozycki and Henryk Zygalski. Up until the Enigma era, it was thought that the best cryptanalysts were linguists but surely and quickly mathematicians took over as the primary role of cryptanalysts, because of the electromechanical nature of Enigma. However, after a good while of work on attempting to understand the wiring of Enigma, the Poles didn't make a solid break through until a German traitor, Hans-Thilo Schmidt opened up.

Traitor

After World War I Schmidt, who was code named "Asche", was rejected by the German Army and miserably failed at his own soap business. Schmidt quickly grew angry with Germany and also became envious of the successes of his brother who, interestingly enough, became head of the signal corps. Shortly after his brother provided him a job, in 1931, Schmidt provided Captain Gustave Bertrand, code named "Rex", of France, documents on Enigma along with some keys but the documents didn't provide information on Enigma's internal wiring, unfortunately. At the end of 1932, Bertrand arranged a working relationship with the Poles in such a fashion that France would continuously funnel information to Poland, while the Poles continued cryptanalysis work. After many months of hard work of deducing patterns from 3 letter encrypted double message keys, Rejewski was able to determine rotor internal wiring and eventually the entire wiring of the Enigma machine. Now, the Poles were able to simulate the Enigma machine.

Cillie

Because the Germans would change the settings of the rotors for each message, the Poles had to next determine how the rotors were consistently being arranged. The Germans sent the initial rotor arrangement as the first 3 letters of the message in the clear. The subsequent 6 letters, made up by the sender, were encrypted and provided the settings for the entire remaining message. Those 6 letters unencrypted, were actually 3 letters written twice to avoid transmission interference. So the receiver would set his rotors to say YSB the initial key of the day and type in the following 6 encrypted letters say HWPCAD which would come out to be say FSJFSJ. The rotor settings would then be changed from YSB to FSJ. So, Polish cryptanalysts would be able to guess particular patterns from particular senders. For instance, one German clerk would almost always use his girlfriend's name "Cillie." After a while the Poles thus called all of the easy guesses "Cillies."

Bomba

However, ultimately, most rotor setting indications were more random. So newer manual techniques were used but as the Wehrmacht grew so did communication and thus these manual operations were not enough. Rejewski then had Wytwornia Radiotechniczna AVA the same radio company that built the simulated Enigmas, develop electromechanical devices called Bomby or Bomba for singular or in English the bombe. The Bomba stood about a meter high and because of the 6 possible rotor settings, 6 Bomba's had to run in parallel. More than likely, the reason why the word bombe was chosen was because of the clicking or ticking noise those machines made while cycling through the possible rotor settings. This allowed the Poles to find solutions in roughly 2 hours. Shortly after, the Germans then made their Enigma machine a little more complex by having their 3 rotors be chosen from a group of 5, for now, instead of a total possible of 6 arrangements now it was 60. So this put a strain on the Bomba because it wasn't designed to handle this extra added complexity.

1939

As an interesting side note, Major Gwido Langer, the Biuro's chief at the time, knew all along each day's key for many months and so it seemed that all of the work by the Polish mathematicians was unnecessary. However, Langer thought that Rejewski would be well trained for the inevitable time that when war began, Langer would not be able to get the codebooks anymore. In 1939 the Poles didn't have enough resources to break the new German Enigma codes. Most importantly, the threat of invasion from Germany was looming and thus during July, Poland finally disclosed their Bombas, Enigma replicas and other pertinent information to English and French cryptanalysts. British officials were utterly amazed at the work the Poles did with the Enigma replicas and the crude ability to break Enigma encrypted messages. This valuable information was disclosed at the nick of time because on September 1, Germany invaded Poland igniting the war on the European continent.