Breaking the Enigma code
Polish contribution to victory

Andrzej Dabrowa, Ph.D.

   

4. Polish Decrypting Effort 1930-1939

Early in the decrypting effort, Polish cryptologists devised a simple method to solve the patch panel interconnect consisting of two paper strips. One strip had six holes representing the six panel interconnect the Germans used initially. This paper strip was overlaid on another paper strip that had Enigma machine rotor encrypting series. When the top overlay and the bottom paper strip aligned with the same letters, this became the solution for the patch panel interconnect. This method worked well for a time until the Germans started changing the number of patch panel interconnects and the method lost its value. When the top overlay and the bottom paper strip aligned with the same letters, this became the solution for the patch panel interconnect. This method worked well for a time until the Germans started changing the number of patch panel interconnects and the method lost its value.

Fortunately, the Polish cryptologists came up with much better method that consisted of an assembly of two Enigma machines, that was able to go quickly through the many combinations generated by the three rotors and patch panel of the Enigma machine. There were six patch panel combinations and 26 (one for each letter of the alphabet) times 26 times 26 rotor combinations, giving a total of 105,456 combinations. In less than 20 minutes they were able to find a solution for the Enigma set up and to decrypt messages.

They called this machine "Cyclometer", i.e. a machine that measured the Enigma machine cycles. In a few years they were able to set up a library of more than 80,000 typical set ups for Enigma. Unfortunately, in November 1937 the Germans changed Enigma again. Within less than a year the Poles were again able to break the code and by mid-1938 they reached the peak of their operation.

Suddenly, in mid-September 1938, a number of German messages could not be decrypted! Polish intelligence agents in Germany found that the Germans were changing the initial rotor positions not once a day but with every message so the existing methods were no longer adequate.

M.Rejewski started working on the problem at once and came up with a new, faster and more powerful approach. It consisted of six Enigma machines connected together and driven by a single motor. They called it "Bomba", a term that was used by the French and later by the British at Bletchley Park. Using "Bomba", all combinations could now be examined in two hours. Since fast decryption was of utmost importance a system consisting of six "Bombas" was designed and production given to AVA, the company previously used. By November 1938 the system was operating and German messages were again being decrypted.

In addition to the "Bomba", H. Zygalski developed a completely new method using perforated paper sheets. Each sheet had 51 by 51 squares and about 1000 holes arranged in a pattern. Twenty-six sheets, one for each rotor position, were required. As the sheets were superimposed and adjusted on each other, holes shone through giving possible solutions. Six sets of these were required for finding possible Enigma settings. This substantially reduced demand on the "Bomba". The advantage of the perforated sheets was that they were not affected by the patch panel setting.

By December 1938 the Germans had introduced new changes which lengthened the encryption sequence and the existing system, though still capable, took a long time to obtain a solution. The Polish team was now reaching the limit of their resources. In July 1939, the Germans added rotors four and five to their machines. This information was gained through Polish intelligence in Germany and cryptologists soon confirmed this by analysis of the new messages. On the basis of new messages and errors committed by German operators, the Polish cryptologists were able to deduce the interconnections in the new rotors. This was possible because for some time the Germans did not use the new encryption methods and consequently some messages were still decryptable although taking about 10 times longer! The only solution was to build a more powerful machine consisting of 60 "Bombas" or 60 sets of perforated sheets. This change of pace, shortage of resources and the imminence of war made the Polish Chief of Staff, Gen. W. Stachewicz, to decide to pass all the information gained by the cryptologists to the French and British.

This had to be done under the greatest security as German spies were everywhere. A conference was set for 25-27 July 1939 to which the French and the British crypto specialists were invited. The conference participants representing France, Britain and Poland were as follows -

From France, Colonel G. Bertrand (radio intelligence) and Captain H. Braquenie (intelligence)

From Britain, Colonel S. Menzies (Chief of British Intelligence), A. Denniston (Chief of G.C.C.S.) and A.D. Knox (cryptologist from G.C.C.S.)

From Poland, Colonel G. Langer (Chief of Cryptology), Major M. Ciezki (Chief of the German section, BS4), M. Rejewski, J. Rozycki and H. Zygalski (cryptologists), A. Palluth (mechanical engineer from AVA) and C. Betlewski (mechanical engineer from AVA).

Col G Bertrand	Gen Sir S Menzies	A Denniston	A D Knox	Capt H Braquenie

To assure the utmost privacy, the conference was held in the Pyry Forest near Warsaw. H. Zygalski presented the Polish made Enigma and explained how it worked. He also explained how they broke the code by mathematical analysis, coupled with information provided by the French intelligence officer Capt. G. Bertrand. The next presentation was by M. Rejewski who demonstrated the six Enigma machines ("Bomba") that they were using to break the code. On the second day it was explained that the Germans were now using Enigmas with five rotors and that, since the decrypting process took ten times longer, the existing system was no longer practical. Further, the Germans had introduced a patch panel with seven to ten interconnects which further complicated the problem. H. Zygalski presented his alternative method, using perforated sheets, but the multiplicity of sheets made it slow and cumbersome.

Col. G. Langer, the Polish Intelligence Section Chief, then addressed the French and British delegations stating that Poland expected to be attacked by the Germans very soon and that the Polish government had decided to pass all the information, drawings, perforated sheets and Enigmas to the Allies. Poland did not have sufficient resources and time to continue with the effort. Within two weeks the French received two Enigmas via diplomatic channels. On August 16th Capt. G. Bertrand, accompanied by Commander W. Dunderdale the British Intelligence Resident in Paris, passed to the British a package containing an Enigma machine and papers relating to breaking the code. Two weeks later, on September 1st, 1939, German forces attacked Poland and started WWII.

Knox's diary and visa		Thank-you note from Knox to the Polish cryptologists

(c) 2003 A R Dabrowa