Cipher Bureau (Poland)

• 1. Introduction

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  On the 25th of July 1939, the Polish Cipher Bureau made a gift that would help determine the outcome of World War II. At Pyry, south of Warsaw, Polish officers handed French and British representatives the blueprint for breaking Germany's Enigma machine. Britain and France had been unable to make any headway against Enigma on their own. Five weeks after that meeting, the war began. How did a small Polish intelligence unit crack a problem that had defeated every other allied effort in Europe? And when Poland itself was invaded and occupied, what happened to the people who had carried that secret?

• 2. The Soviet Test

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  Lt. Józef Serafin Stanslicki established Poland's Cipher Section on the 8th of May 1919, as the newly independent state was fighting for survival. The Polish-Soviet War tested this fledgling agency immediately, and it performed in ways that would have seemed impossible on paper. Russian army staffs were transmitting operational orders by radio with almost no encryption discipline. Poland's cryptologists included army Lieutenant Jan Kowalewski and three world-famous mathematics professors: Stefan Mazurkiewicz, Wacław Sierpiński, and Stanisław Leśniewski. Together they broke approximately a hundred Russian ciphers during the war. Colonel Mieczysław Ścieżyński later described the situation plainly. Soviet messages arrived either entirely in plaintext or wrapped in minimal encryption. Trained Polish specialists, he wrote, found decryption "child's play."

  In August 1920, the war's most critical month, Polish cryptologists decrypted 410 signals. Those intercepts included messages from Soviet General Mikhail Tukhachevsky, commander of the northern front. They also included dispatches from Leon Trotsky, the Soviet commissar of war. Each intercept was decrypted the same day or, at the latest, the next day. The results went immediately to the Polish General Staff. Marshal Józef Piłsudski personally read the most important of them. Polish signals work also uncovered a large gap on the Red Army's left flank. Piłsudski drove a war-winning wedge into that gap during the Battle of Warsaw in August 1920, preserving Polish independence. The cryptologists worked under the command of Col. Tadeusz Schaetzel, chief of the General Staff's intelligence section. They operated from Warsaw's radio station WAR, one of only two long-range transmitters Poland had in service. By mid-1931, the various predecessor units were formally merged into a single Cipher Bureau at the Polish General Staff.

• 3. Hunting Enigma

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  In late 1927 or early 1928, a parcel arrived at the Warsaw Customs Office from Germany, declared as radio equipment. A representative of the German firm demanded it be returned before customs officials even opened it. His insistence prompted the officials to alert the Polish Cipher Bureau, whose experts cleared their schedules that Saturday afternoon to examine the contents. Inside the box was not radio equipment but a cipher machine. They studied it, then sealed and returned it. Marian Rejewski, who would later become the Bureau's lead Enigma cryptanalyst, commented that the machine was probably a commercial model. The military version had not yet been developed.

  On the 15th of July 1928, the first German machine-enciphered signals appeared on military radio networks. Polish monitoring stations intercepted them, and the Bureau's German section was instructed to read them. The effort eventually failed and was set aside. In 1929, Major Franciszek Pokorny, then head of the Radio-Intelligence Office, arranged for a secret cryptology course at Poznań University. The instructors included Captain Maksymilian Ciężki and a civilian associate named Antoni Palluth. In September 1932, Captain Ciężki hired three graduates of that course: Marian Rejewski, Jerzy Różycki, and Henryk Zygalski.

  In December 1932, Rejewski achieved what historian David Kahn later described as one of the greatest advances in cryptologic history. He applied the mathematical theory of permutations and groups to the Enigma system. Working through the problem, he determined the precise interconnections of the rotors and reflector. French Military Intelligence Captain Gustave Bertrand had supplied the Bureau with two German documents and two pages of Enigma daily keys. Those materials had come from Hans-Thilo Schmidt, a German who worked at Germany's Cipher Office in Berlin, codenamed Asché by the French. Once Rejewski had reconstructed the machine's logical structure, the Bureau commissioned replicas of the Enigma to be built to his specifications.

• 4. A Moving Target

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  In 1926, the German Navy adopted a modified civilian Enigma as its primary cipher device; the Army followed in 1928. In 1930, a plugboard called the Steckerbrett was added to the machine, dramatically increasing its complexity. It started with just six connecting leads. In February 1936, the Germans shortened the interval for changing rotor order from quarterly to monthly. By October of that year, changes were occurring daily, and the number of plugboard leads climbed to somewhere between five and eight.

  The German Navy, more cautious than the other services, introduced a new indicator procedure in May 1937 that would remain unbroken for several years. In November 1937, the machine's reflector was replaced with a new one, designated Umkehrwalze-B. Rejewski worked out the new reflector's internal wiring. The catalogue of message characteristics then had to be compiled from scratch, using his cyclometer device. In January 1938, Colonel Stefan Mayer ordered a statistical review covering two weeks of Enigma traffic. The Bureau had solved 75 percent of all intercepted messages in that period. Rejewski observed that with slightly more staff, the figure might have reached 90 percent.

  On the 15th of September 1938, the Germans changed the procedure for pre-assigning each day's indicator settings across all Enigma networks. This change undermined the mathematical method the Bureau had relied upon. Henryk Zygalski devised a manual attack using 26 perforated sheets. Marian Rejewski designed a machine called the bomba kryptologiczna, which was built to his specifications. Six sets of Zygalski sheets and six bomby were produced, one for each of the six possible rotor orders.

  On the 15th of December 1938, Germany introduced two additional Enigma rotors. Operators could now choose any three from a set of five, increasing the number of possible rotor orders from 6 to 60. Producing enough new bomby and Zygalski sets to cover all 60 orders was beyond the Bureau's resources. A gap in German discipline provided a way forward. The Sicherheitsdienst, the SS intelligence service, had not adopted the September change and did not do so until the 1st of July 1939. Rejewski used the SD network's old procedure to determine the new rotors' internal wiring. That information made it possible to produce a complete set of Zygalski sheets. Large-scale decryption resumed in January 1940. On the 1st of January 1939, the Germans increased the minimum plugboard connections from five-to-eight to seven-to-ten. When war broke out on the 1st of September 1939, Polish intelligence had established nearly 95 percent of the German order of battle. Much of that work had relied on Enigma decryption.

• 5. Gift at Pyry

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  Lt. Col. Gwido Langer and Major Maksymilian Ciężki led the Polish delegation. They were joined by the three civilian mathematician-cryptologists and by Col. Stefan Mayer, Poland's intelligence chief. France sent Major Gustave Bertrand, the French radio-intelligence and cryptology chief, and Captain Henri Braquenié of the French Air Force. Britain sent Commander Alastair Denniston, head of the Government Code and Cypher School, along with Dilly Knox, the chief British cryptanalyst. Commander Humphrey Sandwith, head of the Royal Navy's intercept stations, completed the British team. Each allied delegation received a Polish-built Enigma replica and the details of Poland's decryption methods. Britain pledged in return to prepare two full sets of Zygalski sheets covering all 60 possible rotor orders.

  Knox's first question at the meeting was about the Enigma's entry drum, specifically how the keyboard letters were wired into it. This wiring had blocked British progress. Rejewski had solved the problem years earlier with the inspired guess that the letters were simply wired in alphabetical order. Knox was described as mortified by how simple the answer was. On the 1st of August 1939, Knox sent the Poles a letter written in Polish. He thanked them "for your cooperation and patience" and enclosed small paper batons and a scarf printed with a Derby horse race. It was an acknowledgment, in gesture, of the cryptological race he had conceded.

  Former Bletchley Park mathematician Gordon Welchman addressed the question of the Polish gift directly. Ultra, he later wrote, "would never have gotten off the ground if we had not learned from the Poles, in the nick of time, the details both of the German military Enigma machine, and of the operating procedures that were in use." Allied Supreme Commander Dwight D. Eisenhower called the intelligence from Bletchley Park "of priceless value to me." He credited it as a "decisive contribution to the Allied war effort." Winston Churchill's gravest fear, even after Germany turned against the Soviet Union, was that submarine wolfpacks would strangle sea-locked Britain. The Battle of the Atlantic turned in part on naval Enigma decryption, which traced its foundations to the work of the Polish Cipher Bureau.

• 6. Exile and Silence

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  On the 5th of September 1939, BS-4 received orders to destroy part of its files and evacuate key personnel. Germany's invasion had made Poland's defeat increasingly clear. After the Soviet invasion of eastern Poland on the 17th of September, the team crossed into Romania. They destroyed their equipment and documentation as they went, then reached France via Yugoslavia and still-neutral Italy. Work resumed at PC Bruno, outside Paris, on the 20th of October 1939. In January 1940, the British cryptanalyst Alan Turing spent several days at PC Bruno conferring with his Polish counterparts. He brought a complete set of Zygalski sheets prepared at Bletchley Park by John Jeffreys. On the 17th of January 1940, the Poles achieved the first break into wartime Enigma traffic: a message dated the 28th of October 1939.

  Until France fell in June 1940, Bletchley Park solved 83 percent of the Enigma keys found. PC Bruno accounted for the remaining 17 percent. Rejewski later commented on this gap. "One can only be surprised," he wrote, "that the Poles had as many as 17 percent of the keys to their credit." After France's capitulation, the Bureau's personnel evacuated to Algeria. On the 1st of October 1940, they resumed work at Cadix, near Uzès in unoccupied Vichy France, under Gustave Bertrand's sponsorship. Over the following two years, Cadix decrypted thousands of Wehrmacht, SS, and Gestapo messages originating from across Europe. The intelligence reached Allied commands and resistance movements alike. On the 8th of November 1942, Bertrand learned from a BBC broadcast that the Allies had landed in French North Africa. He evacuated Cadix the following day. On the 11th of November, German forces entered southern France. On the morning of the 12th, they occupied Cadix itself.

  Jerzy Różycki never made it that far. He and two colleagues, Jan Graliński and Piotr Smoleński, died in January 1942 when the French passenger ship SS Lamoricière sank in the Mediterranean. Marian Rejewski and Henryk Zygalski crossed the Pyrenees with a guide who robbed them at gunpoint. Spanish police arrested both men at the border on the 30th of January 1943. After three months in Spanish custody, the Red Cross secured their release on the 4th of May 1943. They eventually reached Britain and were inducted into the Polish Army as privates. Their assignment was to break German SS and SD hand ciphers at a facility in Boxmoor. Because they had spent time in occupied France, the British considered it too risky to bring them to Bletchley Park.

  Langer and Ciężki were captured by the Germans on the night of the 10th-the 11th of March 1943. Antoni Palluth, who had built much of the Bureau's cryptological equipment, perished in German captivity along with Edward Fokczyński. Despite the pressure each of them faced, none revealed the secret of Enigma decryption. This held true for those captured in France and for AVA workers interrogated in Warsaw under German occupation. Stefan Mayer, the former intelligence chief, later emphasized this fact. In late 1946, Rejewski returned to his family in a devastated Poland, where he lived until February 1980. Zygalski remained in England until August 1978. Neither man worked as a cryptologist again. In 1967, the Polish military historian Władysław Kozaczuk first publicly revealed that Polish mathematicians had broken Enigma before the war. His book, Bitwa o tajemnice, appeared seven years before F. W. Winterbotham's The Ultra Secret brought the wider story to international attention in 1974.