Cipher Bureau (Poland)

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The Cipher Bureau (

SIGINT and both cryptography (the use of ciphers and codes) and cryptanalysis
(the study of ciphers and codes, for the purpose of "breaking" them).

The precursor of the agency that would become the Cipher Bureau was created in May 1919, during the

Polish-Soviet War
(1919–1921), and played a vital role in securing Poland's survival and victory in that war.

In mid-1931, the Cipher Bureau was formed by the merger of pre-existing agencies. In December 1932, the Bureau began breaking Germany's Enigma ciphers. Over the next seven years, Polish cryptologists overcame the growing structural and operating complexities of the plugboard-equipped Enigma. The Bureau also broke Soviet cryptography.

Five weeks before the outbreak of

Allies an unprecedented advantage (Ultra) in their ultimately victorious prosecution of World War II
.

Background

On 8 May 1919 Lt.

Polish-Soviet War of 1919–1921, thereby helping preserve Poland's independence, recently regained in the wake of World War I.[2] The Cipher Section's purview included both ciphers and codes.[3] In Polish the term "cipher" (szyfr) loosely refers to both these two principal categories of cryptography.[3] (Compare the opposite practice in English, which loosely refers to both codes and ciphers as "codes".[4]
)

During the

Tsarist army staffs during World War I, to the decisive advantage of their German enemy.[3] As a result, during the Polish-Soviet War the Polish military were regularly kept informed by Russian signals stations about the movements of Russian armies and their intentions and operational orders.[3]

The Soviet staffs, according to Polish Colonel Mieczysław Ścieżyński,

had not the slightest hesitation about sending any and all messages of an operational nature by means of radiotelegraphy; there were periods during the war when, for purposes of operational communications and for purposes of command by higher staffs, no other means of communication whatever were used, messages being transmitted either entirely "in clear" (plaintext) or encrypted by means of such an incredibly uncomplicated system that for our trained specialists reading the messages was child's play. The same held for the chitchat of personnel at radiotelegraphic stations, where discipline was disastrously lax.[6]

General Staff building (Saxon Palace), destroyed in World War II. The arcade still shelters Tomb of the Unknown Soldier, before which stood Thorvaldsen's equestrian statue of Prince Józef Poniatowski. In this building, from 1932, the Cipher Bureau broke the German plugboard military Enigma.

In the crucial month of August 1920 alone, Polish cryptologists

decrypted
410 signals:

etc.[7]

The intercepts were as a rule

Tukhachevsky, including the famous and historic conflict between the two Russian commanders.[9]

The intercepts even included an order from

Trotsky to the revolutionary council of war of the Western Front, confirming Tukhachevsky's operational orders, thus giving them the authority of the supreme chief of the Soviet armed forces.[10] An entire operational order from Tukhachevsky to Budionny was intercepted on 19 August and read on 20 August, stating the tasks of all of Tukhachevsky's armies, of which only the essence had previously been known.[11]

Ścieżyński surmises that the Soviets must likewise have intercepted Polish operational signals; but he doubts that this would have availed them much, since Polish cryptography "stood abreast of modern cryptography" and since only a small number of Polish higher headquarters were equipped with

Polish cryptologists enjoyed generous support under the command of Col.

Polish General Staff's Section II (Intelligence). They worked at Warsaw's radio station WAR, one of two Polish long-range radio transmitters at the time. The Polish cryptologists' work led, among many other things, to the discovery of a large gap on the Red Army's left flank, which enabled Poland's Marshal Józef Piłsudski to drive a war-winning wedge into that gap during the August 1920 Battle of Warsaw.[11]

The discovery of the Cipher Bureau's archives, decades after the

Polish-Soviet War
, has borne out Ścieżyński's assertion

that ... radio intelligence ... furnished [the Polish Commander-in-Chief,

Budionny's Cavalry Army, the Battle of Brody, to the Battles of Warsaw, Lwów and the Niemen.[11]

Cipher Bureau

In mid-1931, at the Polish

General Staff, a Cipher Bureau was formed by merging the Radio-Intelligence Office (Referat Radiowywiadu) and the Polish-Cryptography Office (Referat Szyfrów Własnych).[12] The Bureau was charged with both cryptography – the generation, and supervision of the use, of ciphers and codes – and cryptology – the study of ciphers and codes, particularly for the purpose of breaking them.[13]

Between 1932 and 1936, the Cipher Bureau took on additional responsibilities, including radio communications between military intelligence posts in Poland and abroad, as well as radio counterintelligence – mobile direction-finding and intercept stations for the locating and traffic analysis of spy and fifth column transmitters operating in Poland.[12]

Stalking Enigma

Enigma, an electro-mechanical rotor machine with scrambler comprising entry drum, three rotors, and reflector. This military model also has a plugboard.
Marian Rejewski when he first reconstructed Enigma

In late 1927 or early 1928, there arrived at the Warsaw Customs Office from Germany a package that, according to the accompanying declaration, was supposed to contain radio equipment. The German firm's representative strenuously demanded that the package be returned to Germany even before going through customs, as it had been shipped with other equipment by mistake. His insistent demands alerted the customs officials, who notified the Polish General Staff's Cipher Bureau, which took a keen interest in new developments in radio technology. Since it happened to be a Saturday afternoon, the Bureau's experts had ample time to look into the matter. They carefully opened the box and found that it did not, in fact, contain radio equipment but a cipher machine. They examined the machine minutely, then put it back into the box.[14]

The Bureau's leading Enigma cryptanalyst Marian Rejewski commented that the cipher machine may be surmised to have been a commercial-model Enigma since at that time the military model had not yet been devised. "Hence this trivial episode was of no practical importance, though it does fix the date at which the Cipher Bureau's interest in the Enigma machine began" – manifested, initially, in the entirely legal acquisition of a single commercial-model Enigma.[14]

On 15 July 1928, the first German machine-enciphered messages were broadcast by German military radio stations. Polish monitoring stations began intercepting them, and cryptologists in the Polish Cipher Bureau's German section were instructed to try to read them. The effort was fruitless, however, and was eventually abandoned. There remained very slight evidence of the effort, in the form of a few densely written-over sheets of paper and the commercial-model Enigma machine.

1st Legion Infantry Division, became chief of the Radio-Intelligence Office, and subsequently of the Cipher Bureau.[12] The Bureau's deputy chief, and the chief of its German section (BS-4), was Captain Maksymilian Ciężki
.

In 1929, while the Cipher Bureau's predecessor agency was still headed by Major Franciszek Pokorny (a relative of the outstanding

Poznań University for selected mathematics students. Over ten years later, during World War II while in France, one of the students, Marian Rejewski, would discover that the entire course had been taught from French General Marcel Givièrge's book, Cours de cryptographie (Course of Cryptography), published in 1925.[15]

In September 1932, Maksymilian Ciężki hired three young graduates of the Poznań course to be Bureau staff members: Marian Rejewski, Jerzy Różycki and Henryk Zygalski.[15]

Successes and setbacks

In 1926, the German Navy adopted, as its top cryptographic device, a modified civilian Enigma machine; in 1928 the German Army followed suit.[16] The complexity of the system was much increased in 1930 by the introduction of a plugboard (Steckerbrett), albeit with only six connecting leads in use.[17] In December 1932, Marian Rejewski made what historian David Kahn describes as one of the greatest advances in cryptologic history, by applying pure mathematics – the theory of permutations and groups – to breaking the German armed forces' Enigma machine ciphers.[18][19] Rejewski had worked out the precise interconnections of the Enigma rotors and reflector, after the Bureau had received, from French Military Intelligence Captain Gustave Bertrand, two German documents and two pages of Enigma daily keys (for September and October of that year).[20] These had been obtained by a French military intelligence agent, a German codenamed Rex,[a] from an agent who worked at Germany's Cipher Office in Berlin, Hans-Thilo Schmidt, whom the French codenamed Asché. [b][21]

Cyclometer, devised in the mid-1930s by Rejewski to catalog the cycle structure of Enigma permutations. 1: Rotor lid closed, 2: Rotor lid open, 3: Rheostat, 4: Glowlamps, 5: Switches, 6: Letters.

After Rejewski had worked out the military Enigma's logical structure, the Polish Cipher Bureau commissioned the

doubles") of the Enigma to Rejewski's specifications.[22] His method of decrypting Enigma messages exploited two weaknesses of the German operating procedures.[c] It used what Rejewski called "characteristics" that were independent of the plugboard connections.[23] This involved compiling a card catalog of certain features of the set of indicator settings.[24]

The Germans increased the difficulty of decrypting Enigma messages by decreasing the interval between changes in the order of the rotors from quarterly, initially, to monthly in February 1936, then daily in October of that year, when they also increased the number of plugboard leads from six to a number that varied between five and eight. This made the Biuro's grill method much less easy,[25] as it relied on 'unsteckered' letter pairs.[26] The German navy was more security-conscious than the army and air force, and in May 1937 it introduced a new, much more secure, indicator procedure that remained unbroken for several years.[27]

The next setback occurred in November 1937, when the scrambler's reflector was changed to one with different interconnections (known as Umkehrwalze-B). Rejewski worked out the wiring in the new reflector, but the catalogue of characteristics had to be compiled anew, again using Rejewski's "cyclometer", which had been built to his specifications by the AVA Radio Company.[28]

In January 1938, Colonel Stefan Mayer directed that statistics be compiled for a two-week period, comparing the numbers of Enigma messages solved, to Enigma intercepts. The ratio came to 75 percent. "Nor", Marian Rejewski has commented, "were those 75 percent ... the limit of our possibilities. With slightly augmented personnel, we might have attained about 90 percent ... read. But a certain amount of cipher material ... due to faulty transmission or ... reception, or to various other causes, always remains unread".[29] Information obtained from Enigma decryption seems to have been directed from B.S.-4 principally to the German Office of the General Staff's Section II (Intelligence). There, from fall 1935 to mid-April 1939, it was worked up by Major Jan Leśniak, who in April 1939 would turn the German Office over to another officer and himself form a Situation Office intended for wartime service. He would head the Situation Office to and through the September 1939 Campaign.[30]

A Zygalski perforated sheet (1938)
Diagram of Rejewski's cryptologic bomb. For clarity, only one set of three rotors is shown (1); in reality, there were six such sets. An electric motor (2) turns the rotors. 3: Switches.

The system of pre-defining the indicator setting for the day for all Enigma operators on a given network, on which the method of characteristics depended, was changed on 15 September 1938. The one exception to this was the network used by the Sicherheitsdienst (SD)—the intelligence agency of the SS and the Nazi Party—who did not make the change until 1 July 1939. Operators now chose their own indicator setting. However, the insecure procedure of sending the enciphered message key twice remained in use, and it was quickly exploited. Henryk Zygalski devised a manual method that used 26 perforated sheets, and Marian Rejewski commissioned the AVA company to produce the bomba kryptologiczna (cryptologic bomb).[31]

Both the Zygalski-sheet method and each bomba worked for only a single scrambler rotor order, so six sets of Zygalski sheets and six bomby were produced.[32] However, the Germans introduced two new rotors on 15 December 1938, giving a choice of three out of five to assemble in the machines on a given day.[33] This increased the number of possible rotor orders from 6 to 60. The Biuro could then only read the small minority of messages that used neither of the two new rotors. They did not have the resources to produce 54 more bomby or 54 sets of Zygalski sheets. Fortunately, however, the fact that the SD network was still using the old method of the same indicator setting for all messages, allowed Rejewski to re-use his previous method of working out the wiring within these rotors.[34] This information was essential for the production of a full set Zygalski sheets which allowed resumption of large-scale decryption in January 1940. On 1 January 1939, the Germans made military Enigma even more difficult to break by increasing the number of plugboard connections from between five and eight, to between seven and ten.[26]

When

Polish intelligence, according to Leśniak, "absolutely exceeded what would normally have been possible".[35]

Kabaty Woods

Until 1937 the Cipher Bureau's German section, BS-4, had been housed in the Polish General Staff building – the stately 18th-century "

Pyry, south of Warsaw. There, working conditions were incomparably better than in the cramped quarters at the General Staff building.[36]

The move was dictated as well by requirements of security. Germany's Abwehr was always looking for potential traitors among the military and civilian workers at the General Staff building. Strolling agents, even if lacking access to the Staff building, could observe personnel entering and leaving, and photograph them with concealed miniature cameras. Annual Abwehr intelligence assignments for German agents in Warsaw placed a priority on securing informants at the Polish General Staff.[36]

Gift to allies

It was in the Kabaty Woods, at Pyry, on 25 and 26

cryptanalyst[39] and Commander Humphrey Sandwith, head of the Royal Navy's intercept and direction-finding stations.[40]

When Rejewski had been working on reconstructing the German military Enigma machine in late 1932, he had ultimately solved a crucial element, the wiring of the letters of the alphabet into the entry drum, with the inspired guess that they might be wired in simple alphabetical order. Now, at the trilateral meeting – Rejewski was later to recount – "the first question that ...

Dillwyn Knox asked was: 'What are the connections in the entry drum?'" Knox was mortified to learn how simple the answer was.[41]

The Poles' gift, to their western Allies, of Enigma decryption, five weeks before the outbreak of World War II, came not a moment too soon. Former Bletchley Park mathematician-cryptologist Gordon Welchman later wrote: "Ultra 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."[42] Allied Supreme Commander Dwight D. Eisenhower, at war's end, described intelligence from Bletchley Park as having been "of priceless value to me. It has simplified my task as a commander enormously." Eisenhower expressed his thanks for this "decisive contribution to the Allied war effort".[43]

British prime minister Winston Churchill's greatest wartime fear, even after Hitler had suspended Operation Sea Lion and invaded the Soviet Union, was that the German submarine wolfpacks would succeed in strangling sea-locked Britain.[44] A major factor that averted Britain's defeat in the Battle of the Atlantic was her regained mastery of Naval Enigma decryption; and while the latter benefited crucially from British seizure of German Enigma-equipped naval vessels, the breaking of German naval signals ultimately relied on techniques that had been pioneered by the Polish Cipher Bureau.[45] Had Britain capitulated to Hitler, the United States would have been deprived of an essential forward base for its subsequent involvement in the European and North African theaters.[46]

A week after the Pyry meeting,

Dillwyn Knox, in a letter dated 1 August 1939, thanked the Poles, in Polish, "for your cooperation and patience". He enclosed little paper batons and a scarf picturing a Derby horse race – evidently emblematic of the cryptological race that Knox had hoped to win using the batons, and whose loss he was gallantly acknowledging.[47]

On 5 September 1939, as it became clear that Poland was unlikely to halt the ongoing German invasion, BS-4 received orders to destroy part of its files and evacuate essential personnel.[48]

Bureau abroad

Third Reich
's doom had been sealed years earlier (photo 13, Kozaczuk 1984, after p. 114).

During the German

Enigma doubles and cryptologic equipment for the German section, remained in Poland. Some were interrogated by the Gestapo, but no one gave away the secret of Polish mastery of Enigma decryption.[49]
At

In the interest of security, the Allied cryptological services, before sending their messages over a

Heil Hitler!".[51] As late as December 1939, when Lt. Col. Gwido Langer, accompanied by Captain Braquenié, visited London and Bletchley Park, the British asked that the Polish cryptologists be turned over to them. Langer, however, took the position that the Polish team must remain where the Polish Armed Forces were being formed – on French soil.[52] The mathematicians might actually have reached Britain much earlier – and much more comfortably – than they eventually did; but in September 1939, when they went to the British embassy in Bucharest, Romania, they were brushed off by a preoccupied British diplomat.[53]

In January 1940, the British cryptanalyst

John Jeffreys using Polish-supplied information. On 17 January 1940, the Poles made the first break into wartime Enigma traffic – that from 28 October 1939.[54]

During this period, until the collapse of France in June 1940, ultimately 83 percent of the Enigma keys that were found, were solved at Bletchley Park, the remaining 17 percent at PC Bruno. Rejewski commented:

How could it be otherwise, when there were three of us [Polish cryptologists] and [there were] at least several hundred British cryptologists, since about 10,000 people worked in Bletchley ... Besides, recovery of keys also depended on the amount of intercepted cipher material, and that amount was far greater on the British side than on the French side. Finally, in France (by contrast with the work in Poland) we ourselves not only sought for the daily keys, but after finding the key also read the messages. ... One can only be surprised that the Poles had as many as 17 percent of the keys to their credit.[55][56][e]

German sentries before the Saxon Palace (Polish General Staff building). Photo before 30 August 1940, when the Germans concealed Thorvaldsen's statue of Prince Józef Poniatowski.

The inter-Allied cryptologic collaboration prevented duplication of effort and facilitated discoveries. Before fighting had started in Norway in April 1940, the Polish-French team solved an uncommonly hard three-letter code used by the Germans to communicate with fighter and bomber squadrons and for exchange of meteorological data between aircraft and land.[57] The code had first appeared in December 1939, but the Polish cryptologists had been too preoccupied with Enigma to give the code much attention.[57] With the German assault on the west impending, however, the breaking of the Luftwaffe code took on mounting urgency. The trail of the elusive code (whose system of letters changed every 24 hours) led back to Enigma. The first clue came from the British, who had noticed that the code's letters did not change randomly. If A changed to P, then elsewhere P was replaced by A. The British made no further headway, but the Poles realized that what was manifesting was Enigma's exclusivity principle that they had discovered in 1932. The Germans' carelessness meant that now the Poles, having after midnight solved Enigma's daily setting, could with no further effort also read the Luftwaffe signals.[58][f]

The Germans, just before opening their 10 May 1940 offensive in the west that would trample Belgium, Luxembourg and the Netherlands in order to reach the borders of France, once again changed their procedure for enciphering message keys, rendering the Zygalski sheets "completely useless"[59][60] and temporarily defeating the joint British–Polish cryptologic attacks on Enigma. According to Gustave Bertrand, "It took superhuman day-and-night effort to overcome this new difficulty: on May 20, decryption resumed."[61][g]

Following the capitulation of France in June 1940, the Poles were evacuated to Algeria. On October 1, 1940, they resumed work at Cadix, near Uzès in unoccupied southern Vichy France, under the sponsorship of Gustave Bertrand.[62]

A little over two years later, on 8 November 1942, Bertrand learned from the BBC that the Allies had landed in French North Africa ("Operation Torch"). Knowing that in such an eventuality the Germans planned to occupy Vichy France, on 9 November he evacuated Cadix. Two days later, on 11 November, the Germans indeed marched into southern France. On the morning of 12 November they occupied Cadix.[63]

Over the two years since its establishment in October 1940, Cadix had decrypted thousands of

SS and Gestapo messages, originating not only from French territory but from across Europe, which provided invaluable intelligence to Allied commands and resistance movements.[64][h] Cadix had also decrypted thousands of Soviet messages.[65]

Having departed Cadix, the Polish personnel evaded the occupying Italian security police and German Gestapo and sought to escape France via Spain.[66] Jerzy Różycki, Jan Graliński and Piotr Smoleński had died in the January 1942 sinking, in the Mediterranean Sea, of a French passenger ship, the Lamoricière, in which they had been returning to southern France from a tour of duty in Algeria.[i][67]

SS and SD hand ciphers at a Polish signals facility in Boxmoor. Because of their having been in occupied France, the British considered it too risky to invite them to work at Bletchley Park.[71]

Finally, with the end of the two mathematicians' cryptologic work at the close of World War II, the Cipher Bureau ceased to exist. From nearly its inception in 1931 until war's end in 1945, the Bureau, sometimes incorporated into aggregates under

cryptonyms (PC Bruno and Cadix), had been essentially the same agency, with most of the same core personnel, carrying out much the same tasks; now it was extinguished. Neither Rejewski nor Zygalski would work again as cryptologists.[72] In late 1946 Rejewski returned to his family in a devastated and politically altered Poland, to live there another 33 years until his death in February 1980.[73] Zygalski would remain in England until his death in August 1978.[72]

Secret preserved

Despite their travails, Rejewski and Zygalski had fared better than some of their colleagues. Cadix's Polish military chiefs,

decryption, thus making it possible for the Allies to continue exploiting this vital intelligence resource.[76]

Before the war,

cryptology course, had been co-owner of AVA, which produced equipment for the Cipher Bureau, and knew many details of the decryption technology.[77] In Warsaw, under German occupation, other Cipher Bureau workers were interrogated by German intelligence commissions, and some AVA workers were approached by German agents, but all kept silent about compromises to Enigma.[78]

In popular culture

In 1967 the Polish military historian Władysław Kozaczuk, in his book Bitwa o tajemnice (The Battle for Secrets), first revealed that the German Enigma had been broken by Polish cryptologists before World War II. Kozaczuk's disclosure came seven years before F. W. Winterbotham's The Ultra Secret (1974) changed conventional views of the history of the war.[79]

The 1979 Polish film

decryption.[81]

See also

Notes

  1. ^ Rex had been born Rudolf Stallmann in Berlin in 1871 and had changed his surname to that of his French wife, becoming "Rodolphe Lemoine" [fr]. Kahn 1991, p. 57.
  2. ^ The documents were entitled Gebrauchsanweisung für die Chiffriermaschine Enigma (Instructions for Using the Enigma Cipher Machine) and Schlüsselanleitung für die Chiffriermaschine Enigma (Keying Instructions for the Enigma Cipher Machine).
  3. ^ These were that the indicator setting was defined for the day on the key-setting sheets and that the 3-letter indicator was sent twice as six letters of ciphertext.
  4. Pyry (or Kabaty Woods
    ) meeting took place on only one day, 25 July.
  5. ^ Actually, at this early stage of the war there were nowhere near 10,000 people working at Bletchley Park. Still, there doubtless were a good many more working there than at PC Bruno, outside Paris.
  6. ^ Hugh Sebag-Montefiore, in reliance on Rejewski's unpublished 1967 Memoirs, gives a slightly different interpretation, apparently of the same episode: "The German Air Force was using an uncomplicated code for the weather forecasts it was relaying back to base. The substitutions involved in this code changed every day and the British codebreakers had spotted that they were always the same as the connections for the plugboard sockets on the Air Force Enigma system. So, as soon as the code was broken, the codebreakers knew the plugboard connections for the Air Force Enigma." Sebag-Montefiore (2004) pp. 87, 368.
  7. ^ According to Gwido Langer, the interruption in decryption was shorter, 13–19 May 1940. Kozaczuk 1984, p. 115, note 2.
  8. Knox's method, as well as others that Rejewski no longer remembered." (Kozaczuk 1984
    , p. 117)
  9. Christophe Léon Louis Juchault de Lamoricière, who had been involved in France's conquest of Algeria
    .

References

  1. ^ Bury 2004
  2. ^ Woytak 1988, pp. 497–500
  3. ^ a b c d Ścieżyński 1928
  4. ^ Kahn 1996
  5. ^ Nowik 2004, pp. 25–26
  6. ^ Ścieżyński 1928, pp. 16–17
  7. ^ Ścieżyński 1928, p. 19
  8. ^ Ścieżyński 1928, pp. 19–20
  9. ^ Ścieżyński 1928, p. 25
  10. ^ Ścieżyński 1928, pp. 25–26
  11. ^ a b c d Ścieżyński 1928, p. 26
  12. ^ a b c Kozaczuk 1984, p. 23, note 6
  13. ^ Kozaczuk 1984, p. 212
  14. ^ a b c d Rejewski 1984d, pp. 246–7
  15. ^ a b Rejewski & Woytak 1984b, pp. 230–231
  16. ^ Kozaczuk 1984, p. xiii
  17. ^ Sale, Tony. "Anoraks Corner: a quick revision of the Enigma machine, its physical and operational characteristics". Anoraks Corner. Retrieved 5 June 2011.
  18. ^ Kahn 1996, p. 974
  19. ^ Rejewski & Woytak 1984b, pp. 234–236
  20. ^ Rejewski & Woytak 1984b, p. 256
  21. ^ Kozaczuk 1984, pp. 258–259
  22. ^ Kozaczuk 1984, p. 25
  23. ^ Hodges 1992, p. 170
  24. ^ There were 26 × 26 × 26 = 17,576 possible rotor positions for each of the six rotor orders, giving a total of 105,456 possible indicators.
  25. ^ Calvocoressi 2001, p. 38 citing Rejewski 1984d, p. 263
  26. ^ a b Rejewski 1984c, p. 242
  27. [The Enigma General Procedure] (PDF). Berlin: Supreme Command of the German Navy. Retrieved 26 November 2009 – via Bletchley Park.
  28. ^ Rejewski 1984d, p. 264
  29. ^ Rejewski 1984d, p. 265
  30. ^ Kozaczuk 1984, pp. 58, 64–66
  31. ^ Kozaczuk 1984, pp. 53, 212
  32. ^ Bomby is the plural of bomba.
  33. ^ Herivel 2008, p. 39, citing Rejewski 1984d, p. 269
  34. ^ Herivel 2008, pp. 39–40
  35. ^ Kozaczuk 1984, p. 66
  36. ^ a b Kozaczuk 1984, p. 43
  37. ^ Erskine 2006, p. 59
  38. ^ Herivel 2008, p. 55
  39. ^ Rejewski & Woytak 1984b, p. 236
  40. , vol. 30, no. 4 (2006), pp. 294–305.
  41. ^ Rejewski 1984d, p. 257
  42. ^ Welchman 1982, p. 289
  43. ^ Winterbotham 1975, pp. 16–17
  44. ^ Winston Churchill, Their Finest Hour, pp. 598–600.
  45. ^ Kahn 1991
  46. ^ Christopher Kasparek, review of Michael Alfred Peszke, The Polish Underground Army, the Western Allies, and the Failure of Strategic Unity in World War II, 2005, in The Polish Review, vol. L, no. 2, 2005, p. 240.
  47. ^ Kozaczuk 1984, p. 60
  48. ^ Kozaczuk 1984, p. 70
  49. ^ Kozaczuk 1984, pp. 211–16
  50. ^ Kozaczuk 1984, pp. 69–94, 104–11
  51. ^ Kozaczuk 1984, pp. 70–87
  52. ^ Kozaczuk 1984, pp. 99, 102
  53. ^ Kozaczuk 1984, p. 79
  54. ^ Kozaczuk 1984, pp. 84, 94, note 8
  55. ^ Rejewski (1982) pp. 81–82
  56. ^ Also quoted in Kozaczuk 1984, p. 102
  57. ^ a b Kozaczuk 1984, p. 87
  58. ^ Kozaczuk 1984, pp. 87–88
  59. ^ Rejewski 1984c, p. 243
  60. ^ Rejewski 1984d, pp. 269–70
  61. ^ Bertrand (1973) pp. 88–89
  62. ^ Kozaczuk 1984, pp. 112–118
  63. ^ Kozaczuk 1984, p. 139
  64. ^ Kozaczuk 1984, pp. 139–40
  65. ^ Kozaczuk 1984, p. 116
  66. ^ Kozaczuk 1984, pp. 148–151
  67. ^ Kozaczuk 1984, p. 128
  68. ^ Kozaczuk 1984, pp. 150–51
  69. ^ Kozaczuk 1984, p. 154
  70. ^ Kozaczuk 1984, pp. 205–207
  71. ^ Kozaczuk 1984, pp. 148–155, 205–9
  72. ^ a b Kozaczuk 1984, p. 224
  73. ^ Kozaczuk 1984, pp. 224–26
  74. ^ Kozaczuk 1984, pp. 156, 220, note 4
  75. ^ Kozaczuk 1984, p. 156
  76. ^ Kozaczuk 1984, p. 220
  77. ^ Kozaczuk 1984, pp. 26, 212
  78. ^ Kozaczuk 1984, pp. 212–216
  79. ^ Kozaczuk 1984, p. xi
  80. ^ "Sekret Enigmy". IMDb. September 1979.
  81. ^ Peter, Laurence (20 July 2009). "How Poles cracked Nazi Enigma secret". BBC News.

Bibliography

External links