Cipher Department of the High Command of the Wehrmacht

The Cipher Department of the High Command of the Wehrmacht (German: Amtsgruppe Wehrmachtnachrichtenverbindungen, Abteilung Chiffrierwesen) (also Oberkommando der Wehrmacht Chiffrierabteilung or Chiffrierabteilung of the High Command of the Wehrmacht or Chiffrierabteilung of the OKW or OKW/Chi or Chi) was the Signal Intelligence Agency of the Supreme Command of the Armed Forces of the German Armed Forces before and during World War II. OKW/Chi dealt with the cryptanalysis and deciphering of enemy and neutral states' message traffic and security control of its own key processes and machinery, such as the rotor cipher machine ENIGMA machine. It was the successor to the former Chi bureau (German: Chiffrierstelle) of the Reichswehr Ministry.[1]

Short name

The letter "Chi" for the Chiffrierabteilung is, contrary to what one might expect, not the Greek letter Chi, nor anything to do with the chi test,[2] a common cryptographic test used as part of deciphering of enciphered message, and invented by Solomon Kullback, but only to the first three letters of the word Chiffrierabteilung (English:cipher department).

German cryptology service structure during World War II

From the early 1930s to the start of the war, Germany (Weimar Republic), has a good understanding, and indeed a lead in both cryptoanalytic and cryptographic cryptology services. The various agencies had cracked the French–English inter-allied cipher, the Germans with some help from the Italian Communications Intelligence Organization stole American diplomatic codes, and codes taken from the British embassy in Rome, that enabled the breaking of the cipher,[3][4] leading to some gains early in the war. Although the Germans worked to ensure its cryptologic services were effective at the outbreak of the war, the service offerings fragmented considerably among the German armed forces. OKW/Chi had jurisdiction over the entire military cryptologic bureaus, chairing the executive committee, for a number of reasons including increased specialisms for specific military tasks against opposing forces of a similar type, the inherent independence of agencies, and agencies vying for power and favour from Hitler, it was inevitable that the three military branches of German forces operated independently.[3]

In total eight organizations operated within the forces, each operating on its own terms, even though OKW/Chi was considered the premier organization controlling both cipher creation and decipherment of enemy crypts.[3] These eight bureaus which practiced cryptology were split between military and civilian control:[5]

Military

Civilian

Although OKW/Chi continually pushed for the integration of all five military services, it was last blocked in Autumn 1943 by Ribbentrop, Göring, and Himmler.[6] It wasn't until November 9, 1944, that OKW/Chi was formally made responsible for control of for all signals intelligence activities across all forces, by the order of Hitler.[6]

Background

The OKW/Chi was one of the highest military agencies of the Wehrmacht, but with a dual focus: on cryptography, creating Germany's own secure communication systems, and the monitoring of enemy broadcasts and news analysis. As far as cryptanalysis was concerned, OKW/Chi tended to act as troubleshooter, providing the highest service to the Wehrmacht, instead of setting policy as its power to set military SIGINT was limited.[7]

The unit began as the cipher section of the German Defense Ministry in the 1920s. The Cipher Bureau followed later in the 1930s. They were more interested in diplomatic communications than foreign military communications, which were in short supply, and viewed the diplomatic communications as a way to train staff during peacetime.[7] With the rise of the Nazis, the unit grew from 10 people in 1937 to almost 200 people by the outbreak of World War II. By the end of the war, it had almost 800 individuals working there, and its focus had changed to strategy.[7]

It was true that a certain amount of development and security work was always done. The original charter was obscure, but since the Army, Navy and the Air Force was each responsible for its own security development, the only defining commitment of OKW/Chi was to develop ciphers for the agents of the Abwehr. The separate branches were free to submit their own systems to OKW for security scrutiny. This was changed in Oct 1942, ensuring that no new ciphers could be introduced by the Armed Forces unless they were first checked by the OKW. OKW/Chi made some efforts to set up an additional section in section IV, but this work was buried within the organization with OKW/Chi remaining an organization that produced military intelligence.[7]

Contrast this with Bletchley Park, the UK Government Code and Cypher School during World War II, the direct opposite (the enemy) of OKW/Chi, which had almost 12,000 personnel working at the end of the war and had a singular focus on cryptanalysis services and an integrated strategy across all the services from the start of the war.

OKW/Chi was one of the primary targets of TICOM, the operation by the United States to seize military assets after the war.[7] This article consists in part of material from those reports (See: Notes).

Key personnel

The most important individual at OKW/Chi was Chief Cryptologist Director Wilhelm Fenner, who was the Head of Main Group B, including Group IV Analytical cryptanalysis working with Specialist Dr. Erich Hüttenhain.[8] A German by birth, Wilhelm Fenner went to high school in St Petersburg.[7] His father was an editor of a German language newspaper. He moved back to Germany in 1909 to study Berlin Royal Institute of Technology but was drafted into the Army when World War started, eventually joining the Tenth Army, serving as an intelligence officer.[7] After the war, Fenner met Professor Peter Novopaschenny, a former Tsarist cryptanalyst who taught Fenner the Black Arts of Cryptography, and who went on to become Chief of the Russian subsection on OKW/Chi.[9] They both joined the Cipher Bureau in autumn 1922 initially working in temporary positions. The following year, Fenner was made chief of the Bureau.[7] He worked there until just after the war, discharged on 19 June, eventually working as a car and cycle mechanic in Straubing.[7]

Chief Cryptanalyst Specialist Dr. Erich Hüttenhain was a mathematician hired in 1937 to create a specialized cryptanalytic research unit to investigate enemy cryptologic systems and to test Germany's own cryptologic systems and processes. Together with Dr. Walter Fricke, also a mathematician of some distinction, and his assistant, he was also moved to England to be interrogated by TICOM after the war.[7]

Colonel Hugo Kettler was an administrator who had commanded OKW/Chi since the summer of 1943. His intimate knowledge of the working of OKW/Chi, enabled him to provide information to TICOM, that the OKW/Chi archive papers had been moved to Schliersee.[7]

Lieutenant Colonel Metting was a signals officer who worked up to command the Germany Armies cryptoplogic centre, Inspectorate 7/VI from November 1941 to June 1943. After working in the Signals Battalion on the Eastern Front for several months, He was assigned second in command of OKW/Chi in December 1943.[7] After the war he was considered such a high-value target that he was moved to England to be interrogated by TICOM.

Organization

The following information was prepared by TICOM agents, by comparing the interrogation documents of Colonel Hugo Kettler, Director Wilhelm Fenner, Dr. Walter Fricke and Dr. Erich Hüttenhain. TICOM believed that the information was correct.[10]

1939 to summer 1944

OKW/Chi passed from peace to war without change to its organization. Preparations had been made in 1938 to define staff numbers but at outbreak, personnel were increased by about 30%. In 1939, OKW/Chi was called The Cryptologic Bureau (German:Chiffrier-stelle) and was a part of the Inspectorate of the Signal Troops.[11] At the start of the war The Cryptologic Bureau was commanded by Oberstlt (Colonel) Fritz Boetzel as Director of Operations with his deputy being Major Andrea. He was replaced by Colonel Hugo Kettler during summer of 1943. Boetzel and Andrea were both executed in Summer 1944 when it was suspected that Colonel Boetzel was part of the Lucy spy ring.

The organization of OKW/Chi was broken down into 4 groups which were named Group I to Group IV.

In 1938, OKW/Chi had no mechanical aids to use for the quick decryption of enemy messages once the cipher was broken. Although major attempts were made to mechanize the process, it was realized only in late 1943 that additional specialist personnel would be needed, and they were not available.

OKW/Chi was primarily an intelligence gathering organization at this point, with its only commitment to develop ciphers for Military Intelligence (Abwehr) Each branch of the armed forces were free to submit their system for testing, but were under no obligation to do so. In October 1943, OKW/Chi gained control for cipher development across all military agencies by an order of Field Marshall Keitel, Chief of Staff of the Supreme Command Armed Forces (OKW).[11][12]

Summer 1944 to March 1945

The organization and mission of OKW/Chi changed significantly in the summer of 1944, principally centered on the attempted assassination of Hitler.[11] Whereas OKW/Chi has supposed jurisdiction over all cipher agencies within the Armed Forces, after Summer 1944, OKW/Chi no longer acted like a service agency, but instead set policy and became the primary jurisdiction for all work done on cipher development, message decryption and associated machinery design and construction.[11] The organization changed significantly, with new commanding officers, more focus for Chi IV function and increased staffing levels.[11]

OKW/Chi classified the manner of how they would work with other agencies. How they were classified depended on whether a particular agency had influential Nazi party members in their leadership. The Army had close ties with OKW/Chi but other classifications, for example, the Kriegsmarine and Luftwaffe proved more difficult to control and were never subordinate to OKW.[11][13] Agreement was needed to ensure common process, control and cipher machinery. The Waffen-SS was considered a third classification. OKW had no control over it and special orders had to be issued to enable liaison to start.[11]

OKW/Chi was organized into four principle groups heading by Colonel Kettler, with his deputy Major Mettig.[11] These were the personnel section, Main Group A, Main Group B and Group X. Group A contained Section I, Section II and Section III. Group B contained Section a, Section b and Section c. Group A assignment was the development of their own cryptographic systems and the interception of foreign radios and cables. Group B assignment was cryptanalysis of foreign government communications, the development of mechanical cryptanalysis devices including training in such devices. Group X assignment was the scanning and forwarding of deciphered telegrams to suitable offices including the keeping of a day book recording the most important data.

  • Section Ia: It had control of signal intelligence cover for inter-state communications and control of fixed intercept stations and their branch stations. It contained 2 staff.
  • Section Ib: Study of communications systems of foreign countries and consisted of 2 staff.
  • Section Ic: Responsible for both the Abwehr and OKW/Chi's own telecommunications equipment, including deployment and upkeep. It contained 2 officers and 24 staff.
  • Section IIa: Section IIa's activities varied, and included the following. Camouflage systems for use in German telephonic and radio communications. Passing of requests to monitoring services. Preparation of code and cypher manuals and working instructions. Ownership of key allocation policy. Security scrutiny. Investigation of loss and compromise. Captain Bernsdorf was in control of IIa and had some 6 staff.
  • Section IIb: Developed German code and cypher systems (camouflage, codes and cyphers and telephone secrecy) and also advised on the production of keys and the supervision of production. Specialist Dr Fricke was in control of IIb and had some 14 staff.
  • Section IIc: Controlled by Inspector Fritz Menzer with a staff of 25. Codes and cyphers for agents. Fritz Menzer was considered an Cryptographic Inventor Extraordinaire by cryptographic historian David P Mowry.[14]
  • Section IVa: Managed by Dr Stein with a staff of 11. Its duties were the testing of accepted and new cypher procedures and devices (camouflage, codes and cyphers, and telephone security). The sections purpose was to determine the degree of security of devices and processes. It also tested newly invented devices.
  • Section IVb: Managed by Wilhelm Rotscheidt with a staff of 28. Its duties was the development and construction of decoding devices and the deployment of decoding devices. This was specifically for the decoding offices of Chi and various departments of the Armed Forces and several Government departments.
  • Section IVc: Managed by Prof Dr Franz, it had a staff of 48. Its duties were the scientific decoding of enemy crypts, the development of code breaking methods and working on re-cyphering systems not solved by practical decoding.
  • Section IVd: Managed by Dr Hüttenhain, he provided training and instructions. Conducted lectures and prepared tutorial materials.
  • Section VIa: It conducted wireless interception and managed the sound recording machinery. It was also in charge of listening station Ludwigsfelde, provided analytical solutions to foreign re-encipherments, was in charge of communication between intercept stations and controlled the wireless equipment. It consisted of some 60 individuals.[10]
  • Section VIb: It managed radio news services and photographic image transmission. It consisted of some 60 individuals.[10]
  • Section VIc: It intercepted and monitored non-German radio broadcast services. It consisted of some 30 personnel.[10]
  • Section VId: This section evaluated radio broadcasts and press news. It published the chi-bulletins, and created normal and special reports according to subject. It consisted of 12 personnel.[10]
  • Section VIIa: It kept the day book, and also evaluated and distributed VN-bulletins as necessary.
  • Section VIIb: It organized and indexed messages into categories including family name, place names and subjects such as politics. It also distributed the information on cards as necessary.

Disintegration

By end of 1944 and the beginning of 1945, Chi had begun to disintegrate.[15] Increasing bombing and difficult working conditions in Berlin forced Chi to transfer to Army Signal School in Halle on 13 February 1945.[15] Message decryption continued on a limited scale. On 13 April 1945, Chi partially dissolved when Colonel Hugo Kettler dismissed all staff who wanted to go home. All remaining personnel of Chi again moved on 14 April by military train to Werfen in Austria. It ceased to exist the next day. All papers and machinery was destroyed in anticipation of the American forces, the American Ninth Army arriving in the next few days.[15]

Operations

Linguistic output

The final output from Chi IVb, i.e. from the linguists, was the translation of decoded traffic into a product called Reliable Reports (German:Verlässliche Nachrichten), and were classified as Top Secret (German: Geheime Kommandosache).[13] Missing words or garbled messages were replaced by dots. Doubtful translations were enclosed by parentheses with a question mark. Article Reliable Reports contains an example VN.[13]

The principle recipient of the most important VNs was General Alfred Jodl, Chief of Operations and Hitler, with a copies being sent to other agencies and archives and used for additional processing, for example cribbing.[13] That material which was considered of no importance was discarded. The linguistic section produced an average of 3000 VNs per month.[13]

TICOM seized most of the VNs and which represent the traffic of 29 countries and are now available at the US National Archives for viewing.[16] A Combined British and American team combed the VNs for Intelligence after the war and it was known that Churchill read a number.[13]

Day to day operations

Friction in day-to-day activities occurred between Fenner and other personnel and military agencies, and was not considered satisfactory from an efficiency standpoint. Neither the head of Abwehr, nor indeed head of OKW/Chi really understood the difficulties involved in cryptanalysis, nor the operational resources required for a specific task.[13] A directive was issued to Fenner to break a particular American strip system by a particular Sunday. This was completed, purely by chance and hard work, and met the deadline. As Dr Hüttenhain stated:

From that point on, personnel were continually concerned that specific ciphers were to be broken to order.

OKW/Chi managed to keep up a continuous stream of VNs even when conditions started to become intolerable, primarily due to the continual bombing. OKW/Chi had been bombed out of its regular headquarters in the Tirpltzufer section in Berlin by November 1943, close the Abwehr headquarters.[13] From that point it was moved to temporary buildings which were unheated and sometimes without doors and windows.[13] During the last 3 years of the war, a continual thinning of the ranks, reduced active personal in Main Group B down to about 321 from a peak in 1941.[13]

Interception

OKW/Chi ran two distinct interception networks, which included legacy systems from previous agencies.[13] One system concentrated on diplomatic messages sent in Morse code and most messages were encrypted and received from enemy and neutral states. Messages picked up on this system were sent to OKW/Chi for decipherment. The second network's mission was to monitor foreign news broadcasts, with all traffic sent in clear text, and included such news agencies as Reuters, and Domei.[13] The second system was also used to testing of new or special equipment.

The first network and by far the largest consisted on three large intercept stations at Lauf and one at Treuenbrietzen.[13] and one at Lörrach.

The Treuenbrietzen station was created in 1933 and used to pick up diplomatic traffic before the war. It was subordinated by OKW/Chi in 1939,[13] but little is known about it since staff escaped to Werfen at the end of the war and they were never interrogated by TICOM.[13]

The Lauf station started life intercepting diplomatic traffic in 1933, but was also subordinated by OKW/Chi in 1939 and expanded considerable. It has three small intercept stations on its own.[13] These were stations at Lörrach with 8 intercept sets to track Swiss traffic, Tennenlohe was a backup/emergency station with 5 sets and there was a small station at Libourne in France, operating 9 sets from 1943 and used to track Swedish and Turkish Traffic.[13]

Lauf had between 200-250 people running it, including outstations with over 80 women after January 1944. It used around 90 receiving sets. TICOM primary witness to the running of Lauf was Specialist Flicke,[17][18] who stated:

[Lauf's primary] mission was to intercept all diplomatic traffic including the traffic from the Polish underground.

Dr Wilhelm F. Flicke would later write a book at the request of the German Military in the 1950s of his experiences at Lauf. The book was called War Secrets in the Ether[19] (which was restricted (English translation) by the NSA, and Britain, until the early 1970s).

The Lauf station was intercepting 25000 messages per day by late 1942,[13] but this changed when closer control was instigated in early 1943 to only focus on specific messages groups, dropping the message count down to about 10000 per day.[13]

The intercept network ran special stations called Out Stations, described by Colonel Mettig as being directly subordinated to Group I at OKW/Chi instead of Lauf and deemed to be fairly small and often in foreign countries.[13] They were administered by the Abwehr. Two were known to exist, one in Spain and one in Sofia. The Sofia outstations had considerable difficulty in contact OKW/Chi often using shortwave radio.[13]

The Spain outstation employed around 50 men, around 1941. Communication between this outstation and OKW/Chi was by wireless and courier. One outstation was first located in the German consulate in Madrid, later in 1942 it moved to night club and later to the edge of the city in 1942 to avoid conflicting radio signals.[13] Other outstations existed, one in a cattle ranch in Seville others in Tangiers and on the Canary Islands.

The outstations conducted work with the official approval of the host country, e.g. in Spain. Extreme and elaborate security precautions were continually in operation to keep he network secret. Outstation personnel were forbidden to mix with the locals, ordered to travel in small group, married men couldn't contact their wives and single men were forbidden to marry Spanish women.[13] Certainly it was known that certain men conducted clandestine meetings with Spanish women who were known to be in the high positions in both the Spanish government and military.[13]

Other outstations existed in Rome, Belgrade, Vienna, Budapest, Bordeaux, also in Greece.[13]

The interception system control loop was controlled by Group I of OKW/Chi. Colonel Mettig would prepare a monthly report in conjunction with Chief Cryptologist Wilhelm Fenner, of the most interesting links (that a listening station had made) as he appreciated them, based on this knowledge. This was sent to Section IV who examined the links, made decisions as to what to listen for, and this was fed back to the intercept station in question via the Abwehr.[13] The control loop was continually refined to ensure that language desks who were solving specific traffic received new intercepts specific to that desk.[13]

OKW/Chi would also receive traffic from other military agencies. These included the Reichspost, OKW/Fu and the Forschungsamt (Research bureau)Hermann Göring's personnel cipher bureau.[13]

Around 500 people worked on the Lauf interception network when outstations were included.

Little is known about the second intercept system, which had its main station at Ludwigsfelde with branch stations at Koenigsberg, Gleiwitz, Muenster and Husum.[13] What is known is that Ludwigsfelde station was very well equipped with 80 receiving sets. It was completely destroyed by an air attack on 2 January 1944[13] and was not back in operation until the Autumn 1944. Colonel Kettler stated under TICOM interrogation that it kept up a monthly average of 7,280 press reports and 7340 phone transmissions during the period from January to June 1944.[13]

The bulk of interception was either ordinary Morse code or radio telephone, with little attempt to expand into other traffic types, e.g. Baudot[13]

Training

Training was a regular occurrence at OKW. Occasionally training would be provided in elementary cryptology for those personnel who were considered neither a strategic ally, nor an ally who wasn't directly involved with Wehrmacht operations. Sometimes advanced courses would be undertaken, for particular groups within Wehrmacht. However, most of the training was for OKW personnel.[13] When Dr Hüttenhain started in 1937, he was trained for six months and practiced on low grade Spanish government military systems. Generally when a new member joined, who could speak a foreign language they started as linguists and were gradually introduced into cryptology, working for 2 days per week in the six winter months.[13] Later, advanced courses for more able candidates were undertaken, but the candidates were expected to undertake significant research work and work on new problems almost immediately after completion. In November 1944, the courses were dropped.[13]

Defensive cryptology

Defensive cryptology in this context enables secure communication between two individuals, in the presence of a third party. During World War II, defensive cryptology was synonymous with encryption, i.e. the conversion of information from a readable state to apparent nonsense. The originator of an encrypted message shared the decoding technique needed to recover the original information only with intended recipients, thereby precluding unwanted people from doing the same. German Armed Forces relied on a series of devices and processes to accomplish this task.

German high-level cryptologic systems were insecure for a number of reason, although they were considered brilliantly conceived by TICOM agents.[20] Large outlays of both personnel and resources by the Allies cost Germany dear, from 1942 onwards. For example, Admiral Doenitz stated at his Nuremberg trial:[20]

The Battle of the Atlantic was nearly won prior to July 1942; when German losses were within reasonable limits. But they jumped 300 per cent when Allied aircraft, aided by radar; which came like an epileptic stroke, were used in the fight." He reported 640 to 670 submarines and 30,000 men lost as a result of British and American action.

The OKW/Chi cipher department report blamed Radar on new aircraft. It was never realized, even to the end of the war and the trials, that cryptanalysts of the Government Code and Cypher School at Bletchley Park had broken the Air Force (Luftwaffe) Enigma and read all Air Force communications from 1942 onwards.[20][21]

The chief German cryptological machine for defense, was the Enigma machine.[13] It seemed inconceivable that OKW/Chi and the German armed forces failed to understand how insecure the system was.[20] The Wehrmacht had a generally uneasy feeling regarding Enigma and their own key processes and missed a number of opportunities to definitively prove this. These were:

One Allied PW in North Africa had said the United States and British operated with a very large joint 'park' of IBM (Hollerith) machinery, but this interrogation was never followed up. No personalities whatever were known.

German military cryptographers failed to realize that their Enigma, T52 and other systems were insecure.[20] Although many attempts were made to try and validate the security of the Enigma, which the whole of the Wehrmacht cryptographic infrastructure regarding secure communication, rested on, they failed. The reason for this, was they were unable to conduct sufficiently deep security tests to determine how secure they were.[20] They were also unable to put forth the costly practical effort required to solve them. Their security tests were theoretical only, and they were unable to imagine what a large concerted effort at traffic analysis could achieve.[20] A security measure which would have proved productive, was the issue of new Enigma rotors. However, so many Enigma machines were out in the field, that it would prove impractical to update them.[20] OKW/Chi also felt that even if a particular Enigma unit was captured, it would still be considered secure, since no process was known by OKW/Chi that could break it. They also had not advanced sufficiently in cryptology to realize what could be achieved by a large combined engineering team. The Allies had undertaken that effort and had been reward with huge successes[20] Also Germany was unable to cryptanalyze British and American high-grade systems (Ultra) carrying critical Allied data. As a result, OKW/Chi had no hint that their own high-grade systems were insecure.[20]

Curiously, a number of systems were under development at OKW/Chi and at other agencies which would have been considered secure. The introduction of the pluggable reflector (German: Umkehrwalze D) called Uncle Dick at Bletchley Park. It was introduced in Spring 1945 and made obsolete the Bombe.[20] This necessitated, the development of the new updated Bombe, called the Duenna. Dr. Huettenhain said in TICOM interrogation:[20]

The [Air Force] had introduced the pluggable reflector, but the Army said it was too much trouble.

A number of other possibly secure systems were developed including Fritz Menzer’s cipher device 39 (SG-39) (German: Schlüsselgerät 39).[20] Although invented in 1939, it was designed to replace the Enigma machine, but delays over its design ensured it was never rolled out. Only 3 devices were built.[23] The cycle for an unmodified ENIGMA is 16,900. When configured according to Menzer’s instructions, the SG-39 had a cycle length of 2.7 × 108 characters—more than 15,000 times as long as the Enigma.[24]

Although it was unknown whether these new systems would have made OKW/Chi processes and devices secure, it would probably have complicated the allied cryptanalytic effort.[25]

Mechanical aids

Development of OKW/Chi cipher machines rested with the Ordnance office.[13] Although OKW/Chi remit was to analyze a number of devices to find their perceived weaknesses, they never constructed any themselves.

The chief German cryptological machine was the Enigma machine.[13] It was invented by the German engineer Arthur Scherbius at the end of World War I, was regarded as antiquated and was considered secure only when used properly, which was generally not the case later in the war.[13] Director Fenner was instrumental in getting them introduced into use.[13] One item alone, the variable-notch rotor (German: Lückenfüllerwalze) would have made the Enigma secure after 1942.

The Siemens and Halske T52-E (German:Geheimschreiber) i.e. the G-Schreiber was considered a secure teleprinter.[13] It was considered modern but not mobile enough. By the end of 1944 planned developments were halted with no further practical work undertaken.[13]

Safety testing the cipher machines

Enigma

In October 1942, after starting work at OKW/Chi, the mathematician Gisbert Hasenjaeger was trained in cryptology by Dr. Hüttenhain. Hasenjaeger was put into a newly formed department, whose principal responsibility was the defensive testing and security control of their own methods and devices.[26] Hasenjaeger was ordered, by the mathematician Karl Stein who was also conscripted at OKW/Chi, to examine the Enigma machine for cryptologic weaknesses, while Stein was to examine the Siemens and Halske T52 and the Lorenz SZ-42.[26] The Enigma machine that Hasenjaeger examined was a variation that worked with 3 rotors and had no plug board. Germany sold this version to neutral countries to accrue foreign exchange. Hasenjaeger was presented with a 100 character encrypted message for analysis and found a weakness which enabled the identification of the correct wiring rotors and also the appropriate rotor positions, to decrypt the messages. Further success eluded him however. He crucially failed to identify the primary and most important weakness of the Enigma machine, the (lack of fixed points due to the reflector), was missed. Hasenjaeger could take some comfort from the fact. Even Alan Turing missed the weakness. Instead, the prize was left to Gordon Welchman, who used the knowledge to decrypt several hundred thousand Enigma messages during the war.[26]

Siemens & Halske T-43

The Siemens & Halske T43 T-43 (German:Schlüssel-Fernschreibmaschine) was a cipher teleprinter, which used a one-time key tape to supply a sequence of keying characters instead of mechanical rotor wheels as in other T-series models.[20] The teleprinter was developed in 1943 and introduced in 1944.[27] A serious defect was discovered in the T-43 by Section IVa head Dr Stein in early 1944, but this was corrected. The defect enabled the reading of T-43 messages. Later when TICOM found the device, it was tested and found that the key tape was only pseudo-random. This meant that the T-43 was insecure.[20]

Siemens and Halske T-52

The T52 secure teleprinter, was tested on an ongoing basis over the war period. Versions T-52A and T52-B were tested by Dr. Hüttenhain in 1939 and found in his words: to be extraordinarily insecure. Versions A and B was already in production.[13] T-52C was tested by Dr Doering, Mathematician stationed at Inspectorate 7/VI, in 1942 was found to be insecure and could be broken using a text of 1000 letters.[13] T-52D was also tested by Doering with help from OKW/Chi decipherment machinery and found to be insecure. Both Versions C and D were still being produced even though they were known to be insecure. OKW/Chi had no control over production, with difficulties presented by Army high command accepting their faults.[13] Version T52-E was tested by Dr. Hüttenhain using the new decryption machinery and found to be also insecure.[13] By the end of 1944, production had ceased.

Lorenz SZ-40

The original Lorenz SZ-40 began development in 1937 by the Army Ordanance Development and Testing Group Signal Branch, in conjunction with C. Lorenz AG. Originally no help from OKW/Chi was requested, but in late 1937, Dr. Hüttenhain, Senior Inspector Menzer of OKW/Chi and Dr. Werner Liebknecht, a cryptologic tester from C. Lorenz AG, tested the first SZ-40 and found it could be broken with 1000 letters of text without cribs.[13] Only 100 of these were produced. Model SZ-42 was produced and found to be insecure. Versions A, B and C were designed in conjunction with Dr Hüttenhain and his assistant Dr Karl Stein. It is unknown if versions B and C were tested, however it was found that version A was also tested and found to be insecure.[13]

Offensive cryptology

Given some encrypted messages ("ciphertext"), the goal of the offensive cryptologist in this context, is for the cryptanalyst to gain as much information as possible about the original, unencrypted data ("plaintext") through whatever means possible.

Insufficient cooperation in the development of one’s own procedures, faulty production and distribution of key documents, incomplete keying procedures, overlooked possibilities for compromises during the introduction of keying procedures, and many other causes can provide the unauthorized decryptor with opportunities.[28]
Dr. Erich Hüttenhain 1978

Rapid analytic machinery

Although OKW/Chi were ahead in the use of mechanical aids before the war, these were mostly electro-mechanical devices, and little use was found for newer valve or electronic based devices. In fact the use of electro mechanical cryptanalytic devices fell during the war.[29] Although some work was done to prototype working models, in general it was mostly experimental work. Experiments did show one thing, that paper tape was far too slow, and that the future was photo-electric scanning of text.[29]

OKW/Chi developed a series of teleprinter tape devices, to examine the periodicity or repetition of text, which employed early design of a photo-electric readers. They employed paper tapes, rather than celluloid film, which was used by the allies.[20] By the end of the war, the first German film device was in construction. TICOM reported that it was similar to the USA developed Tetragraph-Tester[30] (Tetragraph). It had speed of around 10k letters per second, against the USA development device at 500k letters per second.[20]

Interrogation of Dr Hüttenhain of OKW/Chi IVa by TICOM revealed:

By 1941, it had become clear that machines would be necessary for the dual - offensive and defensive - task of research, but engineers were not obtained until Autumn 1942 when the following were appointed: Two graduate engineers, Willi Jensen and Wilhelm Rotscheidt.[31] both telecom experts; three working engineers, TODT, Schaeffer and Krachel and 25 mechanics.[20]
They decided to use IBM Hollerith machines wherever possible, but it was found that this machinery was not suitable for all problems. The machines which resulted were built in a more generalized way than the immediate problem demanded so that they could be used again.[20]

The following machines were built.

Digraph weight recorder

The digraph, i.e. Bigrams weight recorder (German: Bigramm Suchgereat) was a search apparatus for making frequency evaluations of digraphs and recording the results. It was used to find expected sequences of Bigrams, which with a certain probability attached, indicated a possible weak point in a cryptographic system. It was built at a cost of ℛℳ6400 Reichsmarks, $5800 at 1945 conversion rate, and was the most expensive machine owned by OKW/Chi.[20]

It was used to break the Japanese two-letter code (J-19) and would find a solution in less that 2 hours.[20] According to Dr Hüttenhain:

The machine was once used to work on an English meteorology cipher... used by the Air Force Weather Service

The device made the solutions of a single transposition (Transposition cipher) easy. A message being study must be broken into likely columns, with these matched against each other, with the resulting bigrams (Digraphs) examined for their suitability.[20]

It consisted of a two teleprinter reading head, a relay-bank interpreter circuit, a plugboard weight assigner and a recording pen and drum. Each head read the tape using a photo-electric reader at a speed to 75 characters per second. The interpreter took the two readings and translating then from two separate letters reading into one digraphic reading, which it sent to the plugboard.[20]

The plugboard contained 676 relays on its left side, corresponding to the number of Bigrams available in the Latin alphabet.[3] These could be wired at will to any jack in any one of the five different sets of relays on the right hand side of the plugboard; these sets representing weights, i.e. each bigram could be assigned a weight from 1 to 5. For example, (D->5), (I->3),(O->1),(P->1). In this manner, the digraph DE was given the weigh 5, the digraph IL the weight 3, the digraph PC and OX the wight 1. All other bigrams had a weight 0.[20]

The recording device was paper drum pen recorder, with the recording consisting of a cylindrical spiral, with undulations being recorded, whose heights varying with the weights assigned to the digraph.[20] Two tapes with the message to be decrypted, were looped, with one tape being one or more character longer, so they would slide relative to each other. The result would be Kappa plot indicating, bigram by bigram, for every possible juxtaposition of the whole message against itself,

Analysis of the results would show visually (by dense undulations of the plot), along its length, the probability of a good match at each point along its length, became apparent.[20]

It could also be used to discover coincidences (‘parallels’), which would be used to find interrupted repetitions.[3]

Polygraphic coincidence counter

The Polygraphic coincidence counter (Frequency analysis) (German:Saegebock, English:Sawbuck) was a machine for recording the frequency of polygraphs occurring in a message,[3] or for recording the frequency of polygraphic coincidences between messages. It was particularly useful for periodic substitutions. Polygraph sizes includes decagraphs. It cost of ℛℳ1580 Reichsmarks, $1200 at 1945 conversion rate.[20]

The apparatus consisted of two teleprinters with paper tape photo-electric reading heads, a calculator (not described by TICOM) and ten different recorders. Each reader had a reading speed of 75 characters per second.[20] Each recorder used a pen which made a dash on a paper strip 30 cm wide, wherever a signal was read from the calculator. During the first read of the full loop, each recorder would make a small vertical stroke every time a coincidence occurred. Thus, if there were 10 digraphic coincidences during the first full looping, the recorder number 2 made 10 small strokes, each above the other and so on. Another device, the trigram recording device output was chained to the bigram, and in a manner up to the Hasgram (10-gram) device. The devices automatically gave a Kappa plot for single characters, bigrams, etc. Although a hundred times faster that doing the method manually, working at 50 characters a second scanning speed, for a text of 600 characters took two hours.[3][20][31]

Dr Hüttenhain and Walther Fricke his assistant did not identify the types of cryptographic systems this device was constructed for.[3] Dr Hüttenhain did state however:

The problem was to determine the periods in short periodic substitution by finding the distance between repeats in a message...It (the counter) could also find two Enigma machine messages in depth.

These types of machines were considered a class of Phase and Periodic Frequency Searching machines (German: Phase neuchgereat) also (German:Perioden-und-Phasensuchgerat) .[31]

Statistical Depth Increaser

The statistical depth increaser (German:Turmuhr, English:Tower clock) was a machine for testing sequences of 30 letters statistically against a given depth of similar sequences, to determine whether message belonged to a given depth. (Substitution cipher)[20]

It was used to decrypt the US Strip cipher when cribbing (Substitution cipher) was impossible. It cost of ℛℳ1100 Reichsmarks, $1015 at 1945 conversion rate.[20]

The apparatus consisted of a single paper tape read with a standard teleprinter head, at a speed of 1.5 symbols per second. To paraphase TICOM - A storage device, by which any one of five different scores could be assigned, on a basis of frequency, to each of the letters in the 30 separate monoalphabets that resulted from the 30 columns of depth; a distributor that rotated in synchronization with the tape stepping, and selected which set of 30 scores were to be used as basis for evaluating the successive cipher letters. A pen recording device was used.[3][20]

Enciphered sections of encrypted test on the same generatrix (A curve that, when rotated about an axis, produces a solid figure), were superimposed properly. As a result, the letters within columns fell into successive and separate mono alphabets with characteristic frequencies. A new section of 30 letters of cipher text would have to "match" these alphabets, i.e., show a greater than random number of coincidences with them, before it could be added to this depth. The machine was used to test the probability of such a match. Weights were assigned each letter in each of the basic thirty alphabets, depending on the frequencies therein, and these weights were "stored" in the machine.[3][20] Paper tape was read in sequences of 30 characters in succession. A long resultant stroke by the recording pen meant a greater total weight, therefore a long resultant stroke probably belonged to the basis set of superimposed sequences.[20]

Dr Hüttenhain and Fricke stated:

The cipher text passages already recognized as the same key are stored in the calculating apparatus (not described to TICOM) of the tower clock as a basis on which to start. In such a way that each of the different substitution alphabets receive different scores according to the frequency of the cipher texts...[20]

The machine was called Tower Clock because it ticked at every set of calculations.[20]

Differencing calculator (non recording)

The Differencing[32] calculator was a manually operated device which was designed to assist additive recovery in super-enciphered cipher coded messages, by speeding the differencing[32] of depth of super-enciphered (codegroups) and the trail of likely additives therein.[20] The machine cost of ℛℳ46 Reichsmarks, $40.00 at 1945 conversion rates. It was identical to the US Navy CXDG-CNN-10ADW, code name "Fruit"[32] often called the NCR differencing calculator.

The German version had a capacity of thirty 5-figure code groups, as against the NCR capacity of 20. The German device was much slower to operate, though far simpler in operation.[20]

This device could be operated by the cryptanalyst at their own desk.[20]

Differencing calculator (recording)

The differencing calculator with recording (German:Differenzen Rechengereat, English:Differencing Calculating Apparatus) was a machine designed to compute a flag of difference[32] for a set of enciphered code groups and record it. it consisted of two teleprinter tapes with photoelectric reading heads, a set of calculating relays and an recording electric teleprinter. The read heads operated at 7 characters a second, bounded by the speed of the teleprinter where time was lost by the carriage return and line feed. It cost ℛℳ920 Reichsmarks, $800.00 at 1945 conversion rates.[20]

The figure groups between which differences were to be made were on punched tape. A duplicate of the tape was made, with one blank group added with the two tapes looped and read at the same time. The calculating relays computed the difference (modulo 10) between the two groups and the teleprinter recorded it; the two tapes then stepped simultaneously and the difference between the second and third was computed and recorded; then between the third and fourth; and so on. On the second time around, since the duplicate tape was one group longer than the or1ginal, the offset was automatically changed so that the first group was now differenced[32] with the third group, the second with the fourth, and so on. In this way every group was differenced with all other groups.[20]

Likely additive selector

The likely additive selector (German:Witzkiste:English:Brainbox") was a simple device for removing additives from a column of super-enciphered codegroups arranged in depth. It could be used with any four-digit encrypted code, whose frequency of decrypted code groups had been discovered from previous removal of additives.[20] Five-digit codes used the differencing[32] calculator. The cost of the device was unknown, but estimates put its price at less than ℛℳ57.5 Reichsmarks, $50.00 at 1945 conversion rates.

Simple counting apparatus

Dr Hüttenhain described it as follows:

By means of a simple counting apparatus, it is possible to quickly work our statistics, when there are more than 100 different elements.
100 counting machines, (which were general post office machines), were put side by side. The text for which statistics are to be worked out in punched on tape. The perforated strip is read and a symbol in each case put in the corresponding counter. The counters are read off and their position photo recorded.
In practice this apparatus was used with success within the scope of the investigations into the security of our own system

The devices cost was approximately ℛℳ57.5 Reichsmarks, $600.00 at 1945 conversion rates.[20]

Proposed repeat finder

The proposed repeat finder (name not recorded by TICOM) was one of the first ultra high speed machines, planned and in production but not finished. It was designed to study from 20 to 25 letters for repetitions of 5 of more characters. Each message could be 500 letters in length, with the study of 10k letter of the message at any one time. Dr Hüttenhain states as follows:

The 10,000 letters were recorded one after another as 5-unit alphabetical symbols onto an ordinary film. A duplicate was made. Both strips were now to pass at high speed in front of a photocell reader. In the event the two strips being completely identical for at least 5 letters, this passage would be likewise registered without inertia [photocell].
The strips were to pass before the reading device at a speed of 10000 symbols per second. Accordingly, not quite three hours would have been required to [Work through 10000 letters] i.e. (10,000 x 10000 =100,000,000 comparisons.).

The US rapid analytic machine was most nearly like the German device was the Tetragraph Tester[30] by the Eastman Kodak Company for OP-20-G and the Army Security Agency.[20] When Alan Turing arrived at OP-20-G on 20th Nov. 1942, he was show a run of the machine at that time. No report of the meeting was kept, but a report surfaced on 23 Jan 1943, RAM-2, [Indicating this was the second version, 2 of 3], that prior to January 8, the device was working in an unreliable fashion. During testing, it was missing as much as 60% of hits which were known to exist which had been previously analyzed by hand.[30] Although the Americans eventually perfected the machines, OKW/Chi found the device to be too sensitive for continuous use and with the very limited availability of materials and personnel, it was never completed.[20]

Achievements

According to the TICOM interrogations during 1945, the following information about OKW/Chi successes was recorded and a table prepared which was recorded in Table 2-1 in Vol 1 Synopsis.[33]

When Colonel Mettig was asked point blank what was the greatest achievement of OKW/Chi, he hesitated. It became apparent that OKW/Chi had not achieved any outstanding cryptanalytic successes.[34] However, OKW/Chi did have a number of successes, but generally its cryptologic successes were in what was considered by TICOM to be low and medium grade or medium security cipher systems.[35]

OKW/Chi's cryptanalysis was not outstandingly successful against systems of high security. This may have been not only because the Allies high security systems were actually high security, but in some part unsolvable to the Allies cryptanalysts as well, but because the OKW/Chi cryptanalysts never became technically proficient enough to undertake the solution to these high-security systems.[35]

TICOM agents considered OKW/Chi's greatest achievements were, the fast design and construction of Rapid Analytic Machinery, which were often built quickly under war conditions, e.g. bombing, and where lack of materials was an ever consistent and increasing concern and the continual productions of VN's, (Reliable Reports), up to 3000 per month, even when the war was almost over in January, February 1945, which was a remarkable achievement.

Further developments

However, in the last few decades, a number of military historians have continued the examination of military documentation in relation to World War II and a number of facts have emerged which seem to contradict the TICOM findings, which were highlighted by the Christos Website.[36]

According to the TICOM reports in Volume 1, Table 2.1, the Japanese Purple [cipher] had not been read by the Germans, although it was attacked by AA/Pers Z. No mention was made of attacks by OKW/Chi or other German Axis agencies.[37]

In TICOM Vol 2, it states, "Although they were successful with the Japanese "Red" machine, they did not solve its successor, the "purple" machine."[35]

The solving of the Japanese Purple, considered unbreakable by the Japanese, would indicate the OKW/Chi and the other German agencies were capable of solving high-level security systems. Certainly the Germans knew by 1941 (Purple Cipher - Weaknesses and cryptanalysis), that the purple cipher was insecure, although it is unknown whether OKW/Chi learned this.

The evidence for this revolves around Cort Rave. Professor Dr Cort Rave had started working at OKW/Chi in 1941 and worked as a translator in the Japanese desk of Section IVb and had been detached in December 1943 to the Foreign Office cryptanalytic Section (AA/Pers Z) for training in the Chinese and Japanese Desks.[38] He is listed as an OKW/Chi employee by TICOM,[39] but was considered a minor light by TICOM with an inconsistent memory.[13] However, Rave took the time to conduct personnel communication between the German naval historian Jürgen Rohwer and mathematician Prof. Dr. Otto Leiberich, while in advanced old age, as part of a fact finding process conducted by Rohwer, regarding German cryptological successes during World War II.

Rohwer is a naval historian who has written over 400 books and essays.[40]

Dr. Otto Leiberich worked in OKW/Chi, but would work in the new German Chiffrierstelle from 1953, and from 1973, was the boss of Dr. Erich Hüttenhain, who was Director of the Central office of Encryption (ZfCh) between 1956 and 1973 and who was the boss of Leiberich. Leiberich became founder of Federal Office for Security in Information Technology (BSI) in 1990.[41]

The contents of Dr Rave's letter, dated 01.03.96, were published in Dr Rohwer's book Stalin's Ocean-going Fleet: Soviet Naval Strategy and Shipbuilding Programs with the letter reference on page 143.[42]

Rave stated that:

...the Purple (cipher) has been broken by the Foreign Office and OKW/Chi....

A further piece of evidence was offered by author Dr Wilhelm F. Flicke, who is also described as an employee of OKW/Chi working in the intercept network at Lauf [18][43] and whose book, War Secrets in the Ether[19] (which was restricted (English translation) by the NSA, and Britain, until the early 1970s) described how many messages between Japanese military attache and later Japanese ambassador Hiroshi Ōshima to Nazi Germany, in Berlin, were intercepted at Lauf and deciphered by OKW/Chi.[44]

The mathematician Otto Leiberich believed that the Purple cipher had been broken and considered certain individuals of OKW/Chi to have sufficient capability, insight and technical knowledge to break the cipher, even within certain constraints and the TICOM documentation seems to support it (TICOM I-25). However, no absolute proof exists to prove it.

German mathematicians who worked at OKW

From an examination of Friedrich L. Bauer book, Decrypted Secrets. Methods and Maxims of cryptography and the TICOM documentations, the following German mathematicians worked in or in conjunction with OKW:

Notes

TICOM documentation archive consists of 11 primary documents Volume I to Volume IX. These primary volumes, are aggregate summary documentation, each volume targeting a specific German military agency. The archive also consists of Team Reports, DF-Series, I-Series, IF-Series and M-series reports which cover various aspects of TICOM interrogation.

Volume III which covers OKW/Chi contains over 160 references to the I-Series TICOM documents which are TICOM Intelligence reports, and covers references to the full gamut of the other types of reports, e.g. DF-Series, IF-Series, of which there are over 1500 reports.

See also

References

  1. ↑ Friedrich L. Bauer: Decrypted Secrets. Methods and Maxims of cryptography. 3d revised and expanded edition. 2000, p. 412
  2. ↑ David Kahn (5 December 1996). The Codebreakers: The Comprehensive History of Secret Communication from Ancient Times to the Internet. Simon and Schuster. p. 574. ISBN 978-1-4391-0355-5.
  3. 1 2 3 4 5 6 7 8 9 10 R. A. Ratcliff: Delusions of Intelligence: Enigma, Ultra, and the End of Secure Ciphers. Oct 2006, p 36
  4. ↑ John Ferris: Intelligence and Strategy: Selected Essays. Routledge; New edition 25 June 2005, Page 337 Note 80 - RG 457/145 Major Gamba - An Account of the recovery of the keys of the Inter-allied Cipher; Admiral Maugeri - Italian Communications Intelligence Organization.
  5. ↑ R. A. Ratcliff: Delusions of Intelligence: Enigma, Ultra, and the End of Secure Ciphers. Oct 2006, p. 38-40
  6. 1 2 Friedrich L. Bauer: Decrypted Secrets. Methods and Maxims of cryptography. 3 revised and expanded edition. 2000, p 32
  7. 1 2 3 4 5 6 7 8 9 10 11 12 "OKW/Chi (High Command)". sites.google.com. Ticom Archive. Retrieved 7 January 2014.
  8. ↑ Friedrich L. Bauer: Decrypted Secrets. Methods and Maxims of cryptography. 3 revised and expanded edition. 2000, p 447
  9. ↑ Friedrich L. Bauer: Decrypted Secrets. Methods and Maxims of cryptography. 3 revised and expanded edition. 2000, p 472
  10. 1 2 3 4 5 6 7 8 9 10 11 12 http://www.ticomarchive.com/the-archive, TICOM archive:I-Series, Document:I-39 OKW-Chi.pdf, Organisation of OKW/Chi
  11. 1 2 3 4 5 6 7 8 9 10 "DF-187A Fenner OKW Crypro service.pdf" (PDF). European Command Intelligence Center. Retrieved 1 Feb 2014.
  12. ↑ "European Axis Signal Intelligence in World War II Volume 1" (PDF). NSA. Retrieved 12 July 2014.
  13. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 "European Axis Signals Intelligence World War 2 Volume 3" (PDF). http://www.nsa.gov. Retrieved 31 Jan 2014. External link in |publisher= (help)
  14. ↑ David P. Mowry, “Regierunges-Oberinspektor Fritz Menzer: Cryptographic Inventor Extraordinaire,” Cryptologic Quarterly, Vol. 2, Nos. 3-4, Fall/Winter 1983-84, 21-36.
  15. 1 2 3 "The Career of Willian Fenner" (PDF). European Command Intelligence Center. Retrieved 7 May 2014.
  16. ↑ Hitler, the Allies, and the Jews By Shlomo Aronson, November 2004, Cambridge University Press Page 199
  17. ↑ "European Axis Signals Intelligence World War 2 Volume 3" (PDF). http://www.nsa.gov. p. 38. Retrieved 28 July 2014. External link in |publisher= (help)
  18. 1 2 http://www.ticomarchive.com/the-archive, TICOM archive:I-Series, Document:I-44 Memorandum on speech encipherment by ORR Huettenhain and SDF Dr Fricke
  19. 1 2 Wilhelm F. Flicke (1 April 1994). War Secrets in the Ether. Aegean Park Press. ISBN 978-0-89412-233-0.
  20. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 "European Axis Signal Intelligence in World War II Volume 2" (PDF). NSA. Retrieved 18 June 2014.
  21. ↑ Adamy, Dave (July 2003). "Bletchley Park". Journal of Electronic Defense Page 16
  22. ↑ Meyer, Joseph A. Der Fall WICHER: German Knowledge of Polish Success on ENIGMA (PDF). NSA. p. 27. Retrieved 10 February 2015.
  23. ↑ David P. Mowry: German Cipher Machines of World War II Center for Cryptologic History, National Security Agency, Revised edition 2014, p18
  24. ↑ David P. Mowry: German Cipher Machines of World War II Center for Cryptologic History, National Security Agency, Revised edition 2014, p28
  25. ↑ David P. Mowry: German Cipher Machines of World War II Center for Cryptologic History, National Security Agency, Revised edition 2014, p22
  26. 1 2 3 Cooper, S. Barry; Leeuwen, J. van (3 June 2013). Alan Turing: His Work and Impact: His Work and Impact. Elsevier Science. p. 936. ISBN 978-0123869807. Retrieved 15 March 2014.
  27. ↑ "Siemens T-43". www.cryptomuseum.com. Crypto Museum. 7 May 2013. Retrieved 12 July 2013.
  28. ↑ Friedrich L. Bauer: Decrypted Secrets. Methods and Maxims of cryptography. 3 revised and expanded edition. 2000, p 470
  29. 1 2 "DF-187 Fenner.pdf" (PDF). European Command Intelligence Center. Retrieved 18 May 2014.
  30. 1 2 3 Teuscher, Christof (29 Mar 2005). Alan Turing: Life and Legacy of a Great Thinker. Springer; 1st ed. 2003. 2nd printing 2005 edition (29 Mar 2005). p. 464. ISBN 3540200207. Retrieved 23 June 2014.
  31. 1 2 3 Friedrich L. Bauer: Decrypted Secrets. Methods and Maxims of cryptography. 3 revised and expanded edition. 2000, Section 17.3.2 Page 335
  32. 1 2 3 4 5 6 Christensen, Chris. "US Navy Mathematicians Vs JN-25" (PPTX). Northern Kentucky University. Retrieved 23 June 2014.
  33. ↑ "Volume 1 -- Synopsis, Table 2-1" (PDF). NSA. p. 54. Retrieved 28 July 2014.
  34. ↑ "Volume 3--The Signal Intelligence Agency of the Supreme Command, Armed Forces" (PDF). NSA. p. 55. Retrieved 20 July 2014.
  35. 1 2 3 "Volume 2 -- Notes on German High Level Cryptography and Cryptoanalysis" (PDF). NSA. p. 86. Retrieved 20 July 2014.
  36. ↑ Christos, T. (9 September 2011). "German success with Purple ?". Christos Military and Intelligence Corner. Christos Military and Intelligence Website. Retrieved 27 July 2014.
  37. ↑ "Volume 1 -- Synopsis, Table 2-1" (PDF). NSA. p. 54. Retrieved 20 July 2014.
  38. ↑ http://www.ticomarchive.com/the-archive, TICOM archive:I-Series, Document:I-55 Interrogation of German Cryptographers of the PerZs' Department of the Auswartiges Section 51,52
  39. ↑ "European Axis Signals Intelligence World War 2 Volume 3" (PDF). http://www.nsa.gov. p. 122. Retrieved 27 July 2014. External link in |publisher= (help)
  40. ↑ http://www.wlb-stuttgart.de/seekrieg/rohwer.htm
  41. ↑ Leiberich Vom Diplomatischen Code zur Falltürfunktion - 100 Jahre Kryptographie in Deutschland, Spektrum der Wissenschaft, Juni 1999 und Spektrum Dossier Kryptographie, 2001
  42. ↑ Mikhail Monakov; Jurgen Rohwer (12 November 2012). Stalin's Ocean-going Fleet: Soviet Naval Strategy and Shipbuilding Programs, 1935-53. Routledge. pp. 1905–1906. ISBN 978-1-136-32198-6.
  43. ↑ "European Axis Signals Intelligence World War 2 Volume 3" (PDF). http://www.nsa.gov. p. 112. Retrieved 27 July 2014. External link in |publisher= (help)
  44. ↑ Friedrich L. Bauer: Decrypted Secrets. Methods and Maxims of cryptography. 3 revised and expanded edition. 2000, p 415

Further reading

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