Compromise of Soviet codes in WWII

Signals intelligence and codebreaking played an important role in WWII. British and American codebreakers solved many important Axis crypto systems, such as the German Enigma machine and the Japanese Navy’s code JN25. 

Historians have not only acknowledged these Allied successes but they’ve probably exaggerated their importance in the actual campaigns of the war.

Unfortunately the work of the Axis codebreakers hasn’t received similar attention. As I’ve mentioned in my piece Acknowledging failures of crypto security all the participants suffered setbacks from weak/compromised codes and they all had some successes with enemy systems. 

Britain, the Soviet Union and the United States did not have impenetrable codes. In the course of WWII all three suffered setbacks from their compromised communications.

After having dealt with the United States and Britain it’s time to have a look at the Soviet Union and their worst failures. 

Move along comrade, nothing to see here

Compromises of communications security are usually difficult to acknowledge by the countries that suffer them. For example since the 1970’s countless books have been written about the successes of Bletchley Park, yet detailed information on the German solution of Allied codes only started to become available in the 2000’s when TICOM reports and other relevant documents were released to the public archives by the US and UK authorities.

In Russia the compromise of their codes during WWII has not yet been officially acknowledged and the archives of the codebreaking organizations have remained closed to researchers. This is a continuation of the Soviet policy of secrecy.

The Soviet Union was a secretive society and information was tightly controlled by the ruling elite. This means that history books avoided topics that embarrassed the regime and instead presented the officially sanctioned version of history. Soviet era histories of WWII avoided references to codes and ciphers and instead talked about ‘radio-electronic combat’ which dealt with direction finding, traffic analysis and jamming (1).

After the fall of the Soviet Union several important government archives were opened to researchers and this information has been incorporated in new books and studies of WWII. However similar advances haven’t taken place in the fields of signals intelligence and cryptologic history. Unlike the US and UK that have admitted at least some of their communications security failures the official line in Russia is that high level Soviet codes were unbreakable and only unimportant tactical codes could be read by the Germans. Even new books and studies on cryptology repeat these statements (2).

However various sources such as the TICOM reports, the war diary of the German Army’s signal intelligence agency Inspectorate 7/VI and the monthly reports of the cryptanalytic centre in the East Horchleitstelle Ost clearly show that the Germans could solve even high level Soviet military and NKVD codes.

Overview of Soviet cryptosystems

The secretive Soviet state used various cryptosystems in order to secure its communications from outsiders. The task of preparing and evaluating cipher procedures was handled by two main Soviet organizations, the NKVD’s 5^th Department and the Army’s 8^th department of the main intelligence directorate GRU.

In the 1920’s simple substitution systems were used and these were solved by codebreakers in Poland (Polish-Soviet war of 1919-21) and in Britain (ARCOS case). In the 1930’s the communications of units in the Far East were read by the Japanese codebreakers  and during the Soviet-Finnish war of 1939-40 Soviet codes were read by the Finns with disastrous consequences for the Soviet armed forces.

The basic cryptologic systems used by the military, the diplomatic service and the security services during the period 1941-45 were the following:

1). The Soviet military used 2, 3, 4 and 5-figure codes enciphered with substitution methods or with additive sequences. The latter method was reserved for the most important 4 and 5-figure codes.

2). The People's Commissariat for Internal Affairs - NKVD also relied on figure codes enciphered both with substitution and addition methods.

3). Partisan groups used figure codes enciphered with additive sequences or transposed based on a key word.

4). The diplomatic service had a 4-figure codebook enciphered with one time pad tables plus an emergency system.

5). The agents of the foreign intelligence service that did not have diplomatic cover and the Communist International mostly used a simple letter to figure substitution table to encode a message and this was further enciphered by using a book and the aforementioned conversion table to create additive sequences.

6). Internal radio traffic between factories and the People's Commissariats of heavy industry, tank production, engineering etc was sent both unenciphered, enciphered with simple cover words or with figure codes and with one time pad tables.

7). According to the available sources the Soviet Union relied almost entirely on hand methods for enciphering its important communications. A small number of cipher machines were available but it doesn’t seem that they were used widely during the war. The known types were the K-37 ‘Crystal’ (Soviet copy of the Hagelin B-211) and the cipher teleprinters B-4 and M-100. 

8). Voice communications were protected by the EU-2 speech scrambler and the Cobol P device.

9). A cipher device was used on radio fax transmissions.

Military codes

TICOM reports DF-196 ‘Report on Russian decryption in the former German Army’, DF-112 ‘Survey of Russian military systems’, DF-292 ‘The Cryptologic Service in WWII (German Air Force)’ (4), IF-175 ‘Searbourne Vol. XIII, PT. 2’, I-120 ‘Translation of Homework by Obltn. W. Werther, Company Commander of 7/LN Rgt. 353, written on 12th August 1945 at A.D. I. (K).’ and I-19 a-g ‘Report on Interrogation of KONA 1 at Revin, France, June 1945’ give a summary of the main military cryptosystems (3).

The basic systems were 2, 3 and 4 figure letter/word to figure substitution tables used either unenciphered or enciphered with similar substitution tables. The 2 and 3 figure code tables were used by frontline units, while the 4-figure codes were used at division level and above.

Examples of 2 and 3 figure tables (4):

Regarding the 4-figure traffic, up to 1942 a 4-figure codebook OKK (General Commander’s Code) was used. The codebook had 50 pages of 100 groups each for a total of 5.000 code groups, arranged alphabetically (5). 

In the period 1939-1942 the codes OKK-5, OKK-6, OKK-7 and OKK-8 were used.

Encipherment was by means of substitution tables.

In mid 1942 the use of the OKK codes was discontinued and instead units were given authorization to create their own 4-figure substitution tables called SUW/SUV. Based on guidelines from the Army’s cipher department each unit had permission to create its own 4-figure code table and the enciphering method.

Examples of SUV tables (6):

For the highest level communications a 5-figure codebook was used, enciphered with additive tables called ‘Blocknots’. There were two main types of tables, the ‘General’ (31 pages with each page having 300 5-digit groups – each page was valid of 1 day regardless of the messages sent) and the ‘Individual’ (50 pages with each page having 60-120 5-digit groups - each additive group could only be used once).

In the period 1939-1945 the following 5-figure codes were used:

OPTK-35, OK40, K1, 0-11A, 0-23A, 0-45A, 0-62A and 0-91A.

Example of 5-figure code encipherment (7):

NKVD codes

The NKVD used procedures similar to the Army’s. At the top level an enciphered 5-figure code was used. Several large 4-figure codes (up to 10.000 groups) enciphered with additive tables were also used at a high level. Frontline units used small codebooks (approximately 2.500 values) and code tables similar to the Army’s. (8)

Example of NKVD code table (9):

Partisan codes

The Soviet partisans used various enciphering procedures in their radio communications with Moscow. These ranged from simple Caesar ciphers to double transposition, transposition using a stencil and Caesar ciphers enciphered with additive (including one time pad).

Examples of partisan codes (10):

Diplomatic codes

The Soviet diplomatic service used a 4-figure codebook enciphered with one time pad. In addition there was an emergency cipher procedure for consulates that did not have access to new enciphering tables.

Foreign intelligence and Comintern codes

Soviet agents operating ‘illegally’ (with no diplomatic cover) did not have access to a regular supply of enciphering tables so they had to memorize a simple letter to figure conversion table and use it to encode their messages. Then they could also use this table for encipherment by using a prearranged book as a ‘key’ generator. Passages from the book would be taken, the letters would be converted into numbers through the conversion table and this numerical sequence would be used to encipher the message (addition without carrying over the numbers).

The same basic system was used by Communist Parties in their communications with Moscow. A codebook or conversion table would be used to encode the message and a random book would provide the additive sequences as above. (11)

Internal radio traffic

Radio communications between factories, State authorities, civil aviation and military units in the Soviet interior were sent plaintext, encoded with a simple system, using 3 or 4 figure substitution codes or with the Army’s 5-figure code and one time pad tables.

German solution of Soviet codes in WWII

The German intercept organization in the East

Codebreaking and signals intelligence played a major role in the German war effort. Army and Luftwaffe units relied on signals intelligence in order to monitor enemy units and anticipate major actions.

In the period 1941-45 the Army had 3 signal intelligence regiments (KONA units) assigned to the three Army groups in the East (KONA 3 for Army Group North, KONA 1 for South and KONA 2 for Centre). There was also NAA 11 - Signal Intelligence Battalion, providing intelligence to the German forces in Finland. This unit exchanged results with the Finnish codebreakers.

In 1942 another KONA unit was added to Eastern front and from 1943 mostly monitored Partisan traffic, this was KONA 6.

The Luftwaffe had similar units assigned to the 3 Air Fleets (Luftflotten) providing aerial support to the Army Groups. These were the 1st Battalion of Luftnachrichten Regiment 1 (assigned to Luftflotte 1), Signal Intelligence Battalion East (assigned to Luftwaffenkommando Ost, later renamed Luftflotte 6) and 3rd Battalion of Luftnachrichten Regiment 4 (assigned to Luftflotte 4).

The Air Signal Battalions (Luftnachrichten Abteilung) were later subordinated to Air Signal Regiment 353.

Army and Luftwaffe signals intelligence units cooperated closely and exchanged results on a daily basis.

Both the Army and the Luftwaffe established central cryptanalytic departments for the Eastern front. The Army’s Horchleitstelle Ost (later renamed Leitstelle der Nachrichtenaufklärung) was based in East Prussia and worked on Soviet military and NKVD 2, 3, 4 and 5-figure codes. Additional work on the high level 5-figure code was carried out at Referat 5 of Inspectorate 7/VI, in Berlin.

At the Luftwaffe’s Chi Stele Soviet codes were worked on by Referat E1, headed by Edwin von Lingen. 

The signal intelligence regiments had fixed and mobile intercept units plus a small cryptanalytic centre called NAAS (Nachrichten Aufklärung Auswertestelle - Signal Intelligence Evaluation Center). Although they were subordinate to Horchleitstelle Ost, in practice they had significant autonomy on the traffics they chose to cover (12). The task of the field units was to exploit current enemy cryptosystems using the material given to them by their NAAS units and by HLS Ost. New cipher procedures were not supposed to be handled by forward units but instead they were tackled by HLS Ost and the NAAS units. Important Soviet codes such as the Army’s enciphered 5-figure code and the NKVD cryptosystems were handled solely at HLS Ost and by the central department in Berlin.

Apart from the Army’s Inspectorate 7/VI and the Luftwaffe’s Chi Stelle several other organizations also worked on Soviet codes. The Navy’s signal intelligence agency B-Dienst – Beobachtungsdienst had intercept units in the Black Sea and in the Baltic, the Signal Intelligence Agency of the Supreme Command of the Armed Forces OKW/Chi had a Russian department under professor Novopaschenny that worked on the 5-figure code, the Forschungsamt intercepted traffic from the Soviet interior (mostly of economic content), the Foreign Ministry's deciphering deparment Pers Z solved Comintern codes and the Army’s Ordnance, Development and Testing Group, Signal Branch – Wa Pruef 7  Group IV section C intercepted Soviet multichannel radio-teletype traffic from inside the Soviet Union.

The German Allies in the East (Italy, Hungary, Romania) did only limited work on Soviet codes. The exception to this rule was Finland, whose codebreaking department had been solving Soviet codes since the 1930’s and continued to do so up to 1944. Relations between Finnish and German codebreakers were close and they exchanged information on important systems.

Overview of German codebreaking successes

The communications of the Soviet Union were a major target of the German codebreakers during the interwar period and several military systems had been solved up to the 1941 invasion (13). The exploitation of these codes from an early date allowed the Germans to follow changes and improvements in Soviet procedures, as simple systems used in the 1920’s and 1930’s were replaced with more complex ciphers. Also the Soviet-Finnish war of 1939-40 served as a training exercise for the German signal intelligence organizations since ample radio traffic from actual fighting units could be intercepted and examined. The occasional mistakes made by Soviet cipher clerks, the large volume of traffic and the cipher material captured by the Finns and shared with the Germans contributed to the solution of most of the Soviet enciphered traffic, including the Army’s high level 5-figure code (14).

In the period 1941-45 the German signal intelligence agencies continued to exploit a large part of Soviet military and NKVD 2, 3 and 4 figure codes and even succeeded in solving some of the 5-figure traffic.

Limits of available sources

Unfortunately the files of many of the organizations intercepting and exploiting Soviet codes were either destroyed in WWII or are still classified by the NSA. However the material released to the US, UK and German archives in the last decade is sufficient for evaluating the general performance of German signals intelligence in the Eastern front.

The most reliable sources are the monthly reports of Referat 5 and of Horchleitstelle Ost, which are included in the War Diary of Inspectorate 7/VI. These are available for the first half of 1941, for the period 1942-43 but not for January to September 1944 or for the period July 1941 – January 1942 (at least I haven’t been able to find them).

Soviet Army and Airforce codes

The Army’s Inspectorate 7/VI and the Luftwaffe’s Chi Stelle intercepted and decoded Soviet communications through their forward units and from fixed stations in the East. Forward units were supposed to exploit systems that had already been identified and solved. On the other hand new traffic and difficult high level systems were tackled at the cryptanalytic centre Horchleitstelle Ost/ Leitstelle der Nachrichtenaufklärung in East Prussia.

This arrangement meant that field units could process a lot of messages each month without the need for specialized personnel and the results were quickly communicated to the armed forces. According to TICOM report I-19 (15) the estimated monthly average for KONA 1 (assigned to Army Group South) in 1944 were 5.500 cipher, 6.000 clear text and 500 practice messages for a total of 12.000. The systems exploited by field units were 2, 3 and 4-figure codes. The NKVD systems and the Army’s 5-figure code were processed at HLS Ost.

The monthly reports of HLS Ost, together with TICOM reports written by personnel assigned to work on the solution of Soviet codes show that Soviet military 2, 3 and 4-figure codes were continuously read, with new systems being solved each month. Soviet AF traffic seems to have been easier to solve than the Army’s since more traffic was generated daily as the air units had to use the radio much more often than their Army counterparts.

Prior to the 1941 invasion the Luftwaffe’s Chi Stelle could solve the majority of intercepted Soviet codes (16). The Army agency could also exploit the majority of systems but it was hampered by lack of personnel and the processing of the 5-figure code was slow due to the limited number of messages intercepted daily (17). Still the reports say that the information from signals intelligence was extremely valuable to the General Staff.

Report of period Jan-Mar 1941:

Report of 10 June 1941:

Things changed in the summer of 1941 when due to the military operations the Soviet communication system broke down, leading to mistakes in encipherment and in addition codebooks were captured by the Germans. This led to the solution of even the high level Soviet communications, carried out between the General Staff and the Fronts. A summary from August 16 1941 says that since the beginning of the war with Russia (ie, for a period of about 2 months) 69 cipher procedures had been resolved and one of the greatest successes of the unit included the solution of the 5 figure additive procedure RC 130, which could be read already 6 days after the war started. This system was used by the Soviet General Staff and conveyed information on the most important commands and operational messages.

Report of 16 August 1941:

According to Army cryptanalyst dr Buggish, the Soviet 5-figure system OK40 (Operational Code 40) was exploited in the summer of 1941. This was a codebook with 25.000 entries enciphered with a 300 5-figure group additive table. The codebook was captured at the start of the campaign and the tables were reused thus facilitating solution. A characteristic of the system that was exploited by the German codebreakers was that the first 3 figures of the codegroups were either all odd or all even (18).

The files I have do not include the reports of HLS Ost for the second half of 1941 or January 1942 but the report from February shows that the 5-figure code could still be exploited revealing orders for operations, situation reports, reconnaissance reports, information on troop movements, inventory of ammunition and food, reports of desertion etc

Report of HLS Ost - February 1942

In the first half of 1942 use of the 5-figure codes started to expand, reaching roughly 50% of intercepted traffic. Also a new 5 figure code 023-A replaced the previous 011-A (used in 1941 and early 1942). The codebreakers of HLS Ost were able to solve 5-figure traffic in this period but the use of ‘Individual’ additive pads for a lot of the traffic meant that the analysis of this material had to be undertaken at headquarters in Berlin, using the IBM/Dehomag punch card equipment in order to find repeats.

Also in 1942 the widely used Army 4-figure codebook OKK was replaced with a large number of SUV substitution tables. Although the security of such a system was not very high the use of different SUV tables by each unit meant that solution depended on the amount of material received and on operator errors.

In 1943 the reports of HLS Ost show that apart from 2, 3 and 4 figure codes also traffic from the Soviet interior was intercepted and solved.

Report of July 1943

The high level 5-figure traffic was using mainly ‘Individual’ additive pads, so only a small number of messages seem to have been read. Also in 1943 the new 5 figure code 045-A was used till midyear. Then the 062-A was used by the Army.

The reports of January-September 1944 are missing but those of October ’44 - March ’45 show that military codes continued to be solved. The new 5-figure code 091-A could only be read in rare cases.

Reports of Referat 2 - October 1944

Soviet Navy codes

The German Navy’s signal intelligence agency B-Dienst monitored the Soviet naval traffic in the Black Sea, the Baltic and the North Sea. Low level systems used by small ships were continuously read and high level 4-figures codes could also be exploited till late 1943. An important success for the German side was the solution of the simple codes used by Soviet naval aircraft in the North Sea. This traffic carried important information on the convoys between the UK and the SU. Thanks to this information the Germans were able to inflict significant losses on these convoys.

NKVD codes

The People's Commissariat for Internal Affairs - NKVD was a huge organization tasked with foreign intelligence, internal security, border security, railroad security and overview of the state run economy. The communications of such an important organization were targeted by the German codebreakers and traffic from NKVD border units could be read in the 1930’s (19).  During WWII there was a separate department at Horchleitstelle Ost for NKVD traffic.

NKVD codes were extensively read, not only 2 and 3-figure codes used by frontline units but also several large 4-figure codebooks used by higher authorities (GUP NKVD-General Directorate of Border and internal security and Front staffs).

By reading these communications the Germans got intelligence on the operations of the NKVD border units, the conditions in the Army’s rear areas were the NKVD was responsible for security, intelligence operations, railway shipments and even reports on the Soviet economy.

The reports of HLS Ost list many NKVD systems solved in 1942, 1943 and 1944. For example in April ’42 5-figure traffic was solved (since the NKVD also used the army’s 011-A and 023-A codes) and the code N.17 of the 23rd NKVD Railway division. 

In June 1942 the codes 06-P and N.14 are mentioned:

In January the new code 010-P was solved after discovering the enciphering procedure.

In the same period the important RC 1100 code (original name 039W) was investigated and code values recovered. Report of June ’43

In July the code of NKVD counterintelligence RC 1500 was read revealing operations against German parachutist agents.

In August the fourth main NKVD cipher procedure RC 1510 was listed as solved and in September work on the NKVD 4-figure methods RC 747, RC 1100, RC 1500, RC 1510 was making good progress. In the same month the NKVD railway code RC 1560 could be read continuously.

NKVD codes continued to be read with success up to end 1944 since these systems seem to have remained in use for long periods of time. For example the Germans expected that the important RC 1100 code of 10.000 values would be changed in January 1944, thus negating their efforts to solve it. However their report of October 1944 says that it was only replaced in September ‘44.

Partisan codes

Partisan codes were investigated by Inspectorate 7/VI’s Referat 12 (Agents section) in 1942 and by signal intelligence regiment 6 -KONA 6 in the period 1943-44.

The reports of Referat 12 for the second half of 1942 show that partisan communications were monitored and the different types of traffic were classified by the cipher system used. However, apart from a few spy cases, actual traffic was not solved.

List of Russian agents and partisans traffics from October 1942:

In 1943 KONA 6 was assigned to cover partisan traffic and from summer 1943 some of it could be read. The results were communicated to the security services like the Abwehr so that enemy agents could be apprehended and partisan operations thwarted.

Comintern codes

The codes of the Comintern were read by the Foreign Ministry's deciphering department Pers Z. According to Adolf Paschke (20), head of the linguistic cryptanalysis department, different books were used in order to create cipher sequences and encipher the underlying code but thanks to human error it was possible to solve these and identify the books used. Apparently the personnel that were responsible for enciphering messages had the tendency to reuse specific passages from the books thus compromising the whole system. Paschke said that ‘A particular instance deserves mention. It concerns telegraphic material of a total length of about two million digits. In the course of the work of solution it was established that it had been enciphered by means of five books which gave an encipherment sequence of about 5 million digits. An apparently hopeless case. And yet solution was achieved’.

Diplomatic codes

The Soviet diplomatic service used a 4-figure codebook enciphered with one time pad tables. In the Far East a simpler procedure was also used, probably due to the lack of new enciphering tables. According to German accounts they monitored Soviet diplomatic traffic but could not solve messages due to the use of one time tables.

Internal network

State ministries, factories and military units in the Soviet interior relied on radio communications for a lot of their traffic because the landline network was not fully developed to cover the huge areas of the Soviet Union.

1). Economic traffic between factories was intercepted and solved by the Forschungsamt (21). According to Paetzel (head of department 6 - Cipher Research), traffic from the SU averaged several hundred messages per day and was mostly plaintext with cover words. The chief evaluator Seifert said: ‘Our greatest success was obtained on Internal Russian traffic which enabled us to discover the various bottlenecks in the Russian supply organization’. According to a report on the Forschungsamt some 20-30 multi-channel radio teletype links were monitored (22). 

A British report on the Forschungsamt says that the communications of several Soviet Commissariats (tank industry, munitions, machine tools etc) were read (23):

Internal Soviet radio traffic was also intercepted and evaluated by the German Army from a base in Staats, Germany (operated by the Army Ordnance, Development and Testing Group, Signal Branch Group IV C  -  Wa Pruef 7/IV C ) and by Group VI (OKH/GdNA Group VI) stationed in Loetzen, East Prussia.

According to the report FMS P-038 ‘German radio intelligence’ (24):

Strategic radio intelligence directed against the Russian war production effort provided a wealth of information for the evaluation of Russia's military potential. Owing to the general dearth of long-distance telephone and teletype land circuits, radio communication assumed an especially important role in Russia not only as an instrument of military leadership but also as the medium of civilian communication in a widely decentralized economy. In keeping with its large volume, most of this Russian radio traffic was transmitted by automatic means, as explained in Appendix 7. The German Army intercepted this traffic with corresponding automatic equipment and evaluated it at the communication intelligence control center. Multiplex radioteletype links connected Moscow not only with the so-called fronts or army groups in the field, but also with the military district headquarters in Leningrad, Tiflis, Baku, Vladivostock, and in many other cities. In addition, the radio nets used for inland navigation provided an abundance of information. Although this mechanically transmitted traffic offered a higher degree of security against interception, the Russians used the same cryptosystems as in the field for sending important military messages over these circuits. The large volume of intercepted material offered better opportunities for German cryptanalysis. Strategic radio intelligence furnished information about the activation of new units in the zone of interior, industrial production reports, requests for materiel and replacements, complaints originating from and problems arising at the production centers and administrative agencies in control of the war economy. All this information was indexed at the communication intelligence control center where reports were drawn up at regular intervals on the following aspects of the Russian war production effort:

Planning and construction of new factories;

Relocation of armament plants;

Coal and iron ore production figures;

Raw material and fuel requirements for industrial plants;

Tank and gun production figures;

Transportation facilities and problems;

Railway, inland shipping, and air communications;

Agricultural production;

Food distribution and rationing measures;

Manpower, labor allocation, and other relevant matters.

Strategic radio intelligence thus made a slight dent in the Iron Curtain, which during the war was drawn even more tightly than at present, and offered some insight into the operation of the most distant Siberian production centers and the tremendous war potential of that seemingly endless expanse of land.

In the period 1942-45 the analysts of the German Army’s Leitstelle der Nachrichtenaufklärung evaluated this material and issued economic reports based on the intercepted radio traffic (25).

2). The Aeroflot (civil aviation network) 3 figure code was read by Army codebreakers since summer 1943.

Report of June ’43:

This traffic had interesting information on the organization of Aeroflot, the movement of men and supplies to the front, fuel supplies and the training of new pilots (26). 

3). Apart from standard radio communications there were also multichannel radio teletype devices being used. The Germans were able to intercept these transmissions automatically and print the text. Economic traffic was often sent plaintext while military communications used 3, 4 and 5 figure codes. The 3 and 4 figures could be read.

Cipher machines

At this time there is very limited information on WWII era Soviet cipher machines.

1). The Germans captured a K-37 machine in the summer of 1941, examined it and came up with methods of solution. However during the war they did not intercept any messages enciphered on this device, so it seems that it was not used in the Western areas of the SU.

2). Apart from the K-37, two cipher teleprinters were identified by the Germans. Both seem to have had 6 wheels with five enciphering the respective Baudot impulses while the sixth controlled their movement. The device solved by the Forschungsamt was used on 2-channel networks and had 6 wheels that stepped regularly. During pauses the device enciphered the Russian letter П seven times in succession and this flaw was used to solve the device and recover the daily settings (pin arrangement of the wheels). This success however turned out to be short lived since in late 1943 the Soviet cipher machine was modified and no pure ‘key’ was transmitted during transmission pauses. It seems that from then on this traffic was only examined by the Army’s Inspectorate 7/VI (27).

Regarding the second device the war diary of Inspectorate 7/VI shows that the traffic was continuously examined and some progress was made thanks to operator errors and a flaw in the construction of the machine (28). This device was used on communications links between Moscow and the Army Fronts. There were only about 10 links overall with ~8 for the Army and ~2 for the Airforce (29). Although the machine was not ‘broken’, messages in depth could be decoded and they contained reports on Soviet and German military dispositions, , statements by POW's, signal intelligence reports, reports for TASS and SOVINFORMBUREAU, letters concerning postings, transfers, promotions, weather situation reports and supply manifests (30).

3). Radio fax transmissions were intercepted and decoded, however no information is available on the type of cipher device used on this traffic by the Soviets. The traffic contained hand-written communications, typewritten texts, drawings, weather maps, technical diagrams and charts. 

4). Speech privacy systems were used for radio telephone conversations between Moscow and various cities such as Leningrad, Irkutsk, Alma Ata and Chelyabinsk. The Germans were able to solve the first Soviet device but no information is available on the traffic they intercepted or its contents. The second device introduced during the war was more secure and although German specialists identified it as a Tigerstedt system (time division scrambling) it was not ‘broken’.

Failures of Soviet cipher security

The Soviet Union had failed to secure its sensitive communications during the 1920’s and 1930’s. In 1920 the victory of the Poles over the Red Army in the battle of Warsaw owed a lot to the work of their codebreakers. In the 1930’s Soviet military codes were read by the Japanese in the East and by the Finns during the Winter war.

In 1941 the sudden German attack destroyed a large part of the Soviet military and their communications system collapsed. The loss of trained radio operators and of cipher material meant that Soviet communications were extensively read by the Germans. Moreover the new hastily trained radio operators could not avoid making mistakes and thus compromising the security of otherwise secure systems.

However the widespread use, during the war, of 2, 3 and 4 figure code tables enciphered with substitution methods was a mistake considering that they could only offer limited security. Especially for the 4-figure mid and high level communications a more secure procedure should have been adopted. Obviously the fact that they could be easily used by hastily trained personnel must have played a role in this case.

Another lost opportunity was the lack of a secure cipher machine for widespread usage among the armed forces. Such a device would have a allowed a large volume of traffic to be sent quickly and securely. The Soviets used cipher machines in very small numbers and only in a handful of communication links. 

Other mistakes noted by the Germans were that the operational plans of units using secure procedures were compromised by smaller units supporting them such as artillery, rocket launcher, heavy mortar and engineers since these did not use secure procedures.

The NKVD was guilty of using insecure codes and also of keeping their codebooks in use for long periods of time, thus making the work of the German codebreakers much easier.

The biggest failure of the Soviet cipher departments was their unwillingness to acknowledge their failures and introduce new secure procedures. According to Anatoly Klepov (31), in the postwar era there was an evaluation of Soviet cipher security during WWII and although it was acknowledged that their codes had been compromised the final report hid this fact in order to protect the reputation of Lavrentiy Beria, head of the NKVD.

This mistake meant that outdated codes and procedures continued to be used in the immediate postwar period and they were exploited by Anglo-American codebreakers in the years 1945-48, when they managed to solve many important Soviet cryptosystems, including the top level cipher teleprinters.

Conclusion

The use of signals intelligence and codebreaking by the Germans and Soviets in the Eastern front is a subject that has received very little attention by historians so far. The main reason was the lack of adequate sources. The archives of the Soviet codebreaking organizations remain closed to researchers but in the last decade many important documents on German signals intelligence operations have been released to the public archives.

From these documents it is clear that the Germans invested significant resources in their signal intelligence agencies and relied on their output during the fighting in the East. Against an opponent that outnumbered them in men and war materiel (tanks, planes, artillery) signals intelligence gave them the opportunity to monitor enemy movements and make efficient use of their limited resources.

The cryptologic systems used by the Soviet Union at low and mid level were extensively compromised during the war and in 1941-42 even their high level 5-figure code could be read. In the period 1943-45 the use of one time pad in enciphering their 5-figure code secured this system but other important codes could be read including the systems of the NKVD.

The report FMS P-038 ‘German radio intelligence’ says ‘In the Russian theater the mass of minute details assembled by German communication intelligence over a period of years provided a clear, reliable, and almost complete picture of the military potential, the strategic objectives, and the tactical plans of the most powerful enemy which the German Army had ever encountered. The results were far superior to those obtained during World War I’.

Considering the countless enemy cryptosystems solved by the Germans during the period 1941-45 (military, NKVD, partisan, economic) this statement does not appear to be an exaggeration.

Notes:

(1). Journal of Contemporary History article:  ‘Spies, Ciphers and 'Zitadelle': Intelligence and the Battle of Kursk, 1943’, 249

(2). Soviet cryptologic history, The cryptographic front, On the history of cryptography in Russia

(3). DF-112, pages 129-165, DF-292, pages 53-86, I-120 ‘Translation of Homework by Obltn. W. Werther, Company Commander of 7/LN Rgt. 353, written on 12th August 1945 at A.D. I. (K).’

(4). DF-292, p 54-55 and DF-112, p129-30

(5). DF-112, p151-52

(6). DF-112, p143-44, p153-54

(7). DF-112, p157

(8). Reports of HLS Ost

(9). DF-112, p155-56

(10). DF-112, p158-63

(11). DF-111, p9

(12). DF-112, p115

(13). DF-112, p170-86

(14). IF-175 ‘Searbourne Vol. XIII, PT. 2’, p23 and I-120 ‘Translation of Homework by Obltn. W. Werther, Company Commander of 7/LN Rgt. 353, written on 12th August 1945 at A.D. I. (K).’, p39-42

(15). I-19b, p44

(16). DF-292, p24-29

(17). Reports of Referat 5 January-June 1941.

(18). TICOM I-176, p2 (note that according to TICOM I-120, p39 it was the last 3 digits that were all odd or all even)

(19). DF-112, p7-22

(20). DF-111, p8-9

(21). TICOM I-25, p2-5

(22). TICOM DF-241 ‘The Forschungsamt’ Part IV, p36

(23). HW 40/186 ‘Activities of the Reichsluftfahrtministerium Forschungsamt’

(24). FMS P-038 ‘German radio intelligence’, p123-124

(25). CIA FOIA: Soviet Union military economic reports - German

(26). TICOM I-116, p2 and TICOM I-173, p12

(27). Soviet cipher teleprinters of WWII

(28). TICOM I-153, p3: ‘In Autumn 1944 both the end of 'adder' and every pause in the cipher proper was preceded by seven key letters [redacted]. Then the traffic went off the air and reappeared in December with no external change except that the seven ‘residue' letters had been reduced to three, suggesting a modification of the machine.

(29). TICOM I-153, p2

(30). TICOM I-169, p25

(31). “The historical truth” of Beria and Suvorov about cryptography and radio intelligence