The American M-209 cipher machine

At the start of WWII, the US armed forces used various means for enciphering their confidential traffic. At the lowest level were hand ciphers. Above that were the M-94 and M-138 strip ciphers and at the top level a small number of highly advanced SIGABA cipher machines.

The Americans used the strip ciphers extensively however these were not only vulnerable to cryptanalysis but also difficult to use.  Obviously a more modern and efficient means of enciphering was needed.

At that time Swedish inventor Boris Hagelin was trying to sell his cipher machines to foreign governments. He had already sold versions of his C-36, C-38 and B-211 cipher machines to European countries. He had also visited the United States in 1937 and 1939 in order to promote his C-36 machine and the electric C-38 with a keyboard called BC-38 but he was not successful (1). The Hagelin C-36 had 5 pin-wheels and the lugs on the drum were fixed in place. Hagelin modified the device by adding another pin-wheel and making the lugs moveable. This new machine was called Hagelin C-38 and it was much more secure compared to its predecessor.

In 1940 he brought to the US two copies of the hand operated C-38 and the Americans ordered 50 machines for evaluation. Once the devices were delivered, they underwent testing by the cryptologists of the Army’s Signal Intelligence Service and after approval it was adopted by the US armed forces for their midlevel traffic. Overall, more than 140.000 M-209’s were built for the US forces by the L.C. Smith and Corona Typewriters Company. (2)

The American version of the Hagelin C-38 was called Converter M-209 by the Army and USAAF and CSP-1500 by the Navy. Compared to the original version it had a few modifications. The M-209 had 27 bars on the drum while the C-38 had 29. Another difference was that the letter slide was fixed. During operation the text was printed by setting the letter spindle on the left to the desired letter and then turning the hand crank on the right.

The M-209 was a medium-level crypto system used at Division level down to and including battalions (Division-Regiment-Battalion) (3) and even up to Corps for certain traffic. The USAAF used it for operational and administrative traffic and the Navy aboard ships. SIGABA was used for higher level messages (Army-Corps-Division) and hand systems like Slidex and the Division Field Code used for tactical messages (Battalion-Company-Platoon).

The Germans called it ‘AM 1’ (Amerikanische Maschine 1) and the Japanese ‘Z code‘.

The missing NAAst 5 reports

Although I’ve given up on getting these files (for reasons that have already been mentioned) I will post this information in the hope that someone else will succeed.

At the US national archives, in the NSA transfer group TR-0457-2016-0017, box 45, folder 3953 there is a file titled ‘KOMMANDEUR DER NACHRICHTEN AUFKLARUNG 5, 1944 (S-013,494)’.

It is possible that this file contains the missing NAASt5 reports. Maybe someone can get hold of this file and solve the mystery.  

TICOM report DF-217

I’ve uploaded TICOM report DF-217 ‘Russian cipher device K-37’, written by dr Grimmsen. 

Also added a summary and pics in The Soviet K-37 ‘Crystal’ cipher machine.

TICOM DF-196

The NSA FOIA/MDR office has declassified the TICOM report DF-196 ‘Report on Russian decryption in the former German Army’.

Google drive link

TICOM report D-83 ‘Summary of Work Done on Typex Traffic by OKH/In 7/VI, 1939-1941’

Uploaded at arcre.com

Essay by Frode Weierud on Inspectorate 7/VI cryptanalyst

Who was Harry Welsch?

Candle in the Dark: COMINT and Soviet Industrial Secrets, 1946-1956

The study ‘Candle in the Dark: COMINT and Soviet Industrial Secrets, 1946-1956’ by Carol B. Davis is available for download from the NSA website.

This version (unlike the copy at the Cryptologic Museum’s Library) is complete!

Information on the Enigma cipher machine found in the War Diary of Inspectorate 7/VI

During WWII the German Army made extensive use of signals intelligence and codebreaking in its operations against enemy forces. German commanders relied on signals intelligence in order to ascertain the enemy’s order of battle and track the movements of units.

The German Army’s signal intelligence agency operated a number of fixed intercept stations and also had mobile units assigned to Army Groups. These units were called KONA (Kommandeur der Nachrichtenaufklärung - Signals Intelligence Regiment) and each had an evaluation centre, a stationary intercept company, two long range signal intelligence companies and two close range signal intelligence companies.

The KONA units did not have the ability to solve complicated Allied cryptosystems. Instead they focused on exploiting low/mid level ciphers and even in this capacity they were assisted by material sent to them by the central cryptanalytic department in Berlin. This was the German Army High Command’s Inspectorate 7/VI. 

The War Diary of Inspectorate 7/VI

Some files of the German army signal intelligence service survived WWII and were retrieved in 1947 from a camp in Glasenbach, Austria, where they had been buried at the end of the war.

The War Diary of Inspectorate 7/VI for the years 1939-45 can be found in the US National Archives, in collection RG457 and in the TICOM collection of the German Foreign Ministry’s Political Archive.

The reports of departments 1, 7, 13 and F occasionally have information on the Enigma cipher machine (both commercial and plugboard versions).

Initially department 1 was responsible for general cryptanalytic research but in 1941 department 7 was created to look into the security of German cipher systems. For a time both 1 and 7 did general crypto research. In November 1942 department 13 was created and from then on department 7 dealt solely with German hand systems, while department 13 was responsible for German cipher machines. In 1943 department F (Forschung/Research) was created to do general cryptanalytic research.

I’ve copied the relevant passages from the War Diary and used google translate. However many terms were not translated correctly so it was up to Frode Weierud, an expert on Enigma history, to correct these passages.

Thus I present the War Diary entries dealing with the Enigma machine for the years 1941-45 (I’m afraid I don’t have the files of 1939-40):

The compromise of Greek partisan radio communications in WWII

A history lesson

At the start of WWII the Kingdom of Greece, ruled by Ioannis Metaxas  (head of the 4th of August Regime) followed a neutral foreign policy and tried to avoid taking part in the conflict. However constant Italian harassment and provocations (such as the sinking of the cruiser Elli) and the transfer of Italian army units to Albania made it clear that war could not be avoided for long.

In October 1940 Italian forces invaded Greece, in the area of Epirus, and the Greek-Italian war started. The Greek forces were able to contain the assault and the Greek counterattack forced the Italians back into Albanian territory. After the defeat of a major Italian offensive in spring 1941 the front stabilized inside Albania.

At the time Britain was overextended with obligations in Europe, Middle East and Asia. However the British armed forces made a small contribution with an RAF expeditionary corps. When more British forces started to arrive in March 1941, their involvement gave Germany an excuse to become involved in the conflict.

German forces invaded Greece in April 1941 and made rapid progress due to the fact that almost the entire Greek Army was fighting in the Epirus area. The remaining units and the small British forces transferred to Greece in March-April 1941 were unable to stop them. Then in May 1941 the Germans were also able to defeat the Greek and British forces that had retreated to the strategic island of Crete.

In the period 1941-44 Greece was split into three occupation zones, controlled by Italy, Germany and Bulgaria.  This measure fractured the Greek economy and together with hyperinflation and loss of value of the paper currency led to the collapse of the economy.

Greece was a poor agricultural country prior to WWII. The war of 1940-41, the splitting of the country into three occupation zones and the confiscation of goods by the occupying powers led to the impoverishment of an already poor population.

Greek resistance groups

Under these circumstances several resistance groups were formed by Greek patriots in order to oppose the Axis powers.

Small groups operated in urban centers but the bigger ones could only survive in the countryside where the presence of Axis troops was limited.

The main ones were the military wing of the Greek Communist Party - ELAS (Greek People's Liberation Army) and the liberal EDES (National Republican Greek League).

The resistance forces organized by the Communist Party were ostensibly created in order to oppose the Axis rule and liberate Greece but in reality their main goal was to eliminate their liberal rivals, unify all resistance groups under communist control and gain power in postwar Greece (1).

During the period 1943-44 the Communist forces showed more interest in attacking and destroying other resistance groups than in attacking the occupiers. One of their most infamous acts was the destruction of the EKKA (National and Social Liberation) resistance group and the execution of its commander Dimitrios Psarros.

The ΕΑΜ ELAS movement grew in power during the occupation for several reasons. Compared to the other resistance groups it had an advantage in that it was tightly controlled by the Communist Party, an organization that knew how to operate in adverse conditions. The main achievement of the communists was that they managed to get British backing for their operations. British liaison officers were transported to Greece and British money and arms supported the ΕΑΜ ELAS movement.

In addition to British support, with the collapse of Italy in September 1943, several Italian military units in the Balkans surrendered to the partisans and the capture of their heavy weapons (mortars, artillery, machine guns) gave ΕΑΜ ELAS the ability to conduct regular military operations.

Radio communications and ciphers of the ELAS movement

According to German sources ELAS radio communications began to be intercepted by the units of KONA 4 (Kommandeur der Nachrichtenaufklärung - Signals Intelligence Regiment) in early 1944.

KONA 4 was a German Army signal intelligence unit assigned to cover radio traffic from the Balkans and the Middle East. In the period 1943-44 the unit was able to decode a large volume of Yugoslav partisan traffic.

The quarterly reports of the unit for 1944 (2) show that Greek communist radio traffic was worked on by NAZ G (Nachrichten Nahaufklärungszug - Close Range Signal Intelligence Platoon).

The report Ez Bericht 1944/II says that in April 1944 radio traffic of the Greek communist groups from the areas Volos, Lamia and Olympus was intercepted. The messages were sent in 4-figure and 5-letter groups. The first procedure was a letter to figure Caesar cipher and it was discontinued by the end of April. The second procedure was double transposition with the same key used for both cages. Both were solved and 240 messages read.

Elas-Funkverkehr

Mitte April wurde erstmalig ein griechischer kommunistischer Bandenfunkverkehr mit Funkstellen im Raum Volos - Lamia und im Olymp-Gebiet festgestellt. Seither sind hauptsächlich zwei Arten von Chisprüchen der Elas (Griechisches Volksbefreiungsheer)- Verkehre angefallen: 4Z- und 5B-Sprüche.

a) 4Z-Sprüche.

Statistische Untersuchungen des Spruchmaterials ergaben eindeutige Hinweise auf ein mehrfach belegtes 2Z-Cäsar-Verfahren, das in seinen verschiedenen Schlüsselformen durch 4Z-Kenngruppen bezeichnet wird. Es wurden schliesslich fünf derartige 2Z-Buchstaben-Silben-Cäsaren gelöst. Bereits Ende April wurde dieses Verfahren ausser Kraft gesetzt.

b) 5B-Sprüche. 

Die in grösserem Umfange zwischen dem Obkdo. der Elas und der Gruppe der Divisionen Makedoniens mit ihren unterstellten Einheiten abgesetzten 5B-Sprüche wurden als Klartext-Verwürfelungen erkannt. Untersuchungen auf einfache Verwürfelungen waren erfolglos. Erst als zwei nahezu textgleiche Sprüche mit gleicher 4Z-Kenngruppe auftraten, von denen der eine die mit einer Spalten-vertauschung versehene Wiederholung des anderen war, konnte die Losung erstellt und der Spruch als Doppelwürfelverschlüsselung gelöst werden. Die folgende Entschlüsselung aller mit dieser Losung verzifferten Sprüche ergab, dass der Verschlüssler beim Obkdo der Elas besonders für volle Würfel eine Vorliebe hat. Diese Annahme bestätigte sich, als festgestellt wurde, dass darüber hinaus sogar qruadratische Würfel vorlagen, für die eine einfache Lösungsmöglichkeit besteht. In arderen Fällen lagen der Verschlüsselung halbquadratische Würfel zugrunde. Solche können gleichfalls gelöst werden, da in zwei Halbzeilen des waagerecht eingetragenen Chitextes oft eine bekannte Unterschrift gefunden werden kann. Unter Ausnutzung dieser Verschlüsselungsschwächen des Gegners wurden bisher 20 Doppelwürfelosungen erstellt.

In der Berichtszeit wurden insgesamt ca 240 Sprüche mitgelesen die wertvolle Aufschlüsse über den organisatorischen Aufbau, die militärische Gliederung und die militärischen Aktionen der kommunistischqp Banden im griechischen Raume gaben.

ELAS radio-traffic

Mid-April radio communications of a Greek Communist gang , with radio stations in the area of Volos - Lamia and Olympus, was detected for the first time. Since then, mainly two kinds of cipher messages in the ELAS traffic (Greek people's Liberation Army) have turned: 4-figure and 5-letter messages.

a) 4-figure messages.

Statistical investigations of the intercepted material gave clear indications of a multiply occupied 2-figure Caesar system, which in its various cipher forms is identified by 4-figure indicator. Finally five such 2-figure letter-syllable Caesars were solved. Already at the end of April this procedure was cancelled.

b) 5-letter messages.

The 5-letter messages, which in larger extent were sent between the ELAS headquarter and the group of divisions in Macedonia with its subordinate units, were recognized as plaintext transpositions. Studies based on simple transpositions were unsuccessful. It was not until two nearly textually equal messages with the same 4-figure indicator group occurred, of which one could be seen as a column swapped repetition of the other, that an answer was found and the message solved as a double transposition. The following decryption of all the enciphered messages with this solution revealed that the cipher clerk at ELAS headquarter had a special preference for complete transposition rectangles. This assumption was confirmed when it was found that it even square transposition templates was used, for which there exist a simple solution. In other cases, the enciphering was based on using half-square transposition templates. Those can equally be solved because in two half-lines of the vertically entered ciphertext one often will find a well-known signature. So far 20 double transposition solutions have been created using these encryption weaknesses of the enemy.

During the period under review a total of about 240 messages were read which gave valuable insights into the organizational structure, the military plans and the military action of the Communist rings in the Greek area.

The report Ez Bericht 1944/III says that double transposition continued to be used in ELAS radio communications. Due to poor cipher practices this system could be solved. In the reporting period about 120 keys were solved and 2.200 messages read.

Elas bewegung

Sämtliche Funkverkehre der Elas-Bewegung im griechischen Raume verwenden nach wie vor die Dopelwürfelverschlüsselung. Aus der bereits im letzten Bericht erwähnten Vorliebe der gegnerischen Schlüssler für volle Würfel hat sich ein gangbarer Weg zur Lösung dieser Doppelwürfel finden lassen. Unter Verwendung bereite bekannter Unterschriften wurden die Würfellosungen gefunden an quadratischen, doppelquadratischen, halb- und viertel-quadratischen Würfeln, ferner an längen- und lösungsgleichen Würfeln und Würfeln mit Spaltenvertauschung, Dass in einer Anzahl von bereits entzifferten Sprüchen auch Hinweise auf neue Losungen gegeben wurden, erleichterte die Entzifferungsarbeit beträchtlich.

Mit ca. 120 Losungen konnten in der Berichtszeit nahezu 2.200 Sprüche mitgelesen werden,

ELAS movement:

All radio traffic of the ELAs movement in the Greek area still uses the double transposition system. From the preference of the enemy cipher clerks for complete transposition squares, as mentioned in the last report, a practical method of solving this double transposition has been found. By using well-known signatures solutions were found for square, double square, half - and quarter square transposition templates, as well as solutions to same length and solution-equal transposition templates and templates with column swapping.

The decipherment work was eased considerably by the fact that a number of already decrypted messages also gave hints about new solutions. With about 120 solutions nearly 2,200 messages could be read during the reporting period.

The last report Ez Bericht 1944/IV says that approximately 50% of the messages were read:

Elas Bewegung

Der griechische Bandenfunk wurde ausschliesslich von NNA Zg G bearbeitet, der sich in der Berichtszeit 2 Monate auf dem Rückzug befand. Im letzten Vierteljahr 1944 wurde als einziges Verfahren der Doppelwürfel verwendet . Ungefähr 50% der angefallenen Sprüche wurden mitgelesen. Für ca. 30 Kenngruppen wurden die Losungen  erstellt.

ELAS movement

The Greek agent radio traffic was processed exclusively by NNA Zg G who, during the reporting period, had already been on the retreat for 2 months. In the last quarter of 1944 the only method used was double transposition. Approximately 50% of the attacked messages were read. Solutions were found for about 30 characteristic groups (indicators).

Dr. Otto Karl Winkler and TICOM report I-170

Additional information on the exploitation of ELAS communications is available from the TICOM report I-170 ‘Report on French and Greek Systems by Oberwachtmeister Dr. Otto Karl Winkler of OKH/FNAST 4’ (dated January 1946).

The report was written by Dr. Otto Karl Winkler, a member of KONA 4. Dr Winkler was in charge of decoding and translating the Greek messages and in pages 4-6 he stated about his work:

The unit moved to BELGRADE in Autumn 1943, thence, in August 1944 to PERNITZ near WIENER NEUSTADT, However, I received a new task in Spring 1944 with the appearance of Greek messages sent by ELAS. In the course of our two year stay in Athens I had been able to learn modern Greek almost perfectly, on the basis of a knowledge of classical Greek and spurred on by love for and interest in Greece. In addition my duties had provided me with a certain experience of cryptography and a good translation technique. Thus I was put in charge of Greek cryptography and was assisted in the actual cryptographic work by Uffz. Diether STROBL from BERLIN, an English interpreter and technical student. I had held the rank of Wachtmeister since Christmas 1943.

Regarding the cipher systems used he also mentions the 2-figure Caesar system and the double transposition cipher. Solution of the latter depended on the poor practices of the ELAS cipher clerks:

Double transpositions are regarded as a secure type of cipher and are therefore used by many British agents. To the best of my knowledge the unit never succeeded in breaking one and only occasional captured material has rendered it possible to read some traffic retrospectively. For the sake of security it is essential to avoid using complete or even square boxes, typical beginnings or endings of messages and constantly recurring addresses and signatures, to use each key as little as possible and as far as possible to have different keys for each box of the pairs The Greeks overlooked all these rules right up to the end, with the result that messages in the same setting and with the same number of groups (Elementeanzahl) cropped up.

The solution of these messages provided valuable information about the organization, personalities and operations of the ELAS partisan forces:

In any case we succeeded in breaking 50 – 60% of the traffic tackled and as important messages were always retransmitted on several links with different keys, we were able to build up an almost complete picture of the build-up, organization and composition of EAM and ELAS, to compile lists of their leading personalities and officers and to inform the competent German political and military authorities in good time about many planned military and political actions, acts of sabotage, ambushes, dynamitings, etc. I can only remember a few details and cannot reproduce examples systematically as the evaluation of the material wan not my job, which consisted only of deciphering, decoding and translating the available material.

Radio traffic of British liaison officers in Greece

Apart from ELAS communications the Germans were also able to read some of the messages sent by British liaison officers assigned to the Greek partisans. The German Army’s codebreaking agency OKH/Inspectorate 7/VI was able to decode some of these messages in the period 1943-44 (3).

The British authorities kept in contact with partisan groups in the Balkans through liaison officers sent by the intelligence services SIS and SOE. These small teams transmitted traffic by radio to their controlling stations in Cairo, Egypt and Bari, Italy. The cryptosystems used were double transposition and the War Office Cypher, enciphered with one time pads.

Some of the encoded radio traffic of British officers in the Balkans was exploited by the Germans. They were able to read messages both through captured material and by cryptanalysis. 

The reports of KONA 4 show that some cipher material was captured in the field and messages read. For example in 1943:

Field units had to rely on captured material in order to read British agents transmissions but this was not necessarily true of the central department. The reports of Inspectorate 7/VI show that this traffic (special traffic to Cairo with indicator GESH) was first solved in June 1943 by Referats 6 and 12:

Traffic continued to be read till November 1944 but it seems this was mostly from the team assigned to the headquarters of General Mihailović and from the liaison officers in Greece. 

For example:

September ’43:

April ’44:

July ’44:

Conclusion

In the period 1941-44 the Greek population suffered under a triple occupation by Italian, German and Bulgarian forces. The collapse of the Greek State, of the economy and the falling living standards led many Greeks to take up arms against the occupiers.

This situation gave the Greek Communist Party an opportunity to build up a large partisan movement in the countryside and use it to monopolize the anti Axis resistance in Greece. With support from the British and after capturing Italian heavy weapons in 1944 the Communists were one step away from gaining power in the country.

During this period the German authorities were aware of the growing strength of the partisan movements in the Balkans but they did not have the military forces needed to permanently destroy them. Instead their forces garrisoned strategic areas and urban centers.

Both in Yugoslavia and in Greece they were able to monitor the military operations and political maneuvers of the partisan movements through signals intelligence.

In 1944 the German Army’s signal intelligence agency was able to solve a large part of the ELAS radio traffic. Their success was possible mainly due to the many mistakes made by the ELAS cipher clerks. This traffic provided valuable intelligence on the ELAS organization, personalities and planned military and political actions.

Notes:

(1). A good summary of the main issues surrounding the goals of the Communist party and EAM ELAS can be found in ‘Εμφύλια πάθη: 23+2 νέες ερωτήσεις και απαντήσεις για τον Εμφύλιο’ - Στάθης Ν. Καλύβας, Νίκος Μαραντζίδης (2016)

(2). KONA 4 - Ez Bericht 1944/II, Ez Bericht 1944/III, Ez Bericht 1944/IV (NARA - RG 457 - Entry 9032 - box 22 - ‘German deciphering reports’)

(3). The secret messages of Marshall Tito and General Mihailović

(4). Confidential Files in Room 6527 - Greece

Additional information:

1). In TICOM report I-170, p9 an example is given of the ELAS double transposition cipher. 

The sample message reads:

OMADA MERARchIWN MAKEDONIAS ch ch ch IMERA ch  STOP SAS PARAKALOYME NA ANAFERATE AMESWS EAN OI PENTE AXIWMATIKOI THS BRETTANIKHS APOSTOLHS AFIchHSAN STOP STEFANOS SARAFHS YF

My translation: ‘For Macedonian group of divisions – Day – STOP we request that you report immediately if the five officers of the British mission have arrived STOP Stefanos Sarafis’.

Stefanos Sarafis was the military commander of the ELAS forces.

2). It seems that the Greek communist military forces continued to use insecure cipher systems even in the late 1940’s. An FBI report dated August 1950 (4) says the AFSA (Armed Forces Security Agency) was working on the following Greek communist crypto systems:

These were monome-dinome substitution (enciphered with additive) and single and double transposition, similar in concept to the systems used in 1944.

It is reasonable to assume that the use of insecure ciphers by the communists was exploited by the Greek Army and US agencies during the Greek Civil War.

Acknowledgments: I have to thank Frode Weierud for translating the KONA 4 summaries and Randy Rezabek for sharing his copies. 

The compromise of the Croat Enigma K cipher machine by the German Army’s codebreakers

Signals intelligence and codebreaking played an important role in WWII. British and American codebreakers solved many important Axis crypto systems and similarly their Axis counterparts also had their own successes.

Both the Allies and the Axis powers solved not only their opponents’ communications but also those of neutral powers and in some cases the communications of their own allies.

For example the German codebreaking agencies solved Japanese and Italian diplomatic ciphers during the 1930’s and in WWII.

The Germans also solved the messages of their minor allies. One such case concerns the Enigma K (commercial version) used by the Armed Forces of the Independent State of Croatia in WWII.

The Independent State of Croatia

The Kingdom of Yugoslavia was one of the states that were created when the old Austro-Hungarian empire collapsed at the end of WWI. The country covered a large area in the Balkans but was politically unstable since it was made up of a diverse group of peoples (Serbs, Croats, Slovenes, Montenegrins). 

In April 1941 the country was quickly defeated and occupied by German forces. The collapse of the Yugoslav state led to its partition into new states, subservient to the Axis powers.

One of them was the Independent State of Croatia, ruled by the Ustaše movement and its leader Ante Pavelić.

Although the Croat State was a puppet state of Germany its communications were targeted by the German Army’s codebreakers.

The German Army High Command’s codebreaking department

During WWII the German Army made extensive use of signals intelligence and codebreaking in its operations against enemy forces. German commanders relied on signals intelligence in order to ascertain the enemy’s order of battle and track the movements of units.

The German Army’s signal intelligence agency operated a number of fixed intercept stations and also had mobile units assigned to Army Groups. These units were called KONA (Kommandeur der Nachrichtenaufklärung) - Signals Intelligence Regiment and each had an evaluation centre, a stationary intercept company, two long range signal intelligence companies and two close range signal intelligence companies.

The KONA units did not have the ability to solve complicated Allied cryptosystems. Instead they focused on exploiting low/mid level ciphers and even in this capacity they were assisted by material sent to them by the central cryptanalytic department. This was the German Army High Command’s Inspectorate 7/VI. 

Inspectorate 7/VI had separate departments for the main Allied countries, for cipher security, cipher research and for mechanical cryptanalysis (using punch card machines and more specialized equipment).

The codes of Balkan countries and of the Tito and Mihailović resistance movements (1) were worked on by Referat 6. This department also solved Croat communications in the period 1941-45 (2).

Yugoslav communications were also worked on by a small detachment under Lieutenant Wollny (Nachrichten Aufklärung Zug ‘W’) based in Belgrade and by the units of KONA 4 (Kommandeur der Nachrichtenaufklärung 4 - Signals Intelligence Regiment 4).

The Croat Enigma K cipher machine

According to German reports the Croatian forces used several cryptosystems, from Caesar cipher and simple transposition to 4 and 5-figure enciphered codes.

A more interesting system identified in Croatian radio traffic was the Enigma K cipher machine.

Since the 1920’s the Enigma cipher machine was sold to governments and companies that wanted to protect their messages from eavesdroppers.

The latest version of the commercial Enigma machine was Enigma K. In WWII this device was used by the Swiss diplomatic service and armed forces and also by the Croatian authorities.

The device worked according to the Enigma principle with a scrambler unit containing an entry plate, 3 cipher wheels and a reflector. Each of the cipher wheels had a tyre, marked either with the letters of the alphabet or with the numbers 1-26, settable in any position relative to the core wheel, which contained the wiring. The tyre had a turnover notch on its left side which affected the stepping motion of the device.

The position of the tyre relative to the core was controlled by a clip called Ringstellung (ring setting) and it was part of the cipher key, together with the position of the 3 cipher wheels.  

The commercial version was different from the version used by the German Armed Forces in that it lacked a plugboard (stecker). Thus in German reports it was called unsteckered Enigma.

The Croatian authorities first received 12 Enigma machines in July 1942 (3). More machines were purchased in 1943 and 1944. In the period November ’43 - March ‘44 Enigmas that had been used by the Condor Legion in Spain were rewired for the General Staff of the Croatian Home Defence Forces (Kroatischen Landwehr – Hrvatsko Domobranstvo) (4).

The reflector remained on the commercial wiring Ch 11 Tz 86, however the 3 cipher wheels received the new wiring Ch 11 Tz 364 a–c (5).

In total 12 new Enigma cipher machines and 29 rewired ones were prepared for Croatian use. In addition it is likely that another 44 machines were also delivered (6).

Solution of Croat Enigma K communications

Details on the solution of Croatian messages enciphered on the Enigma K are available from the postwar interrogation of Army cryptanalyst dr Buggisch and from the relevant entries in the War Diary of Inspectorate 7/VI.

Dr Buggisch, one of the top cryptanalysts of Inspectorate 7/VI, said in TICOM report I-92 ‘Final Interrogation of Wachtmeister Otto Buggisch’, p2-3

2. Solution of Croat Enigma. This was not an outstanding cryptanalytic achievement. The machine used was the K model, with three wheels and no stecker. The machines were made for the Croats by the firm of KROSKY and KRUGER, Berlin, which gave the wirings promptly to OKW/WNV in about 1941 or 1942. A single key was used throughout the entire Croat Army and area, and this consisted only of a list of 100 settings for a period of a month. As far as Buggisch knew the Ringstellung stayed always at AAA, and the wheel order at 1, 2, 3. Just to make sure, the Germans paid for one of the first keys used, and with this decoded traffic were able to establish stereotypes and solve almost 100% from the first.

The solutions were done entirely by hand with wiring charts, assuming a pet beginning (one third of all messages began with "MINORS") and assuming the left hand wheels and Umkehrwalz unmoving (only one notch per wheel as in the commercial model). The Croats also had pet indicators and so would furnish depths in case this method did not work. The setting was indicated directly by a two digit number unenciphered, so that the settings wore solved almost as fast as they came, and the traffic read currently from then on. Buggisch did not recall the contents in detail. 90% of it was uninteresting; there were some interesting messages about actions against Tito

Buggisch said the Germans had considered equipping the Croats With the military Enigma, as they did for HUNGARY, ROUMANIA, FINLAND and ITALY (and JAPAN, he thinks) in about 1942. However, they decided against this as they believed the corrupt CROATS would go right on selling the keys to British agents, while they, the GERMANS, would have to pay as well instead of solving free. (The possibility of a BRITISH solution obviously did not occur to Buggisch during this discussion of the K model.)

According to Buggisch one third of all messages began with the word ‘MINORS’. MINORS stood for ‘Ministarstvo Oruzanih Snaga’ - Ministry of Armed Forces of the Independent State of Croatia (7).

Thus this was high level traffic between the Ministry of Armed Forces and the regional military commands.

The war diary of Inspectorate 7/VI (8) confirms Buggisch’s statements and shows that in the period 1943-45 the Croatian Enigma was regularly read by the Germans.

Information from the War Diary of Inspectorate 7/VI

In June ’43 the report of Referat 13 (security of German cipher machines) said that the use of the commercial Enigma K machine had been identified in Croatian 5-letter cipher traffic and by using the wheel wirings supplied by the company Heimsoeth & Rinke together with known key documents it was possible to break into this traffic. Presumably ‘known key documents’ would have been the compromised documents that Buggisch mentioned in report I-92.

Bei einem kroatischen 5B-Verkehr wurde festgestellt, daß er mit einer handelsüblichen Enigma Modell K verschlüsselt ist. Ein Versuch mit den von der chiffriermaschinengesellschaft Heimsoeth & Rinke an Kroatien gelieferten Walzen ergab, daß tatsächlich die betreffenden Walzenschaltungen benutzt wurden. Unter Ausnutzung teilweise bekannter Schlüsselunterlagen gelang ein Einbruch und damit die Deutung der Schlüsseltechnik. Nach früher hier entwickelten Methoden wird eine laufende Entzifferung möglich sein.

In einer Besprechung am 8.6.43 wurden einige Entzifferungergebnisse über die handelsübliche Enigma mit dem Forschungsamt ausgetauscht. (Wm.Döring, Uffz. Rinow.)

In July ’43 the report of Referat 6 (Balkan countries) said that there was cooperation with Referat 13 (Wm. Buggisch) on the solution of the Croat Enigma. 23 indicators (for the initial position of the rotors) were recovered and transmitted to Lieutenant Wollny’s Nachrichten Aufklärung Zug ‘W’, together with a cipher machine for processing the accumulating material.

Von den mit Chiffriermaschine verschlüsselten kroatischen Sprüchen wurden unter Zusammenarbeit mit Referat 13 (Wm. Buggisch) 23 Kenngruppen (für Walzeneinstellung) gedeutet und mitsamt einer Chiffriermaschine fur Nachr. Aufkl.-Zug "W" zwecks Bearbeitung des dort anfallenden Spruchmaterials Herrn Oberleutnant Wollny übergeben. Die mit der Chiffriermaschine gelösten Sprüche wurden in einer umfangreichen VN-Meldung herausgegeben. (s.Schrb. Br.B.Nr. 1691/43 gKdos.)

The report of Referat 13 said that by solving the frequently used indicators it was possible to solve almost all the traffic.

Bei den kroatischen 5B-Sprüchen, die als Enigma-Sprüche (Modell K) erkannt wurden, konnten die häufig benutzten Kenngruppen erstellt werden, sodass fast der gesamte Verkehr mitgelesen werden kann.

A table contained in the Referat 6 report shows how many messages were processed during the month:

In August ’43 Referats 6 and 13 solved 16 indicator groups and transmitted them to Nachrichten Aufklärung Zug ‘W’ via teletype.

Referat 6:

Von den mit Chiffriermaschine verschlüsselten kroatischen Sprüchen wurden unter zusammenarbeit mit Referat 13 (Wm. Buggisch) 16 Einstellungsgruppen gedeutet und dem Nachr. Aufkl. Zug mit Fernschreibgspräch (G-Schreiber) am 10 und 17.8 zwecks Bearbeitung des dort anfallenden spruchmaterials mitgeteilt.

In September ’43, indicator groups continued to be solved and sent to the Wollny unit for direct exploitation. However according to the Referat 13 report the Croatian authorities changed the indicator system by having 10 new indicators valid for each day instead of the previous arrangement for 100 indicators valid for each quarter.

Nachdem die Kroaten von Vierteljährlichen Schlüsselwechsel (100 Schlüssel) zu täglichem Schlüsselwechsel (10 Schlüssel) übergegangen sind, erfordert die laufende Erstellung der schlüssel mehr Arbeit als bisher.

In October ’43, 13 indicators were sent to the Wollny unit. The report of Referat 13 says that the current solution of the indicators could be stopped. This would seem to imply that they got copies of the indicator tables, thus they didn’t need to solve them cryptanalytically.

Da die Schlüsselunterlagen zur kroatischen Enigma anderweitig besorgt werden, konnte die laufende Erstellung der schlüssel Mitte des Monats eingestellt werden.

In November ’43 the report of Referat 6 says that Croatian ciphers were solved (hand systems and cipher machine) and the results transmitted to Nachrichten Aufklärung Zug ‘W’.

Bearbeitung umfangreichen Spruchmaterials aus dem kroatischen Funkverkehr, Entzifferung einfacher Würfel und mit Chiffriermaschine verschlüsselter Sprüche. Herausgabe von 9 V.N.-meldungen aus diesem Verkehr. sämtliche hier erstellten Losungen und neuen überschlüsselungsarten wurden dem N.A.Zug "W" fernschriftlich oder schriftlich mitgeteilt.

In December ’43 there were organizational changes in Inspectorate 7/VI, with Referat 6 becoming Referat a5 and Referat 13 becoming Referat b2.

New indicators were recovered by departments a5 and b2. The report of b2 says that the solution of the Croat Enigma indicators had to be resumed because procurement was not yet possible in the new key period.

Referat b2

3. Enigma: Die erstellung der kroatischen Schlüssel wurde wieder aufgenommen, da die Beschaffung auf dem früheren Weg in der neuen Schlüsselperiode noch nicht möglich war.

Also in the second half of 1943 Referat 9, which was the Hollerith/IBM punch card section, did statistics on the Croatian Enigma traffic (Statistische Untersuchungen für kroatische Enigma für Wm. Buggisch) and on Croat language bigram and trigram statistics (Bi- und Trigrammstatistik aus kroatischen Klarsprüchen für Wm. Buggisch)

In February ’44, 18 indicator groups were solved.

The March ’44 report of Referat a5 says that the extensive Croatian Army traffic was tackled only at the forward unit Nachrichten Aufklärung.

Referat a5

Ehem. Südslawien - Freies Kroatien:

Bearbeitung des gesamten umfangreichen Heeres - Spruchmaterials ( einfache würfel, spaltencäsaren, Enigma) erfolgt nur noch bei N.A.

11 VN- Meldungen mit 208 Sprüchen

In April, May and June ’44 there seems to have been a halt on interception of this traffic. The April’ 44 report says that ‘for unknown reasons message interception has been discontinued as of 6.4’

Referat a5

Ehem. Südslawien - Freies Kroatien:

6 S- Meldungen mit 119 Sprüchen

Spruch aufnahme is mit  dem 6.4 aus unbekannten Gründen eingestellt worden, was sehr bedauerlich, da bei evtl. späterer Neubeobachtung erfahrungsgemäss die Ez. erheblichen Zeit- und Arbeitsaufwand erfordert.

Interception resumed in July ’44 with the report pointing out the negative consequences of losing touch with this traffic (‘The three-month interruption of interception makes itself felt in a disadvantageous manner’)

Referat a5

Ehem. Südslawien - Freies Kroatien:

Eingestellte Beobachtung am 1.7.44 wieder aufgenommen. Spruchanfall mässig. 48 Sprüche (einfache Würfel) entziffert, inhalt belanglos. Bearbeitung von 5Z- Sprüchen (vermutlich überschlüsselter 4Z-Code ) bisher ohne Erfolg. Die dreimonatige unterbrechnunh der Beobachtung  macht sich nachteilig bemerkbar. Angeforderte Schlusselunterlagen von Kdr 4 nicht eingegangen.

In August ’44 Referat b2 resumed work on the solution of the Enigma indicators.

Referat b2

Bei wieder aufgenommener Bearbeitung der kroat. Enigma konnten einige Schlüssel erstellt werden.

In September ’44, 7 indicators were recovered by Referat b2.

In October ’44 there was another organizational change with Referat a5 becoming Referat 3c and Referat b2 becoming Referat 1b.

During the month 5 indicators were created and results transmitted to KONA 4 (Kommandeur der Nachrichtenaufklärung 4 - Signals Intelligence Regiment 4) in the Balkans.

In November ’44 solutions increased with 33 indicators transmitted to Referat 3c.

Referat 1b

Erstellung von 33 Schlüsseln für kroatische Enigma und Weiterleitung an 3c.

In December ’44, 59 indicators were recovered.

In January ’45 Referat 3c became Referat 2c. The report of Referat 1b says that 47 keys for the Croat Enigma were solved and transmitted to Referat 2c.

In February ’45 the Ref 1b report simply says that a large number of keys for the Croatian Enigma was solved and passed on to Ref 2c.

Eine grössere Zahl von Schlüsseln für die Kroat. Enigma wurde gelöst und an Ref.2 c weitergegeben.

The final Ref 2c report from March ’45 says that 30 keys were recovered and 354 messages solved.

Referat 2c

1. Balkan- Freies Kroatien

a). Für die mit der Enigma verschlüsselten 5B-Sprüche des Kroatischen Heeres wurden 30 Schlüssel erstellt. Es wurden damit 354 Sprüche entschlüsselt.

Notes:

(1). The secret messages of Marshall Tito and General Mihailović

(2). Reports of Referat 6 – War Diary of Inspectorate 7/VI

(3). Correspondence with Frode Weierud.

(4). ‘Spanish Enigma: A History of the Enigma in Spain,’ p11

(5). ‘Spanish Enigma: A History of the Enigma in Spain,’ p11 and CroatianMachines.pdf

(6). Correspondence with Frode Weierud.

(7). Correspondence with dr Nikica Baric of the Croatian State Archives

(8). German Foreign Ministry’s Political Archive - TICOM collection - files Nr 2760-2761

Additional information:

The files of Inspectorate 7/VI, listed in TICOM report IF-272 - TAB ‘D’, include the following report on the Croatian Enigma in page 8:

Zusammengefasste Umkehrwalze. Kroatien. AA-AZ.

Walze I. II. III.

These should be the wirings for the reflector and the three wheels.

Acknowledgements: I have to thank Frode Weierud for his help in translating the relevant passages from the War Diary of Inspectorate 7/VI and for the information on the Croat Enigma orders and dr Nikica Baric for explaining the meaning of the term MINORS.