In the interwar period Czechoslovakia followed a foreign policy supportive of France and was part of the Little Entente. The country had a stable democracy and its industrial resources were large (based on the Skoda works) for such a small country. However there were two important problems affecting Czech national security. On the one hand the rise of Nazi Germany and its rearmament was a clear security threat. At the same time there were serious problems with the German and Slovak minorities that resented Czech rule.
Czechoslovakia contained a large number of minorities that were dissatisfied with the ruling Czech establishment. Especially the German minority made up roughly 23% of the population (according to the 1921 census) and a large part of it was concentrated in the border with Germany called Sudetenland. Many of the Sudeten Germans wanted for their areas to be unified with Germany and in the 1930’s Hitler’s Germany supported the demands of the Sudeten German Party. These claims were rejected by the Czech government of Edvard Beneš and as the Czech crisis threatened Europe with a new war a conference took place in Munich between the governments of Germany, Italy, Britain and France.
Without support from Britain and France the Czech government was forced to cede the Sudeten territories to Germany and also lost other disputed areas to Hungary and Poland. Even though Germany had succeeded in absorbing the Sudeten areas and in weakening Czechoslovakia that did not stop Hitler’s offensive plans and in March 1939 German troops invaded and occupied the rest of the country. From then on the country was ruled by Germany and special attention was given to its heavy industry which produced weapons for the German armed forces.During the war the Czech Government in Exile, headed by Beneš, was based in London and had regular communications with the Czech resistance. The most daring operation of the resistance was the assassination of Reinhard Heydrich, protector of Bohemia and Moravia and former head of the Reich Main Security Office. However after this episode the Germans took many security measures and were generally able to keep the resistance activities under control. In this area they took advantage of the insecure communications between the resistance and the Czech intelligence service, operating from Britain.
Referat 12 and the Czech MBM networkThe solution of Czech resistance codes is mentioned in TICOM report I-115 ‘Further Interrogation of Oberstlt METTIG of OKW/Chi on the German Wireless Security Service (Funkuberwachung)’, p8. This report was written by colonel Mettig, head of the German army’s signal intelligence agency in the period 1941-43.
According to Mettig the communications between Britain and Czechoslovakia were read by the Germans and they contained reports on the political situation and the operations of the Czech resistance.
The monthly reports show that the codes of the Czech resistance (called mbm network) were investigated in 1942 and in the period October-December they were finally solved.In October there was a meeting in Prague between the head of Referat 12, dr Vauck and Abwehr, Gestapo and Ordnungspolizei officials. Thanks to information gathered by their agents it was possible to identify some of the books used to encipher the Czech messages. One of these was ‘Svetova Revoluce: Za Valky a ve Valce 1914-1918’ by Tomáš Masaryk (founder and first President of Czechoslovakia). Some messages were solved at the Vienna Postal censor office (Ausland Brief Prüfstelle) by one of their agents.
Report of October 1942
The cooperation with Ag WNV / Fu III aJ continued as to be as active as before. On 21.10. Oblt. Vauck traveled to Prague with two men from the Department to clear and remove the deciphering difficulties of the messages on the lines 9 and 11 of the Czech mbm network. Meetings with the Abwehrstelle (Abwehr branch) Prague (Captain Dr. von Breitenberg ), Gestapo ( Kriminalrat Schulze ) and Order Police resulted in: The 12 key books indicated on the basis of earlier agent interrogations do not come into question.
The agents’ statements in these and other points do not correlate. The books were left at the Prague Abwehr branch. The from now on designated as relevant key books are: Masaryk, Svetova revoluce ; General Inger’s Letter; some magazine numbers - were not known neither at Ag WNV / Fu nor In 7/VI.Useful decryption information, which should have been in the records of the Order Police, had been sent to Vienna and there given to a V-man (agent) Emil for processing of the messages. Berlin offices have not received these documents. Instead of the V-man called back to Prague came, after one and a half day’s wait and due to a misunderstanding in Vienna, another agent.
A long distance call to V-man Emil in Vienna ABP (Ausland Brief Prüfstelle – Postal censor office) revealed that he had been able to decipher some of the messages on line 9. The system turned out to be correctly known here . The Vienna V-man is still working on breaking into the double transposition of the line 11, which is difficult work for a single individual due to the number of the necessary attempts. Information about the key books and their monthly relevant page numbers as well as the useful key documents given to Vienna, should rapidly be sent from Vienna to here via the Prague Abwehr branch.Prague will send the Masaryk book. In summary, it is clear that important and useful documents have not been sent here but to Vienna, whereby the examination and processing of the material was complicated and delayed
In November there were more meetings with officials in Prague and an agreement was reached on cooperation between Referat 12 and the Vienna Postal censor office. A notable success was the discovery of secret records in a notebook of the resistance member Josef Louzecky, a native of Neumeritz. However these were enciphered so they had to be analyzed and solved.
Report of November 1942
Cooperation with Ag WNV / Fu III aJ continuous actively. To further clarify the cipher procedures in the Czech mbm - network the Head of Unit met earlier this month in Prague with the clerk of the State Police Prague. Significant details were finalized already there and finally at a second meeting at the Ausland Brief Prüfstelle (ABP - Postal Censor Office) in Vienna around the 20th this month. Their knowledge allowed here the first successful break in line 9 of the Czech resistance movement. In a meeting chaired by the head of the Vienna ABP, lieutenant colonel von Gross, the guidelines for further cooperation in the form of a working group with the cipher specialists of censor office laid down. Again, the personal agreement proved to be conducive to the tasks of the Unit.
…………………………………………………………In the messages of line 9 of the Czech mbm network a first successful break was made. 32 messages were solved. Through the acquisition of more extensive material from the central office of the radio intercept service of the Order Police further possibilities of penetration by decoding are given. The monthly change of key books or poem keys that are never transmitted over radio certainly complicate the ongoing deciphering; but suitable compromise cases will help. Also here the collaboration with the ABP in Vienna will prove to be beneficial. A rare task lay ahead with the secret records in a notebook of the Czech Josef Louzecky, a native of Neumeritz. These are encrypted by a character Caesar. By a kind of shorthand reshuffling and further transformation of the initial characters a more complicated cipher is produced. With skillful choice of the attack points a successful break was made. The transformation in clear text will take some days to complete, but promises a lot of essential information, including addresses.
In December the messages of the period April-September 1942 were solved and also the diary of Josef Louzecky, revealing ‘a considerable number of names, addresses and important information’.
Report of December 1942
Eastern networks: The messages of line 9 of the Czech mbm network has now from April to September 1942 been broken. Unteroffz. Rossiwal has discovered important changes in the Caesar construction and furthermore the origin of the daily indicator. The processing of all the material is done essentially by him.
………………………………………..The secret records in the notebook of Czech agents Louzecky deciphered Uffz Schreier as homophonic character Caesar. The complete decryption yielded a considerable number of names, addresses and important information.
In 1943 and 1944 messages continued to be deciphered, even when the cipher was changed. The cipher systems mentioned in the reports were:1). 2-figure code plus double transposition of the digits using a book as a generator for the transposition keys.
2). 2-figure code enciphered with repeating 10-figure sequence.3). 2-digit code with columnar transposition, additionally super-enciphered.
Report of January 1943
The messages of line 9 of the Czech mbm networks are now broken by decipherment for the whole year of 1942. In the last two months more than 300 messages of the year have been deciphered, the rest will be done in the first weeks of February. A material of smaller size with no indicator groups – supposedly operational messages – has been split into the here known and practiced system: double transposition and afterwards 2-digit Caesar substitution. The deciphering will, due to the existing compromises, be possible at the earliest moment.At line 11 new messages with a four-fold over-ciphering of the basic Caesar have arrived; they will be attacked by line 11 in the course of their processing.
Report of March 1943
The main method seems to have been the 2-figure code with double transposition. This means that the letters of the alphabet would be assigned a 2-digit equivalent (A=56, B=39, C=04, etc). Then the message would be encoded using this system and the result would look like a random sequence of numbers. This sequence would be further enciphered with the double transposition system, using ‘key’s taken from a prearranged book. The indicator of the message would let the other party know which page and line of the book was chosen as a ‘key’. In theory this system was quite secure but in practice it was solved by the Germans.Overall a significant amount of Czech messages were solved in the period 1942-February 1944 (last month of available Referat 12 reports).
Jan ’43 - 300May ’43 - 366
June ’43 - 431July ’43 - 309
August ’43 - 215Sept ’43 -196
Oct ’43 - 111Nov ’43 - 134
Dec ’43 - 249Feb ’44 - 262
The STP cipher and the Slovak National Uprising
The compromise of Czechoslovak resistance radio communications is also examined in a report written by Karol Cigan, head of the cryptology section of the 2nd Department of the Czechoslovak Ministry of National Defense for the period 1949-59 (2).
The report ‘Dopady lúštenia šifrovacieho systému čs. londýnskeho MNO z rokov 1940-1945 na domáci odboj’, can be found in the archive of the Museum of the Slovak National Uprising in Banská Bystrica and in the Central Military Archive at Prague.
In the report Cigan analyzed the Czechoslovak STP cipher (letter to figure substitution followed by transposition and then additive encipherment, with repeating additive sequence) and found it insecure. In addition he proved the compromise of Czechoslovak ciphers by examining reports from the office of the high ranking SS official Karl Hermann Frank.
A report from November 1944 had a summary of Funkwabwehr (Radio Defense) operations and it said that during the previous month 8 radio links, whose cipher procedures could be solved, were kept under observation. Of special interest was traffic between the Protectorate and London regarding the preparations for the uprising.
In the month of October ’44 a total of 488 messages were solved and 8 cipher keys derived for the STP cipher.
In pages 37-41 Cigan directly compared the Funkawbehr decodes with some of the Czechoslovak telegrams found in the country’s national archives. For example messages exchanged between the Minister of National Defense General Ingr and Ján Golian and Jaroslav Krátký in the Protectorate and with Heliodor Píka in Moscow.
The author’s conclusion was that the use of insecure ciphers during wartime played an important role in undermining the operations of the Czechoslovak resistance movement and these events should be acknowledged by the country’s historians.
One of the systems solved by the Swedish codebreakers was the double transposition code used by the Czech intelligence service (3). In the period 1939-42 the former Czech embassy counselor Vladimír Vaněk was living in Sweden and he collected information on political and military development through his friends and acquaintances in Stockholm. Vaněk had regular talks with important individuals such as government ministers and even the private secretary of Prime Minister Per Albin Hansson.This information was then sent in code to the Czech government in Exile, based in London. His messages had the indicator CXG and were actually transmitted by the British embassy in Stockholm. The Swedes had been intercepting this traffic since 1940 and after an extensive cryptanalytic attack were able to ‘break’ the system and read most of the traffic of the period August 1941-March 1942.
In March 1942 the house of Vladimír Vaněk was raided and the Swedes searched for incriminating evidence, including a ‘big red book’ that he had mentioned in one of his decoded messages. They did find it and it was indeed red but not really big. This was the book used to create the transposition keys. It’s name? Svetova Revoluce…
Notes:(1). War diary of Inspectorate 7/VI
(2). Report ‘Dopady lúštenia šifrovacieho systému čs. londýnskeho MNO z rokov 1940-1945 na domáci odboj’ by Karol Cigáň (Central military archive Prague, Fond Karol Cigáň No. 207/89), Application and Misapplication of the Czechoslovak STP Cipher During WWII and ‘STP cipher of the Czechoslovak in-exile Ministry of Defence in London during WWII’ by Štefan Porubský.
(3). ‘Codebreakers: Arne Beurling and the Swedish Crypto Program During World War II’, chapter ‘The double transposition’
Acknowledgements: I have to thank Frode Weierud for translating the Referat 12 reports.
3). The reports Dopady lúštenia šifrovacieho systému čs. londýnskeho MNO z rokov 1940-1945 na domáci odboj’ (found in the Central military archive Prague) and ‘STP cipher of the Czechoslovak in-exile Ministry of Defence in London during WWII’ by Štefan Porubský.
Information on Czechoslovak ciphers is available from the following sources:
1) .The books Odhalena tajemstvi šifrovacich kličů minulosti, Gentlemani (ne)čtou cizi dopisy and Válka šifer. Výhry a prohry československé vojenské rozvědky (1939-1945) by Jiri Janecek.
2). The following ‘Crypto World’ articles by Jozef Kollár:
Cipher ‘TTS’ (double transposition of the text followed by letter to figure substitution)
Cipher ’Rimska dva’ (letter to figure substitution followed by double transposition of the digits)
Cipher ‘Rimska osem’ (homophonic letter to figure substitution followed by encipherment with repeating 10-figure additive sequence)
Cipher ‘Rimska devat’ (letter to figure substitution followed by additive encipherment, repeating additive created from a passphrase)
Cipher ‘Rimska desat’ (letter to figure substitution followed by transposition then additive encipherment, repeating additive created from a passphrase, passphrase is also used to limit the cells of the transposition table)
Cipher ‘Rimska trinast’ (transposition of the text followed by polyalphabetic substitution)
Cipher ‘Eva’ (transposition of the text using a pyramid shaped transposition table)
Cipher ‘Marta’ (letter to figure substitution followed by additive encipherment, additive created via passphrase autoclave procedure)
Cipher ‘Ruzena’ (letter to figure substitution followed by additive encipherment, additive created via passphrase procedure)
Cipher ‘Utility’ (letter to figure substitution followed by transposition)
Cipher ‘Palacky’ (letter to figure substitution followed by additive encipherment, additive created via passphrase procedure, cipher digits multiplied by a constant)
I read in a swedish book that when one of the war time cryptographers was interviewed he suddenly realized that CXG must have meant Czech Exile Government. It did not strike him at the time though. If the indicator in fact /did/ mean this was not known by him.ReplyDelete
That's from Bengt Beckman's book ‘Codebreakers: Arne Beurling and the Swedish Crypto Program During World War II’Delete
Very likely so. I read it years ago and that little tidbit stuck.Delete
Great read but I'm having trouble understanding the Palacky Cipher. I may be missing something in the translation but as I understand it, the ciphertext is multiplied by a constant (3 in the example) modulo 10 and so would be irreversible.ReplyDelete