Monday, April 18, 2016

The ciphers of Czechoslovakia’s government in exile

At the end of the First World War the multiethnic Austro-Hungarian Empire collapsed and out of its ruins emerged several new countries. One of these was Czechoslovakia, containing the Czech areas of Bohemia and Moravia together with Slovakia and Carpathian Ruthenia in the east.

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 Czechoslovak Government in Exile, headed by Beneš, was based in London and had regular communications with the Czech resistance and with its diplomatic missions and intelligence service stations abroad. In order to protect these communications several cryptosystems were used by the Czech crypto department.

Information on these systems is available from books and articles written recently:

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 have descriptions of the ciphers and the author’s conclusion was that the security afforded by these systems was limited.

2). A series of articles written for ‘Crypto World’ by Jozef Kollár describe each cipher system, explain how to encipher and decipher and also evaluate their security. The articles are:

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)

Compromise of Czech ciphers

The Czech resistance movement and the Czech intelligence service caused serious problems for the German authorities with their most audacious operation being 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. Keeping the Czech areas pacified was particularly important since Czechoslovakia had a developed heavy industry sector which produced weapons for the German armed forces.

In their counterintelligence operations the Germans benefitted from having the ability to read a substantial amount of the traffic exchanged between the Czech IS in Britain and the Czech resistance in the occupied territories. This case has been covered in detail in Svetova Revoluce and the codes of the Czechoslovak resistance.

Report on the compromise of the communications of the government in exile

After the end of WWII it seems that the Czechoslovak authorities learned from POW interrogations about the compromise of their ciphers. Karol Cigáň, who worked in the Defense Ministry’s cipher department, summarized some of this information in a report written in 1989.

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 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 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. 

Acknowledgments: I have to thank Jozef Krajcovic for his help in locating the report ‘Dopady lúštenia šifrovacieho systému čs. londýnskeho MNO z rokov 1940-1945 na domáci odboj’ and Štefan Porubský for informing me of the articles from Crypto World. 

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