https://orcid.org/0000-0002-9685-6051
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Abstract
Josef Růžek was one of the best cryptography and cryptanalysis specialists in Czechoslovakia. In addition to his various achievements in cryptanalysis, he was involved in building the encryption service and training new experts in cryptanalysis in Czechoslovakia. We present detailed information on the origin of cryptanalysis in Czechoslovakia based on documents from Czech and Slovak archives. We mainly focus on the written courses of cryptanalysis organized by Růžek and on the first Czechoslovak manual of cryptanalysis.
Acknowledgements
I would like to thank Tamás Fördős, Ingo Niebel, Viliam Hromada, and Pavol Zajac for their help.
Disclosure statement
No potential conflict of interest was reported by the authors.
Notes
1 Later also the president.
2 It was also called “hlavní štáb” which directly translates to Main Staff.
3 The 2nd department of the General Staff was established on 10 July 1919 (MNO Citation1919).
4 In the document, this is formulated as “uncovering enemy ciphers”.
5 One of the military tasks of intelligence services during peacetime is to collect encrypted radiotelegraphic messages, probably for further cryptanalysis.
6 The first draft was issued in 1936 and the commenting phase was due on December 15th, 1936 (VHA Citation1936).
7 Additional directives from 1932-1938 are available, which are related to the intelligence service, but either they do not contain any significant information for this publication (e.g. G-VII-9, G-VII-10), or only the proposal has been preserved and it was probably not officially issued (G-VII-4).
8 Růžek stated in (Růžek Citation1950a) that he created the first cryptographic directive issued in Czechoslovakia with the same name “šifrování” in 1924/1925. However, he mentions a different number, G-1 (which officially belongs to a different directive, see (MNO Citation1922)). We are unable to confirm whether this is connected to directive G-VII-8 or not. There are no documents available about the directive from 1924/1925. Moreover, in documents about the directive’s commenting procedure (VUA Citation1937) it is clearly stated that it is a new directive.
9 The G-VII-8 was also adopted as the main cryptographic directive in Slovakia during WW2. It was extended in 1943 with directives from Germany (without changing the name of the document). At this time, Slovakia also adapted some German ciphers, including the Enigma, NS42, and TS42a (Antal, Zajac, and Grošek Citation2019).
10 The release was originally scheduled for the year 1937 (MNO Citation1936). The commenting procedure took place from June to August 1937 (VUA Citation1937). J. Růžek was responsible for incorporating the comments (MNO Citation1936).
11 In (ABS Citation1949) it is stated that he started doing cryptanalysis in the Austrian army. Based on (ABS Citation1965), Růžek was a disciple of a well-known Austrian cryptologist Andreas Figl.
12 First at the headquarters of the Czechoslovak army, later at the 2nd dep. of the General Staff of the Ministry of National Defence.
13 Based on (Růžek Citation1950a), he worked in the cipher section from 1922.
14 He supported several resistance groups, supplying them with ciphers (VUA Citation1910–1949; ABS Citation1946–1947, 1957) (e.g. for communication with military attaches in Paris, London, and Warsaw). He took part in the uprising on 5 May 1945 in Prague (VUA Citation1910–1949).
15 Růžek also showed the Czechoslovak pneumatic cipher machine to Fenner (NARA Citation1946), but he claimed that the machine was only in an experimental phase and had never been used. However, the (pneumatic) Štolba cipher machine was tested in the army from 1937 and used from 1938 (Antal and Zajac Citation2021).
16 Ordered by František Hájek (Head of the 2nd dep. 1935-1938) and František Moravec (Head of the 2nd dep. 1939) (VUA Citation1939a; ABS Citation1957, Citation1949).
17 It was possible to solve the double transposition (Růžek Citation1950a) because of the high traffic, and the fact that the same key was used by almost all headquarters and units, so there was a high probability of obtaining several messages of the same length. In July 1937, French Captain Dufilhol visited the Czechoslovak cipher section where he witnessed such a cryptanalytic success, based on the interception of 5 telegrams from the same day of the same length. In his report (PAAA Citation1937), he also highlighted the benefits of the Czechoslovak eavesdropping network. The solving process used was also included (Růžek Citation1950a) in chapter VI. of his manual of cryptanalysis, see Section 5. Moreover, Růžek also demonstrated (Růžek Citation1950a) the whole process to the Soviet General Staff in Moscow during his business trip in 1936.
18 Růžek (Citation1950) describes it as a grid cipher.
19 After the Enigma was commercially available, Růžek obtained and analyzed the Enigma cipher machine (marked as “Handelsenigma” in the document) and he was convinced that the machine did not meet the needs of the army (Růžek Citation1950a). Despite this fact, twelve Enigma machines were bought. To prove his claims, he requested several ciphertexts that he was able to solve within five hours. He also claimed that in some cases it is possible to solve messages encrypted with a newer version of Enigma when enough messages, encrypted with the same key, are available.
20 Before WW2 Czechoslovakia exchanged (Růžek Citation1950a) the eavesdropped encrypted communication with France, Poland, and from 1936 also with the Soviet General Staff, which allowed them to have at their disposal the whole German communication. There was also cooperation with Hungary and Austria.
21 Before his assignment to the encryption service, Růžek dealt with cryptanalysis privately (Růžek Citation1950a).
22 He was retired in 1948, however, there are also available newer documents he wrote for the army.
23 There were at least two supplemental lectures added to the course (VHA Citation1926–1936).
24 Based on Růžek (Citation1950a), around 150 participants started the course in the first year, and in the following years around 100 new participants registered yearly (VUA Citation1936).
25 This was necessary because the course was undertaken in the participants’ spare time.
26 We don’t know the exact date of the interception (the report is from 1931). The Czechoslovak document is dated 1927 in (PAAA Citation1931), and it is stated, that the translation took more than a year.
27 Without using the word steganography.
28 Cyclic use of a passphrase, as in the Vigenère cipher; however, each time only a (different length) substring of the main passphrase is used.
29 As an example, it is mentioned that a cryptogram encrypted with Enigma was solved in one of the solving competitions.
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Eugen Antal
Eugen Antal is an assistant professor at the Slovak University of Technology in Bratislava. He specializes in modern cryptanalysis of classical ciphers. His interest in classical ciphers is motivated by the famous Zodiac killer's Z340 cipher. Currently, he is investigating historical ciphers from the middle-European countries and leads the HCPortal (https://www.hcportal.eu/) project.