Monday, October 30, 2017

WWII documentary

Interesting newfound footage from WWII. Hitler’s mental and physical deterioration can be clearly seen in this documentary.

Friday, October 27, 2017

The reconstructed Slidex card

At Crypto museum I saw that they’ve uploaded some Slidex cards from 1944. I had a quick look to see if I could locate the one solved by the German codebreakers and found in the report E-Bericht FNASt 9 (US National archives - RG 457 - Entry 9032 - box 22 ‘German deciphering reports’).

I didn’t expect to find anything so imagine my surprise when I saw that the Air Support Signals Unit card No. 1 (from 1944) had the same code values:

I’ve added this card in The Slidex code.

Tuesday, October 24, 2017

Signals intelligence and codebreaking operations during the Greek-Italian War of 1940-41

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.

What role did signals intelligence and codebreaking play during that short conflict? Let’s have a look at the limited information available:

The Italian effort

Italy had two codebreaking departments, one under Army and the other under Navy control.

The Italian army’s intelligence agency SIM (Servizio Informazioni Militari) had a cryptanalytic department that attacked foreign crypto-systems. This section was headed by General Vittorio Gamba and was located in Rome. Personnel strength was roughly 50 people (half cryptanalysts-half linguists and clerks).

The naval intelligence agency SIS (Servizio informazioni Speciali della Royal Marina) was divided into 4 branches. Branch B (Beta) was tasked with signals intelligence. It was subdivided into cryptanalysis, interception and direction finding, security and clandestine radio intercepts. The cryptanalytic department was located in Rome and headed by Commander Mario De Monte.

It is not clear if the Italians had success with Greek Army or Air force codes and ciphers. However in the Archivio dell' Ufficio Storico della Marina Militare there are decoded Greek Navy messages.

Regarding the Greek Air force communications, it seems that the cipher system used was simple transposition (1). Considering the limited security of this system it is reasonable to assume that it was solved by the Italian codebreakers.

The Greek effort

At this time there is almost no information available on the Greek Army’s cryptologic and cryptanalytic effort during WWII. A report from 1938 (2) mentions the Greek Army codebooks: small unit code 1937, large unit code 1937, small unit code 1938, mobilization code 1937, cryptographic lexicon 1935.

Regarding cryptanalysis it seems that the Greek Army Signal Corps may have been able to exploit Italian communications (3). According to an article on Greek military intelligence this information comes from British liaison signal officers:

In addition, according to British liaison signals officers, Greek Signals Corps managed to decipher some Italian traffic during the November/December battles in Albania. On 6 December, a British lieutenant-colonel informed his superiors: “Herewith a batch of Italian traffic intercepted by the Greek General Staff. Also, one copy of cipher ‘O.M.’ for internal use of the Italian Army in Albania.” On 8 December, the reply confirmed Greek success: “Many thanks to Greeks for citrario O.M. Tell them I do not remember having seen it but I am very grateful for it and for any further documents of this nature which may be of assistance in reading Italian codes in Albania which I am afraid are not readable.” We could imagine that Greek Signals Corps may have deciphered key traffic during October, prior to the invasion. Unfortunately, at the Army History Service no files of Greek signals operations can be found. Perhaps some material might be held at the Military Archives Service but we must bear in mind that the 1941 German invasion and the 1941-1944 occupation caused the destruction of many files of sensitive army archives. As to Metaxas, he did not make any reference to signals intelligence in his diary’.

The German effort

The German Army’s signal intelligence agency solved Greek Army and Air force ciphers. According to the TICOM report I-170 in spring 1941 Greek AF single transposition messages were solved and translated (4):

My first employment was on the breaking and translating of Greek Air Force messages in Spring 1941. The unit was in BUCHAREST at that time and later it was at BANJA KOSTENIC in Bulgaria. C.O. was Hptm. SCHMIDT, head of the cryptography and translation department from then until Autumn 1944 was Prof. Alfred KNESCHKE, a Professor of Mathematics from Saxony.

The Greek Air Force messages were a matter of simple boxes, the text being sent in T/L groups. The indicator took the form of 3 letters which were always in a given position, the first three T/L groups and had to be knocked out before entering the cipher text in the clear box. This was broken by writing out the cipher text in vertical strips of varying depth and sliding them against each other until a few Greek syllables appeared above one another. After the initial break it became clear that a large part of the messages began with the words ‘parakalw', 'anaferw’ and ‘apesteilamen’ and that the width of the box was as a rule between 15 and 22 columns. On the basis of the above, initial words, all messages were tried out on the normal number of columns and nearly everything was read. I had less to do with the actual evaluation, firstly because the two departments were kept separate and secondly because we were kept fully occupied with our own job. In any case the content of the messages was usually of insignificant strategic value, although the continuous check on officer personalities, deliveries of stores and knowledge of airfields combined with D/F bearings indirectly contributed to considerable tactical results'.

Regarding Greek Army ciphers there is some information available from the postwar interrogations of Army cryptanalyst dr Buggisch. According to TICOM report I-58, in early 1941 he investigated a Greek codebook enciphered with a 35 figure repeating additive sequence (5). Progress was made in the solution of the cipher but the campaign ended just as the system was starting to be exploited operationally:

c. Greek - In early 1941, B. solved a 5-letter code with a 7-cyclic recipherment (period of 35). Just getting to operational speed when the campaign ended.

German exploitation of Italian communications

It seems that the codebreakers of the German Army did not only monitor the communications of their enemies but also solved the codes and ciphers of their Italian allies.

The War Diary of Inspectorate 7/VI shows that Italian codes and ciphers were worked on by Referat 4 (6). According to the reports of Referat 4 for early 1941, 5-figure and 3-figure codes were worked on:

The 3-figure Army code was successfully solved and read. A 5-figure Air Force code was also worked on and the encipherment solved. A 5-figure enciphered code used by the higher command in Albania was worked on and code groups recovered.

The reports say that emphasis was put on the analysis of the systems used by the higher echelons of command.

Some interesting statements regarding Italian radio communications are made in ‘War Secrets in the Ether’ - vol 3, p25 written by Wilhelm Flicke (he was in charge of the OKW/Chi’s Lauf intercept station):

‘Mussolini had decided on war in the Balkans. Von Papen's warnings made Hitler averse to any immediate action there, but he was only able to restrain Mussolini to the extent of limiting Italy to war with Greece. In less than two months the Italians, who had the advantage in everything save morale, were badly beaten. The political leaders were terribly surprised and the Chief of General Staff, Marshal Badoglio, and numerous other high officers were relieved of their duties. This did not help matters.

One of the most decisive factors during those weeks was the manner in which the Italians employed radio. The set-up was the same as that used in maneuvers of previous years. They employed open circular traffic; that is, they used one uniform frequency for a group of stations belonging to the same unit (e.g., the stations of three infantry regiments of a division for traffic with one another and with the divisional station) and each station used only one call sign for all its traffic. The call sign was supposed to change daily but was often used for several days; not infrequently a change in call sign was followed by errors which betrayed the change. Traffic was so heavy that the enemy always had a chance to take bearings and fix locations. Frequently messages were sent in clear. Several units of the Italian Eleventh Army distinguished themselves in this respect. Moreover, the Greeks had obtained at least two Italian army cryptographic systems, how I do not know, but it is certain that in the very first days of the campaign they could decipher a large part of the Italian messages. This enabled them to learn promptly most of the dispositions of the Italian command and to take appropriate action. The superiority thus gained was utilized cleverly and a series of military actions took place which heretofore would never have been deemed possible’.


(2). German Foreign Ministry’s Political archive - TICOM collection - file Nr. 3.676 - Griechenland 1940 - Korresp. betr. Neue milit. Schlüssel u. Vernichtung alter.

(3). Journal of Intelligence History: ‘Greek Military Intelligence and the Italian Threat, 1934–1940

(6). Kriegstagebuch Inspectorate 7/VI - German Foreign Ministry’s Political Archive - TICOM collection – files Nr 2.755-2.757

Acknowledgments: I have to thank Enrico Cernuschi for sharing the messages from the Archivio dell' Ufficio Storico della Marina Militare.

Monday, October 23, 2017


In Decoding Prime Minister Chamberlain’s messages I’ve added the following:

A clue regarding the cipher system used is available from the TICOM report DF-241 ‘The Forschungsamt - Part IV’, p40

Of the numerous examples which might be adduced, the following may serve as an example: The additive number used by Great Britain, which ran to 40,000 elements and served for the encipherment of the 5-digit code and was replaced at definite intervals of time, offered as a rule adequate assurance of security. But if in periods of greatly increased diplomatic activity with telegraphic traffic many times the usual volume the additive is not replaced correspondingly sooner, especially since increased security is desirable in such periods, then this is a sign of deficient control’.

Thus it is possible that the German codebreakers were able to solve the British Foreign Office cipher in the 1930’s.

The official history ‘British Intelligence in the Second World War’ - vol2, p642 says that:


1. Main Cypher Books

Despite an extensive attack in 1938 and 1939, the Germans failed to break the long subtractor system used to re-cypher the Foreign Office's basic cypher books. Against similar tables that were in force from November 1940 to January 1941 they had some limited success, but not enough to enable them to reconstruct the book before both the basic book and the tables were again changed. There is no evidence of later success, and according to German testimony after the war the main Foreign Office systems were never broken’.

However in the notes it also says:

The discovery after the war in the archives of the German Ministry of Foreign Affairs of  a 90-page volume of British diplomatic signals for the immediately pre-war period led to a  Foreign Office enquiry in 1968. This established that a number of the signals had been dispatched en clair. It also noted that there was reliable evidence that the Italians had obtained temporary possession of the cyphers of the Rome Embassy in 1935, and had photographed them, and that they had had fairly regular access to the cyphers at the Mission to the Holy See during the war, so that they might have read all telegrams to Rome up to the outbreak of war and telegrams to and from the Mission to the Holy See from the outbreak of war to the autumn of 1943. After the war the cryptanalysts of the German Foreign Ministry asserted that they obtained no information about British cyphers from the Italians’.

The British statements may have been accurate about the work of the decryption department of the German Foreign Ministry but they do not mention the Forschungsamt effort…

Sunday, October 8, 2017

2017 Cryptologic History Symposium

The NSA’s Center for Cryptologic History and the National Cryptologic Museum Foundation are co-sponsoring the 2017 Cryptologic History Symposium:

19 - 20 October, 2017, Johns Hopkins Applied Physics Laboratory Kossiakoff Center, Laurel, Maryland

The theme for the 2017 Symposium is "Milestones, Memories, and Momentum." There are many milestones to mark in 2017: the 160th anniversary of the first attempt to span the Atlantic with a telegraph cable, 100 years since both the entry of the United States into World War I and the Russian October Revolution, and 75 years after the World War II battles of Coral Sea and Midway. The Symposium will take place just a few months before the 50th anniversary of the Tet Offensive in Vietnam, and during the 25th year after the fall of the Soviet Union and the end of the Cold War. These milestone events and advances in cryptology, as well as how we remember their significance, provide momentum to create the systems of today and the future.

Saturday, October 7, 2017

The Communist agents cipher solved by the Forschungsamt

In the recently released TICOM report DF-240 ‘Characteristics, Analysis and security of cryptographic systems’ there is a short description of a cryptosystem used by communist agents:

It is interesting that the names mentioned in the example are Harri Meier, Theodor Felder, Albert Schwarz, Max Hamburger and Karl Gutmann. 

Wednesday, October 4, 2017


1). In Soviet cipher teleprinters of WWII, I’ve added the following:

More details about the Forschungsamt solution of the Soviet cipher teleprinter are given by Bruno Kröger in TICOM reports DF-240 and DF-241. Kröger was the FA’s cipher machine expert and during the war he solved not only the Soviet machine but also the Swiss diplomatic Enigma K.

The Soviet cipher teleprinter was used on 2-channel networks and the FA’s Technical Division was able to build equipment that automatically intercepted and printed this radio traffic. The cipher text was then examined by Kröger’s department and it was discovered that during transmission pauses the Russian letter П was enciphered seven times in succession. Messages interrupted by transmission pauses were examined and their first and last seven characters analyzed in order to uncover the operating principles of the device.

Through this cryptanalytic procedure it was possible to find out that the machine had 6 wheels that stepped regularly, then their pin arrangement was identified and with the daily key recovered all the day’s traffic could be solved.

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.

From TICOM DF-240 ‘Characteristics, Analysis and security of cryptographic systems’ - Parts III and IV, p37-39

Both texts indicated the pauses in transmission by - - - - - etc.  The cipher tape has the peculiarity that in passing from the preliminary call-up to the transmission pause, the Russian letter Π, represented in the radio alphabet by + + + + +, occurs seven times.
Now since it was natural to assume that in this transition to and from cipher texts the same letter Π= + + + + + likewise appeared seven times in each case but vas no longer recognizable due to the encipherment the first and last seven cipher values of all cipher texts interrupted by transmission pauses were subjected to special study. Since the machine, once the daily key had been set up, was used very frequently during the course of the day for sending cipher text with numerous pauses in transmission without any new daily key being set up, rather numerous fragments of a length of seven letters were available at known intervals of greater or lesser lengths.
From this it could be concluded that the first seven and the last seven letters of each secret text came from enciphering the letter Π= + + + + + seven times and hence these fragments of cipher text represented pure key text. The following study of these fragments of pure key text led to a recognition of the fact that the first impulses show the same repeated picture in the chain of plus and minus impulses at an interval of 37, the second impulses at an interval of 39, the third impulses at an interval of 41, the fourth and fifth at an interval of 43 and 45 respectively (the intervals may have been 35, 37, 39, 41, 43). This showed the length of the five cipher wheels and their cam pattern according to the day’s setting. Each cam crest caused the inversion of the plain impulse into its opposite while a cam trough left a plain impulse unchanged. The wheels regularly moved one step after each cipher letter.

With this the decipherment of the cipher text had been accomplished. The reconstruction of the cam pattern of the wheels, which was set up new each day, was easily accomplished.

From TICOM DF-241 ‘The Forschungsamt’- Part I, p25

18. The Russian radio [2-channel] cipher machine with a channel for plain text and a channel for cipher text could be studied after the Technical Division had constructed a receiving device which at the same time removed the scrambling. The five elements of the radio alphabet [bands] ware enciphered singly through five wheels which move evenly. The wheels could be set up new each day corresponding to the daily key; but the period was constant and invariable. It was possible to solve this completely.

From TICOM DF-241 ‘The Forschungsamt’- Part IV, p38

It need only be mentioned here that the 2-channel cipher machine was withdrawn from use a few days after the Forschungsamt succeeded in solving it. When the machine was put into use again some weeks later, the cipher device of the cipher channel had been so altered that solution by the previous method was no longer possible since, when switching the machine from procedure traffic to cipher text and between a pause in transmission and cipher text, the switching became effective at once and the idling period of 7 elements had dropped out. That the same machine was involved was proven only by the receiver device which still broke up the scrambled text into a clear and a cipher text in the same manner as before. Because OKH had great interest in this traffic and its own receivers did not work perfectly, and because further detailed work at this time (Autumn 1943) in the Forschungsamt was not possible, OKH received all new traffic on this machine for processing. 

2). In Compromise of Soviet codes in WWII, I’ve added information from various reports including TICOM sources and FMS P-038 ‘German radio intelligence’.

Sunday, October 1, 2017

The compromise of the Swiss diplomatic Enigma K cipher machine in WWII

In the course of WWII the Allied and Axis codebreakers attacked not only the communications of their enemies but also those of the neutral powers, such as Switzerland, Spain, Portugal, Turkey, Ireland, the Vatican State and others (1).
Switzerland was a traditionally neutral country but during the war it had close economic relations with Germany and it also acted as an intermediary in negotiations between the warring nations. Important international organizations like the Red Cross and the Bank of International Settlements were based in Switzerland.

Naturally both the Allies and the Germans were interested in the communications of the Swiss government.

Swiss diplomatic codes and ciphers

The Swiss Foreign Ministry used several cryptologic systems for securing its radio messages. According to US reports (2) several codebooks were used, both enciphered and unenciphered. These systems were of low cryptographic complexity but had an interesting characteristic in that the same codebooks were available in three languages.
French, German and Italian were the recognized official languages of Switzerland. The codebooks of the Swiss foreign ministry had versions in French, German and English.
Apart from codebooks the Swiss also used a number of commercial Enigma cipher machines at their most important embassies.

The Swiss 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.

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.

In 1938 the Swiss government purchased 14 Enigma D cipher machines, together with radio equipment. The next order was in 1939 for another 65 machines and in 1940 they received 186 Enigma K machines in two batches in May and July ’40. The Enigma cipher machines were used by the Swiss Army, Air Force and the Foreign Ministry (3).