The Bletchley Park Codebreakers (6 page)
Read The Bletchley Park Codebreakers Online
Authors: Michael Smith
Tiltman agreed a similar deal to that with Estonia, promising to provide radio equipment in return for the traffic. Unfortunately, there were immediate complications. No sooner had he returned to England than the Russo-Finnish War came to an end. Nevertheless, the Finns insisted that they were still determined to expand their Sigint operations against the Russians. There was then difficulty persuading Stewart Menzies, who had succeeded Sinclair as Chief of MI6, to pay for the Finnish equipment. Even once he had agreed, some of the wireless receivers went missing. But eventually the arrangement began to work and the Finns provided an increased flow of Russian military and KGB traffic as well as five captured codebooks: three Russian Army codebooks – two of which had already been partially worked
out by the Russian section – and two Soviet Navy codebooks. These were the KKF2 code used by the Black Sea Fleet and the KKF3 code used in the Baltic, which the British had broken a few months earlier but had not totally reconstructed.
This provided fresh impetus to the work against the Russian Navy. Russian armed forces traffic now became the subject of a major effort by GC&CS and its outstations. Radio receivers were installed in the British Legation in Stockholm. Scarborough joined Flowerdown in monitoring Russian Navy frequencies. Vlasto was sent out to bolster the Russian section at Sarafand which, along with India, weighed in with a full range of interception, traffic analysis and codebreaking, sending high-grade cipher back to England via the diplomatic bag. The RAF set up an experimental intercept site in Baghdad to target Russian army and air circuits in the Caucasus. It also monitored Russian Navy intercepts from Cairo. The Royal Navy intercept sites at Dingli in Malta, Alexandria in northern Egypt, and Ismailia on the Suez Canal took Russian Navy material and fixed locations of the transmitters using direction finding. The Far East Combined Bureau (FECB), the main British Sigint outpost in the Far East, began taking Russian traffic from the Vladivostok area and kept watch on Baltic Fleet frequencies. It even asked the Australian and New Zealand Navy intercept organizations to provide any Russian naval material they could. At GC&CS itself, French naval code-breakers, who had been transferred to Britain, began working on high-grade Baltic and Black Sea Fleet ciphers.
The flow of material from Estonia dried up in June 1940 when Russia occupied the Baltic States. But the fall of France brought willing replacements in the form of Polish wireless operators and codebreakers who, having escaped Poland to work with Gustave Bertrand, had now been forced to flee the German
Blitzkrieg
for a second time. Based at Stanmore in west London, they found they were able to monitor Russian material from the Ukraine and were co-opted by Denniston to provide more material for the Russian section.
The increased effort brought yet another break, this time at Sarafand where the KKF4 Black Sea Fleet super-enciphered code was broken in November 1940. A few weeks later, the British and Americans exchanged Sigint material primarily relating to the Axis countries. The exchange took place at Bletchley Park in February 1941 and as part of their contribution, the British handed over four
Russian codebooks: the OKF high-grade Baltic Fleet super-enciphered code broken at Wavendon and Bletchley; the EPRON codebook used by the Russian Navy Salvage Corps, which had also been worked out by GC&CS; the KKF4 Black Sea Fleet codebook broken at Sarafand; and the KKF3 Black Sea Fleet codebook provided by the Finns.
The British operation against the Russian armed forces traffic was subsequently disrupted by a major change in codes and ciphers. But Denniston told Menzies that there was no doubt that it had ‘benefited largely by the increased interception from the Poles and that our Finnish liaison is becoming really attractive. This liaison, owing to recent changes in all Russian codes, is of first importance.’ By the beginning of June, there was serious concern that the increasing collaboration between the Finnish and German General Staffs might compromise the arrangement with Finland, leading the Germans to question how vulnerable their own ciphers were. The Poles were asked to reinforce their Stanmore operation and Tiltman even sought the advice of the MI6 Head of Station in Helsinki as to whether the Finns could be trusted to keep the secret. However this debate was overtaken by events, in the shape of Operation Barbarossa – the German invasion of Russia – which began on 22 June.
According to the official history of intelligence, all intelligence operations against the Soviet Union now came to an abrupt halt on Winston Churchill’s orders. The reality was nowhere near as clear-cut. Indeed, initially, coverage was increased. There was a long drawn-out debate over whether or not to drop Soviet traffic. The codebreakers in India were only too happy to dispose of their Russian Air Force and KGB tasks which had produced ‘nothing of intelligence value’. But there were concerns that the lack of continuity would hamper attempts to break the Russian codes and ciphers in the future. As a result, it was not until December 1941 that the Russian section was closed down. Even then the Poles were told to continue intercepting traffic and trying to break it, while the British kept two sets monitoring known Russian frequencies at the Scarborough Royal Navy site and the RAF station in Cheadle.
Within weeks, the Metropolitan Police intercept site at Denmark Hill and the Radio Security Service, an organization set up to monitor clandestine radio stations which now came under the aegis of MI6, had begun to pick up messages between Moscow and its agents in Europe. Despite the Churchill edict, MI5 had continued to keep a watch on
the Russians and their links to the CPGB. But it was unaware of the ‘bundles of Russian traffic’ that had been intercepted until February 1943 when it discovered through its own sources within the party that Jean Jefferson, a party member, had been asked to resign in order to take an ‘illegal’ post operating the radio link to Moscow. Sir David Petrie, the Director-General of MI5, had a fraught discussion with Menzies at which it was agreed that Soviet espionage links should be monitored. This was subsequently refined to interception and decryption of the links between Moscow and communist parties across Europe. A small Russian team was secretly set up at a GC&CS outpost overlooking London’s Park Lane to break the cipher. The keys were taken from an English edition of Shakespeare’s plays, in order to avoid the risk of the operator being caught with a codebook. By the late summer of 1943, less than two years after they had closed their Russian section, ostensibly for the duration of the war, the British code-breakers were again reading Soviet traffic. The end of the Second World War was almost two years away, but the preparations for the second Cold War had already begun.
Although Bolshevik codes and ciphers had been the main target of the interwar years, by the time the codebreakers moved to Bletchley Park in late August 1939, these had been replaced by the attempts to break Enigma. It has been suggested that it was not until shortly before the war that the GC&CS codebreakers began to make any effort to break an Enigma machine. Although it is certainly true that Enigma had not enjoyed the highest priority during the interwar years, it was far from ignored. As the late Hugh Foss, who joined GC&CS in 1924, explains in the following chapter, he first looked into the possibility of breaking the machine in 1927, paradoxically with a view to seeing whether the British might want to use it themselves.
The workings of the machine will be explained in later chapters. But for those as yet unfamiliar with the subject, it looked essentially like a small typewriter in a wooden box. On most models, there was a standard continental QWERTZU keyboard,
as opposed to the British QWERTY, and above that a lampboard with a series of lights, one for each letter of the alphabet. Inside the machine were a series of three, or sometimes four, rotors, which were the main elements of the encipherment system. The operator typed in the letters of the plain-text message. The action of depressing the key sent an electrical impulse through the machine and the enciphered letters lit up on the lampboard. On the later
Wehrmacht
models, there was a plugboard, or
Stecker
system, which increased the variations of encipherment to around 159 million million million possible settings. Put like that, it seemed impossible to break. But the reality was that there were still only twenty-six letters in the German alphabet and that gave the codebreakers a chance. Examining the commercial C Model he was given, where the number of different possible settings was merely several million, Foss decided that it had a high degree of security but, given certain conditions, it could be broken. If you knew a piece of original plain-text, a ‘crib’, that was at least 180 letters long, the wiring of the first two wheels could be worked out; and if the wiring was known, a crib of just fifteen letters would be sufficient to break the machine settings.
GC&CS did a very small amount of work on the machine during the early 1930s. But it was not until the Spanish Civil War in 1936 that there was any real attempt to break live Enigma traffic. After some initial work by Josh Cooper, an Enigma machine, given by the Germans to the Italians and Spanish (the K Model), was broken by Dilly Knox on 24 April 1937, using an improved version of the system recommended by Foss ten years earlier.
Here, in a paper written in September 1949, Foss describes the early British work on the commercial ‘C Model’ Enigma, and the beginning of the contacts with the French and Poles that were to become so important to the subsequent British breaks. The mention of the QWERTZU, or diagonal, in this paper is a reference to the order of the wiring between the keyboard and the first set of contacts inside the machine. The British had been unable to work out the order in which the keys were connected to the ‘entry plate’ in the
Wehrmacht
’s plugboard machine. Given the enormous number of different permutations available to the Germans, Foss and Knox had not imagined that it might simply
be in alphabetical order. This was probably the most important single piece of information that the Poles provided.
MS
My earliest recollections of the Enigma date back to 1926. We then knew of two models: large typing [B model] and small index [C model], I never saw the large machine and don’t know if it was ever widely used. It was the small index model that was later developed and used by German services and others.
It will be best to dispose of the large Enigma in a few paragraphs to avoid confusion. Its UK patent specification was 231,502, application date 25 March 1925, convention date (Germany) 25 March 1924. A letter from the Aeronautical Committee of Guarantee, Berlin, to the Air Ministry, dated 19 June 1924, said: ‘The invention, in an incomplete state, was examined in about 1921 by Lieutenant Hume, Office of the Military Attaché, British Embassy, Berlin, and it is believed, an expert was sent out from the War Office.’
[A letter from] Hume to [Edward] Travis, 29 July 1926, says that the company have informed him that they have sold out all the big machines and no more of this pattern will be manufactured. An improved model may be ready in 10 months’ time. Perhaps the Admiralty would meanwhile like to buy a model of the small machine. The improved model of the large machine was on view in 1928.
There is a brochure in French ‘
La Machine à Chiffrer, Enigma’
issued by
Chiffriermaschinen Aktiengesellschaft
, Berlin W, 35 (undated, but presumed about 1924). This deals with the machine from the user’s point of view and gives no details (apart from the usual astronomical number of key variations) of the ciphering. There is also a brochure in German.
An undated report describes a demonstration of the large machine at the Foreign Office on 27 March (possibly 1926). It was a typewriting model (called the ‘Typing Machine’ as opposed to the small ‘Index’ machine) and worked from the main current (DC). It had previously been demonstrated in Stockholm. It was a one-way machine (i.e. it had no reflector wheel), with four drums which were moved by four ‘gap-tooth’ cog wheels with different numbers of teeth on each, some of the teeth being operative and others not.
Sometime in 1927 or so Travis gave me a small machine to examine. I was not told where it came from, but presumed it had been bought
as a sample. This was the Enigma referred to [in the GC&CS history]
German Abwehr Cryptographic Systems and their Solution
vol. 1
(The Unsteckered Enigma).
A worker [Keith Batey] on the SD (
Sicherheitsdienst
) Enigma having recovered the upright, the next most natural step to take was to see whether any known machine had a wheel defined by this upright. This led to a most surprising discovery: that the wheel recovered was identical with wheel I of a certain commercial machine said to have been purchased by Mr [Dilly] Knox in Vienna in 1925. It had in fact been lying in a cupboard behind the person who made the original break.
The only difference between the two machines was that the turnover notch had been transferred to the tyre [ring] [in the SD machine]. I don’t know when this model [the small (Index) machine] was first made. It had movable tyres but the turnover notch was on the wheel and not on the tyre. Incidentally, the Air Ministry used this model as an inspiration for Typex
*
which also had turnover notches on the wheel and not on the tyres.
I wrote a paper entitled ‘The Reciprocal Enigma’ (the large Enigma was not reciprocal) in which I showed how, if the wiring was known, a crib of fifteen letters would give away the identity and setting of the right-hand wheel and how, if the wiring was unknown, a crib of 180 letters would give away the wiring of the right-hand and middle wheels. The methods I used were rather clumsy as they were geometrical rather than algebraical and, when Dilly Knox came to study the subject ten years later, he invented the ‘rods’ and the process known as ‘buttoning up’, which used the same properties as I had done, but did so in a more effective way.
In January 1939, the French cryptanalysts showed Denniston, Knox and myself their methods, which were even clumsier than mine, and ended with a flourish and a dramatic ‘
Voici la méthode Française
’. They asked Knox if he had understood and he replied in a very bored way
‘’Pas du tout’
, meaning (I think) ‘
Pas du tout à fait
’ [sic]. Denniston and I rushed in with conciliatory remarks. The French were, however, delighted with the rods when Knox explained them and by the next interview had made a set of ‘
réglettes
’ of their own.
At these two interviews, the Poles were mainly silent but one of them gave a lengthy description in German of the recovery of throw-on indicators when the operators used pronounceable settings. During this exposition Knox kept muttering to Denniston, ‘But this is what Tiltman did’, while Denniston hushed him and told him to listen politely. Knox went and looked out of the window.
Some time in 1938 or 1939, I can’t remember when – Josh Cooper places the time as the autumn of 1938 and that suits me – we were given by the Poles or French cribs of four long steckered Enigma messages and, I believe, the
Stecker
-pairings. I think that at the time we did know how the
Stecker
worked, but I can’t remember who told us. There is an undated translation of a secret German document published in 1930 which describes the method of plugging of the
Stecker
, but does not give the cryptographic effect. This may have been the document given us by the French in 1931. Knox, [Oliver] Strachey, R. R. Jackson and I all worked on it in an effort to reconstruct the wiring, including the basic ‘diagonal’, which on the steckered Enigma was ABCD … Z and not QWERTZU … I don’t know why the others failed, but the reason I failed was because I assumed the turnover notch was on the wheel and not on the tyre. I believe Knox and Strachey were allowing for the turnover notch to be on the tyre. Later on, at Warsaw, the Poles, who must have considered us all very stupid, gave us the complete answer.
*
The high-grade cipher machine used by the British armed forces during the Second World War