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Three other inventors in three other countries had independently and almost simultaneously hit upon the idea of a cipher machine based on rotating scramblers.
The American Black Chamber solved 45,000 cryptograms in a decade, but by the time Hebern built his factory, Herbert Hoover had been elected President and was attempting to usher in a new era of trust in international affairs. He disbanded the Black Chamber, and his Secretary of State, Henry Stimson, declared that “Gentlemen should not read each other’s mail.”
The first was Winston Churchill’s The World Crisis, published in 1923, which included a dramatic account of how the British had gained access to valuable German cryptographic material:
Also in 1923, the British Royal Navy published their official history of the First World War, which reiterated the fact that the interception and cryptanalysis of German communications had provided the Allies with a clear advantage.
These Enigmas were distinct from the few machines that Scherbius had previously sold to the business community, because the scramblers had different internal wirings.
Scherbius’s invention provided the German military with the most secure system of cryptography in the world, and at the outbreak of the Second World War their communications were protected by an unparalleled level of encryption.
It would appear that fear was the main driving force, and that adversity is one of the foundations of successful codebreaking.
However, in the wake of the First World War the Allies no longer feared anybody.
After the First World War, Poland reestablished itself as an independent state, but it was concerned about threats to its newfound sovereignty.
By selling secret Enigma information to foreign powers, Hans-Thilo Schmidt could earn money and gain revenge, damaging his country’s security and undermining his brother’s organization.
In general, it is true to say that if a single key is used to encipher an enormous quantity of material, then it is easier for a cryptanalyst to deduce it.
As an extra precaution, the Germans therefore took the clever step of using the day key settings to transmit a new message key for each message. The message keys would have the same plugboard settings and scrambler arrangement as the day key, but different scrambler orientations.
cryptanalysts were experts in the structure of language, but the arrival of Enigma prompted the Poles to alter their recruiting policy.
Rejewski’s strategy for attacking Enigma focused on the fact that repetition is the enemy of security: repetition leads to patterns, and cryptanalysts thrive on patterns.
As each new message is intercepted, it is possible to identify other relationships between the 1st and 4th letters of the repeated message key.
Although the plugboard and scrambler settings both affect the details of the chains, their contributions can to some extent be disentangled. In particular, there is one aspect of the chains which is wholly dependent on the scrambler settings, and which has nothing to do with the plugboard settings: the numbers of links in the chains is purely a consequence of the scrambler settings.
Rejewski had vastly simplified the task of finding the day key by divorcing the problem of finding the scrambler settings from the problem of finding the plugboard settings. On their own, both of these problems were solvable.
I have had to sum up his work in just a few pages, and so have omitted many of the technical details, and all of the dead ends.
Without the fear of invasion, the Poles would have been discouraged by the apparent invulnerability of the Enigma cipher. Without mathematics, Rejewski would not have been able to analyze the chains. And without Schmidt, codenamed “Asche,” and his documents, the wirings of the scramblers would not have been known, and cryptanalysis could not even have begun.
His old catalogue of chain lengths was useless, but rather than rewriting the catalogue he devised a mechanized version of his cataloguing system, which could automatically search for the correct scrambler settings.
The units were called bombes, a name that might reflect the ticking noise they made while checking scrambler settings.
By depriving Rejewski of the keys, Langer believed he was preparing him for the inevitable time when the keys would no longer be available.
Enigma operators were all given two new scramblers, so that the scrambler arrangement might involve any three of the five available scramblers.
The following month the situation worsened when the number of plugboard cables increased from six to ten.
Langer was determined that if Poland was invaded, then its cryptanalytic breakthroughs, which had so far been kept secret from the Allies, should not be lost.
The Poles were a decade ahead of anybody else in the world.
Polish progress had ground to a halt on the introduction of the new scramblers and extra plugboard cables, but the fact remained that Enigma was no longer considered a perfect cipher.
In Britain, Room 40 had always been dominated by linguists and classicists, but now there was a concerted effort to balance the staff with mathematicians and scientists. They were recruited largely via the old-boy network, with those inside Room 40 contacting their former Oxford and Cambridge colleges. There was also an old-girl network which recruited women undergraduates from places such as Newnham College and Girton College, Cambridge.
Turing knew of Babbage’s work, and the universal Turing machine can be seen as a reincarnation of Difference Engine No. 2. In fact, Turing had gone much further, and provided computing with a solid theoretical basis, imbuing the computer with a hitherto unimaginable potential.
Each day he cycled 5 km from Shenley Brook End to Bletchley Park, where he spent part of his time in the huts contributing to the routine codebreaking effort, and part of his time in the Bletchley think tank, formerly Sir Herbert Leon’s apple, pear and plum store.
was Turing’s job to find an alternative way to attack Enigma, one that did not rely on a repeated message key.
When a piece of plaintext can be associated with a piece of ciphertext, this combination is known as a crib.
He wanted to divorce the problem of finding the scrambler settings (finding which scrambler is in which slot, and what their respective orientations are) from the problem of finding the plugboard cablings.
Turing had constructed his electrical circuit in such a way as to nullify the effect of the plugboard, thereby allowing him to ignore the billions of plugboard settings.
In short, the plugboards cancel themselves out throughout the whole circuit, so Turing could ignore them completely.
In effect, there were now 26 electrical loops, and each one would have a lightbulb to signal the completion of an electrical circuit.
The combination of crib, loops and electrically connected machines resulted in a remarkable piece of cryptanalysis, and only Turing, with his unique background in mathematical machines, could ever have come up with it.
Each of Turing’s bombes was to consist of twelve sets of electrically linked Enigma scramblers, and would thus be able to cope with much longer loops of letters.
Turing finalized the design at the beginning of 1940, and the job of construction was given to the British Tabulating Machinery factory at Letchworth.
One of the features of the Enigma machine was its inability to encipher a letter as itself, which was a consequence of the reflector.
find the correct alignment, we simply slide the plaintext and the ciphertext relative to each other until no letter is paired with itself.
In fact, had the cipher machines been used properly—without repeated message keys, without cillies, without restrictions on plugboard settings and scrambler arrangements, and without stereotypical messages which resulted in cribs—it is quite possible that they might never have been broken at all. The true strength and potential of machine ciphers was demonstrated by the Typex (or Type X) cipher machine used by the British army and air force, and the SIGABA (or M-143-C) cipher machine used by the American military. Both these machines were more complex than the Enigma machine and both were used
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In Northern France during the First World War, Captain E.W. Horner of Company D, 141st Infantry, ordered that eight men from the Choctaw tribe be employed as radio operators.
For the Navajos, committing everything to memory was trivial because traditionally their language had no written script, so they were used to memorizing their folk stories and family histories.
advance. The marines radioed back in English explaining their position, but the salvos continued because the attacking American troops suspected that the messages were from Japanese impersonators trying to fool them.
A Navajo message could never be faked, and could always be trusted.
The impenetrability of the Navajo code was all down to the fact that Navajo belongs to the Na-Dene family of languages, which has no link with any Asian or European language.
If it became clear to the Japanese that words were being spelled out, they would realize that they could use frequency analysis to identify which Navajo words represented which letters.
The solution was to add more words to act as extra substitutes (homophones) for the commonly used letters.
Lieutenant General Seizo Arisue, the Japanese chief of intelligence, admitted that, although they had broken the American Air Force code, they had failed to make any impact on the Navajo code.
