Imitation of Turing

I watched The Imitation Game last weekend. Benedict Cumberbatch did a good job of not playing the somewhat autistic Alan Turing just like his somewhat autistic Sherlock Holmes. All the actors played their parts well, and the film was very believable, though not quite accurate.

Early on in the film, Charles Dance’s character, Major Denniston, interviews Turing and tells him, “Enigma isn’t difficult, it’s impossible. The Americans, the Russians, the French, the Germans, everyone thinks Enigma is unbreakable.”

In reality, three Polish cryptologists, taking advantage of poor German operating procedures, had broken Enigma in 1932, long before WWII. They even designed a bomba kryptologiczna (cryptologic bomb) machine for breaking ciphers faster. Six were built. But enigma devices were then made more complex, and decryption became increasingly difficult and expensive. So the Poles shared their techniques with the French and British.

In the film, Turing joins the British team under Hugh Alexander (Matthew Goode) after the war has started, dismisses the team’s cryptological efforts as too slow, and by letter implores First Lord of the Admiralty Winston Churchill for funding to build a codebreaking machine, a forebear to the modern computer. After the machine itself, which he names after a schoolboy crush, proves still not fast enough to perform the bazillions of operations required to crack an Enigma cipher, Turing is accidentally inspired to start the machine searching for expected words and phrases, like Heil Hitler, which codebreakers called ‘cribs’.

In reality, Turing had been working with the British government for at least a year before the war, using cribs and building on the work of the Poles. In addition to many theoretical strategies, Turing conceived of a new ‘bombe’, a machine that could decrypt Enigma with what we now call more brute force methods than the Polish bomba, but which were still based on looking for a crib. One was built, and was successful, and a few more were built. He, Alexander, and the team together wrote a letter to Churchill asking for additional funding to build many more such machines. Along with the two hundred bombes approved by Churchill, British intelligence never stopped using cribs, and exploiting other German slipups, for every small advantage they could get.

While watching the film, I was wondering if the presence of Keira Knightley as Joan Clarke was a romantic fabrication, but Clarke was actually a very real and highly-regarded cryptanalyst at Bletchley, was briefly engaged to Turing despite knowing about his homosexuality, and did remain his friend after he broke it off.

Of course I recognized Allen Leech, who played Tom Branson on Downton Abbey, and Charles Dance, who played Tywin Lannister on Game of Thrones, but I didn’t recognize Matthew Goode as having played Ozymandias in Watchmen, though he did look familiar.


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