viewpoints VDOI:10.1145/3018994 Thomas Haigh Historical Reflections Colossal Genius: Tutte, Flowers, and a Bad Imitation of Turing Reflections on pioneering code-breaking efforts. AY 14, 2017, will be the 100th anniversary of the birth of someone you might not have heard of: William Thomas (“Bill”) Tutte. MDuring the Second World War he made several crucial contributions to decrypt- ing the Lorenz cipher used to protect the Nazi high command’s most cru- cial radio communications. This work provided the statistical method imple- mented electronically by Tommy Flow- ers, a telecommunications engineer, in the Colossus machines, which pio- neered many of the electronic engineer- ing techniques later used to build digi- tal computers and network equipment.a Myths of Bletchley Park The British code-breaking effort of the Second World War, formerly secret, is now one of the most celebrated aspects of modern British history, an inspiring story in which a free society mobilized its intellectual resources against a ter- rible enemy. That’s a powerful source of nostalgic pride for a country whose national identity and relationship with A scene from the 2014 film The Imitation Game with actor Benedict Cumberbatch its neighbors are increasingly uncertain. portraying Alan Turing. Tutte’s centennial gives a chance to con- sider the broader history of Bletchley and the way in which it has been remem- ably comes from the Oscar-winning Park, where the codebreakers worked, bered. Some kinds of people, and work, film The Imitation Game. This gives us have become famous and others have a starting point: the film is a bad guide not. to reality but a useful summary of every- a This column draws on a research project in progress I am conducting with Mark Priest- Films reach more people than books. thing that the popular imagination gets ley, supported by L.D. Rope’s Second Chari- So statistically speaking, most of what wrong about Bletchley Park. PHOTO BY SNAP STILLS/REX/SHUTTERSTOCK BY PHOTO table Settlement. you know about Bletchley Park prob- One myth is that Alan Turing won JANUARY 2017 | VOL. 60 | NO. 1 | COMMUNICATIONS OF THE ACM 29 viewpoints Figure 1. Logical representation of the action of the Lorenz machine, dubbed “Tunny” by the when the correct settings have been British. The gap of four characters shown between the chi and psi wheels is to symbolize found. Enigma is broken! In reality this the idea of two logically independent transformations applied to a five channel bitstream, was not something that occurred to rather than a representation of the actual inner working of the machine. Turing only after he had finished build- ing a completely pointless machine, Source Lorenz Encoding Attachment but basic cryptanalytic practice already used to break Enigma manually. (paper 1 0 0 1 1 XOR χ1 1 0 1 1 XOR ψ1 0 0 0 radio tape or 0 1 0 1 0 XOR χ2 0 0 1 0 XOR ψ2 1 0 1 Even with the Bombe, breaking Enig- transmitter real time 0 1 0 0 0 XOR χ3 1 1 0 1 XOR ψ3 0 1 0 ma continued to rely on a mix of human keyboard 1 0 1 1 0 XOR χ4 1 0 1 0 XOR ψ4 0 0 0 skill, manual methods, and machine entry) 1 0 0 1 0 XOR χ5 1 0 0 0 XOR ψ5 1 0 1 power. Each Bombe was tended by a cipher text plain text µ1 µ2 (5 bit channels) (5 bit channels) team of female operators, and in recent 5 chi wheels 2 motor 5 psi wheels years a lot of attention has been paid to always wheels drive sometimes rotate psi wheels rotate the experiences of these women. The serialized Bombe operators and Enigma decryp- ciper text ters worked in factory-like conditions, Same wheel start positions and bit patterns used on encoding and decoding machines in a massive operation pioneered by Gordon Welchman for the group at- 01101 11101 01011 00101 tacking Air Force Enigma. Welchman Printer Lorenz Decoding Attachment had made his own vital contribution (Types out 1 1 0 0 1 XOR χ1 1 0 1 1 XOR ψ1 0 1 1 to the Bombe’s design, a “diagonal radio message 0 1 0 1 0 XOR χ2 1 0 0 0 XOR ψ2 1 0 1 receiver board,” but after the machines arrived as received) 0 0 0 1 0 XOR χ3 1 1 0 1 XOR ψ3 1 1 1 0 1 1 0 1 XOR χ4 1 0 1 0 XOR ψ4 0 0 0 shifted to overseeing their use. In con- 0 1 0 0 1 XOR χ5 1 0 0 1 XOR ψ5 0 0 1 trast, once logistical challenges began cipher text plain text µ1 µ2 to outweigh conceptual ones Turing drifted away from leadership of the corresponding group tackling Naval Enigma. There are many kinds of ge- the war pretty much by himself. Bene- and eventually triumphing. In reality, nius, and Turing’s was not of the mana- dict Cumberbatch played Turing as Turing was far from a marginal and de- gerial variety. television’s Sherlock: a humorless, asex- spised figure at Bletchley Park, moving By early 1945 more than 10,000 peo- ual loner whose superhuman mental quickly to a leadership role. The ob- ple worked directly on the British code- powers are compromised only by an stacles Cumberbatch faces are mostly breaking effort. Most of them were almost autistic indifference to social fictional and often absurd. His boss (in women. The film directs some heavy- norms. This combines the traditional reality Turing’s subordinate) Hugh Alex- handed sexism at Joan Clarke, a rare focus of popular science writing on ander tries to smash Christopher. Like female cryptanalyst, to give viewers a the lone genius who changes the world all military men Alastair Denniston, the chance to feel superior to their grand- with the modern movie superhero nar- head of Bletchley Park, is a belligerent parents. Word at Bletchley Park was rative of a freak who must overcome idiot. He smashes down the door, hop- indeed deeply stratified by class and his own flaws before he can save the ing to have Christopher destroyed. A gender, and cryptanalytic work of the world. (This is, I understand, exactly the little later Cumberbatch is blackmailed kind done primarily by upper middle same arc Cumberbatch follows in Doc- into passing secrets to a Soviet spy. class men like Turing has traditionally tor Strange, a literal superhero movie). Cumberbatch’s growth is symbolized been the most celebrated. Yet its own A team of six bright young men arrive by his making friends with the other erasure of the work routinely done by at Bletchley Park and are given the job brilliant codebreakers, but they seem women reflects a more modern sexism. of breaking the German Enigma code. just as arrogant as he was. Fearful that A single giant machine, given by a su- After introducing himself as “the best Bletchley Park managers will get in the perman, clunks without human inter- mathematician in the world,” Cumber- way, they pretend that Enigma is unbro- vention until the answer emerges. batch dismisses his fellow codebreak- ken and instead run the Battle of the At- That’s silly. So is the myth that bril- ers, saying “I don’t have time to explain lantic from their machine room, decid- liant scientists need no help from engi- myself as I go along, and I’m afraid ing which convoys to save and which the neers. Cumberbatch drew up the engi- these men would only slow me down.” U-boats should be allowed to sink. neering blueprints for the one and only Over their objections, and the opposi- Another myth is that code-breaking Bombe during a montage, then built it tion of almost everyone else at Bletch- machines eliminated human labor at Bletchley Park aided by a handful of ley Park, he designs a machine called and code-breaking skill. At first Chris- briefly glimpsed assistants. In fact, ap- Christopher to beat Enigma. topher spins uselessly, producing proximately 200 Bombes were manufac- The film struggles to shoehorn a dramatic tension but no Enigma set- tured, none of them at Bletchley Park, complicated, nuanced, and tragic sto- tings. At the last minute, Cumberbatch with design and production work done ry into the generic template of a hero thinks of looking for the common primarily by the British Tabulating Ma- overcoming obstacles, facing disaster, phrases, such as “Heil Hitler,” to detect chine Company, under the direction of 30 COMMUNICATIONS OF THE ACM | JANUARY 2017 | VOL. 60 | NO. 1 viewpoints its chief engineer Harold Keen. BTM had Tunny before Tunny, with the result that early licensed IBM punched card technology There’s another popular myth en- histories assumed that all intelligence for sale throughout the British Empire, dorsed by the The Imitation Game: that delivered by Bletchley Park had come giving it command of the necessary the Enigma was the only significant from Enigma. technologies and engineering methods. German cipher broken at Bletchley The British knew nothing about the In this way, and countless others, Park. In reality another cipher, code- machine producing Tunny, working technology transcended, rather than named Tunny, was just as important. entirely on clues from the intercepted supplemented, human labor and bu- Enigma was used by the German mili- messages. In contrast, the team break- reaucracy. Perhaps nobody would pay tary to communicate with forces in ing Enigma had a number of resources to see a movie centered on heroic pro- the field.