If you’re interested in the history of codebreaking or computers, you’ve probably heard of Alan Turing! (You’re also probably smarter than we are.) Born in 1912, Turing was a mathematician, computer scientist, and cryptanalyst, whose work with the Government Code and Cypher School during the Second World War was a major contributing factor in cracking the Germans’ supposedly unbreakable Enigma code. He was also a member of King’s College, Cambridge, both as a student and later as a Fellow of the college—so it seems only fitting that LockHouse should celebrate his remarkable achievements!

Turing’s life

A passport photo of Alan Turing aged 16Before attending Cambridge, Turing went to Sherborne School in Dorset. The first day of term coincided with the first day of the 1926 General Strike—but rather than risk missing term due to being unable to get there by train, the 13 year old Turing cycled all the way from Southampton to Sherborne, a distance of 60 miles. At Sherborne, his inclination towards science and mathematics clashed with the school’s encouragement of the Classics. In the sixth form, however, he met Christopher Morcom, a fellow bright student and science enthusiast. Morcom has been described as Turing’s first love, and his death a few years later in 1930 from tuberculosis was a severe blow to Turing.

Turing attended King’s College, Cambridge from 1931-1934. Upon his graduation, he was made a Fellow of King’s at age 22, thanks to the strength of his dissertation. He moved briefly to America, getting his PhD from Princeton in 1938, before returning to Cambridge. (Writing to his mother from Princeton, he commented on the conversation of his American acquaintances: ‘They seem, from what I can remember of it, to have discussed nothing but the different states that they came from.’) 

In 1952, Turing reported a burglary of his house. During the course of their investigations, the police discovered Turing’s relationship with Arnold Murray. Turing was charged with gross indecency, and made to undergo chemical castration as an alternative to being imprisoned. He died in 1954, having poisoned himself by ingesting cyanide. 

The cruelty and injustice which Turing faced in his lifetime were not formally addressed until the 21st century. Following an Internet campaign, then-PM Gordon Brown issued an apology in 2009. Turing was posthumously pardoned for his conviction in 2013, and the 2017 law pardoning all men convicted under legislation prohibiting homosexual acts is known as the Alan Turing law, enshrining Turing’s significance not only to science but to the history of LGBT+ equality. And we’ll be seeing Turing’s face more frequently in future—it was announced in 2019 that he’ll be commemorated on the new £50 note! 

Cracking Enigma

One of the things for which Turing is most famous is his codebreaking work during the Second World War. Turing worked with the Government Code and Cypher School from 1939, and was instrumental in helping to break Enigma.

Enigma was an encryption device used to encode and decode German transmissions. It was used by the German army, air force, and, crucially, the navy—with German submarines attacking British supply lines in the Atlantic, being able to decipher their transmissions and disrupt their operations became essential. 

Enigma provided a polyalphabetic substitution cipher. Its basic design resembled a typewriter with a corresponding set of light up letters. When a plaintext key was pressed, a corresponding letter would illuminate to form the ciphertext. What made Enigma so secure—and so difficult to break—was that it used a combination of three rotor scramblers (in the later stages of the war, randomly selected from a possible four or five). The rotors would turn each time a letter was entered, meaning that the cipher for each letter would change, and the number of rotors meant that the sequence took 16,900 characters to repeat—longer than any messages sent, which were limited to a few hundred characters. Later Enigma machines also had a plugboard, which connected pairs of letters via wires; these pairs of letters would be swapped before and after encryption, adding an extra layer of security. 

One of the main weaknesses of the Enigma was that no letter could be enciphered to itself—for example, an E in the plaintext couldn’t become an E in the ciphertext at any point. At Bletchley, Turing exploited this weakness in designing the bombe, an electro-mechanical device used to identify possible starting positions for the rotors and the pairs of letters for the plugboard. It did this by simulating the running of multiple Enigma machines, testing for viable possibilities — any potential starting position which led to a letter being enciphered to itself was a contradiction, and could be ruled out. In this way the number of potential correct starting positions could be reduced to a manageable number.

You can learn more about Enigma here, or encode and decode your own text with this online emulator!

What now?

If you’re interested in Alan Turing, computers, or codebreaking, there are a bunch of ways to learn more! The Imitation Game (2014) is a look at Turing’s work at Bletchley starring Benedict Cumberbatch. If you’ve already seen it, or are looking for something a bit less flashy, we recommend Breaking the Code, a 1996 television movie (adapted from a play) that features Derek Jacobi in a brilliantly emotional portrayal of Turing. Bletchley Park is open to visitors. Closer to home, you can visit the Centre for Computing History in Cambridge for a fantastic dive into all things computers, or wander by King’s College and try to spot the blue plaque commemorating Turing. 

Feel like putting your own code-cracking abilities to the test? Come by LockHouse and spend an hour solving puzzles in one of our escape rooms! And try your hand at solving this simple cipher for a special message:

tqh cjkh rtpaisojgoh lr cehcdjtr ujp rhi mhpchir kaqcjtir