This time four summers ago, I was visiting the Foreign & Commonwealth Office while in London. It had been built during Queen Victoria’s reign to be the India Office, and while its Dunbar Court and mahogany council chambers were impressive, what I remember best about my time there was a vitrine.
The display case sat in a quiet room just across from 10 Downing St but while others peeked through blinds to see the prime minister’s residence, I was looking at a curious typewriter and red leather box inside this glass cabinet. A sheet of paper above it read:
“Originally designed in 1919 for commercial use, by the early 1930’s the ‘Enigma’ cipher machine was widely used by the German armed forces. Though similar in appearance to a typewriter it did not print anything. In 1926 there was even British interest in purchasing the machine but the Government Code and Cipher School, GCHQ’s predecessor, advised against this as it was slow to operate.
When a key is pressed it creates an electrical pulse that flows through the scrambler wheels before being turned back by a reflector to return through the wheels via a different route. The letter appearing on the lampboard is the enciphered result of the depressed key.
Each time a key is pressed the right-hand wheel rotates 1 position, introducing a new circuit for each letter. After 26 keystrokes the middle wheel moves round one position. When it has moved 26 positions the final wheel moves 1 position.
Enigma machines were used extensively by all German forces throughout WWII. Despite the astronomical number of combinations which an Enigma machine was capable of producing, basic weaknesses in the system were exploited by Polish crytanalysts who gave the solution to Britain and France when war was approaching in 1939. Decryption of Enigma messages by British cryptanalysts was of crucial importance and historians believe that intelligence gained from breaking Enigma helped shorten the war by at least two years.
Modified from time to time, versions remained in use until about 1956.”
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