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The Enigma machine was famously used by the Germans to send encrypted messages during World War II, only for the code to be broken by Allied scientists at Bletchley Park. The device was created in 1918 and made commercially available in the 1920s. The German military saw its potential to scramble messages and commissioned further developments, which resulted in an arms race with the Allied cryptographers.
The machine uses rotating wheels to chew up text and spit it out as ciphertext. The message can only be unscrambled if you know the setting of the Enigma's wheels and patchboard, which the Germans never realised can be deduced through mathematics, machinery, luck and poor operational procedures.
Photo credit: Science Museum
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