Enigma cypher machine, c 1930s.

GERMANY - OCTOBER 23: Throughout WWII, Germany and its allies encrypted military communiques using Enigma machines and, by 1945, over 40,000 such machines were in use. The Germans considered the Enigma code to be unbreakable, but the codebreakers at Bletchley Park in Buckinghamshire, the British forces' intelligence centre, managed to decipher the code with the help of 'Bombe' codebreaking machines. This feat is said to have dramatically shortened the war. (Photo by SSPL/Getty Images)