During World War II, the Nazis used a machine called Enigma to turn their messages to each other into a code no one else could read.
Cracking Enigma, so spies could read the secret messages, was very difficult, but it became a lot easier with the invention of a machine called a Bombe. It worked a bit like an Enigma machine in reverse.
The bombe’s task was to find each day’s password. It was then easy to unscramble or decrypt all the day’s encrypted messages, and listen in on the Germans’ secret orders.
To work out the day password, the British spies at Bletchley Park had to find an encrypted version of a message they knew. For instance, they might look for a message that looked like an encrypted version of ‘I have nothing to report.’ (‘Keine besonderen Ereignisse’ in German). The fact that the Germans wrote Heil Hitler all the time helped too!
By the end of the war, cracking the day’s passwords had become a huge operation. Two thousand Wrens (women from the Royal Navy) were operating hundreds of bombes. The code cracking machines may have shortened the war by four years. But it wouldn’t have been as easy, if the Germans hadn’t been so predictable when using the machines.
Message that matters: cracking codes is easier if you know what you’re looking for
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