National Museum of Computing to hold live Enigma code-breaking demo with a Bombe

Turing-Welchman machine to do its thing – with original wartime operator present

The National Museum of Computing (TNMOC) is going to fire up its replica Enigma code-breaker to decrypt encoded messages sent from Poland – with an original wartime Bombe operator supervising the process.

The British museum's Bombe replica, recently moved into the original Block H building that housed the wartime Bombes, is a fully functional reproduction of the machines that broke Nazi Germany's Enigma ciphers during the Second World War.

The electro-mechanical computers were used to read military messages sent between high-ranking German commanders, giving Britain and its allies a vital insight into what the Germans were up to and what they were planning to do next.

As part of the World Computer Congress being held in Poland this Friday (21 September), the Bombe will be fired up and set to work decrypting messages sent from the eastern European country. While the machine does its work (this is 1940s technology, remember), participants in the conference will hear papers about cryptography, the Bombe and master codebreaker Alan Turing, who, along with Gordon Welchman, was one of the leading minds behind the creation of the original Bombes.

Ruth Bourne, a wartime Bombe operator, will be present at TNMOC on the day to verify the process as the operators attempt to find the key to decrypt the message traffic.

The Bombe was built on codebreaking principles developed by Polish cryptanalysts in the very early stages of the Second World War, before that country was overrun by the invading German forces. Fleeing codebreakers took their knowledge to Britain, where what we now call GCHQ set to work adding to the Poles' efforts.

The Enigma machine was the main cipher machine used by German signallers. It worked through three – later four or five – rotor wheels that determined how plain-text messages were enciphered ready for transmissions. At the heart of the German signals process was the sending of the enciphered key setting twice at the beginning of each message. Repetition of letters in that key allowed British cryptanalysts to analyse the text and start building machines to decipher German messages, figuring out the wheel settings for each day.

Interested folk can watch the challenge live from around 0830 BST on Friday on the World Computing Congress website. ®

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