Celebrating Colossus, the codebreaking computer

Colossus computer at Bletchley Park
The Colossus was developed to break the Lorenz cipher

The BBC has a very interesting article and video about Colossus – the world’s first programmable, electronic, digital computer, developed to break WW2 era encryption.

In early World War 2, crypto-analysts working for British and Polish intelligence (the most famous of whom is probably Alan Turing) made great progress in breaking the German Enigma cipher, codenamed Ultra. However, in 1940 the Allies faced a significant problem as the Germans gradually switched to a new cipher – code-named Tunny. Created by the Lorenz cipher machine, this new cipher was orders of magnitude more complex than Enigma, and cut off the Allies’ source of intelligence.

German Lorenz SG40 cipher machine
German Lorenz SG40 cipher machine proved challenging for Bletchley Park

A lucky break came in 1941 when a Lorenz operator made a security related blunder (people are always the weakest link in the security chain!), allowing British cryptoanalysts John Tiltman and Bill Tutte to recover a plaintext sample and, in a brilliant intellectual feat, reverse engineer the Lorenz machine. However, with the basic electro-mechanical machines available at the time, it could still take 8 weeks to decipher a Lorenz message – far too long to be of any use.

Enter Colossus, the world’s first programmable computer, designed by Tommy Flowers and completed in 1944, shortly before the D-Day landings. Each Colossus consisted of 1,500 glass vacuum tubes performing the work which today would be performed be transistors. The machine was so secret that its existence – and the work of the men and women at Bletchley Park – was not made public until decades later.

Today encryption is used by computers every day – from protecting your login details to sending secure financial and government communications, encryption helps secure users against fraud and protect their privacy.

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