Who Built The First Modern Computer?

Most people think it was an American team that built the first working computer. In fact, the world's first programmable digital computer was built in secret by the British in the Second World War at Bletchley Park. Bletchley is famous as the place where the Enigma cipher machine was broken: a task which they performed efficiently using a machine called a Bombe. However, the most important thing that Bletchley did was neither breaking the Enigma code nor creating the Bombes. Professor Nigel Smart, Head of the Department of Computer Science at the University of Bristol and an expert on cryptography tells us more.

Enigma and Lorenz

The Enigma machine was used by the Germans to encrypt low level secret communications, such as battlefield communications or communications to U-Boats. It was a mechanical device which operated on letters. An operator encrypted a message using a typewriter like interface and then the encoded message was sent using Morse Code.

The Lorenz machine was the machine used by the Germans for more strategic communication. It took as input a message encoded using what is called a Baudot code. Baudot code had been used for years for teleprinter communications, and is essentially a conversion of the message into binary (a "binary encoding"): 1s and 0s. The Lorenz cipher would then encrypt the message to produce another binary encoding of the message (but now a binary encoding of the encrypted message).

Since the Lorenz cipher worked on binary encodings it could process information much faster than the Enigma machine, since no one needed to type a message into the machine. The Lorenz cipher was used by Hitler to communicate between his centres of command. If the Allies could break into the Lorenz information they would know what Hitler and his followers were actually thinking.

A Toe In The Door

In breaking the Enigma machine the British had the advantage of actually having an Enigma machine which had been recovered by the Polish. When breaking into the Lorenz machine though, they did not have a clue how it worked at all. To make it worse still, picking up the airborn traffic was harder. Intercepting the remote binary signal produced by Lorenz machines was much more difficult than recognizing the Morse code used by the Enigma.

They worked out exactly how the Lorenz machine worked just from seeing scrambled messages

However, by setting up listening stations the British recovered enough messages for the British cryptographers at Bletchley to actually work out exactly how the Lorenz machine worked, without ever seeing one. It was an amazing intellectual feat.

The cryptographers at Bletchley also worked out how to break the machine using subtle statistical weaknesses of the machine. Unfortunately, to actually exploit the weaknesses they needed to process a large amount of data. A lot of calculations would need to be performed on a given target message quickly. After all cracking a message years after it was sent wasn't a lot of help.