Turing’s rebuilt Delilah machine goes on public display for first time [Video]

A rebuilt version of Alan Turing’s Delilah encryption system went on public display for the first time as part of a special event organised by his nephew.

Sir Dermot Turing recently hosted the annual HistoCrypt event at Oxford University’s Kellogg College, Bletchley Park and The National Museum of Computing.

The three day event held last month was a focus on historical cryptology, which saw academic experts from across the world join VIP guests to see a showcase of artefacts and attend lectures.

In recent years, HMGCC has been home to the Delilah Rebuild Project, run by a team of volunteers led by John Harper. The rebuild project was based on original notes left by Alan Turing and engineer Don Bayley.

In 1943, Turing had visited Bell Labs in the USA where he saw a speech encryption system called SIGSALY, a device which demonstrated many firsts in communications technology.

By the time Turing returned to the UK, he had conceived the idea of a smaller secure speech system – Delilah.

By the end of World War 2, Turing and Bayley had succeeded in making a working prototype. They demonstrated the system in operation to high level visitors, usually by playing a Churchill speech recording through it.  

The HMGCC historian said: “The design of Delilah is highly innovative, applying knowledge that was not even in the textbooks of the day and it pushed the limits of the technology available at the time.

“Testing the rebuilt Delilah has been quite a challenge, even given the advanced test equipment available today, which has let us see exactly what the circuits are doing.”

A set of cipher wheels is one key part of Delilah, much like those in an Enigma machine. Engineers at HMGCC took on a special project to recreate the cipher wheels, tracking down information from the National Cryptologic Museum in USA. Thanks to information shared with HMGCC, engineers at Hanslope were able to manufacture the wheels to function in a rebuilt Delilah.

Sir Dermot Turing commented: “Delilah was invented by Alan Turing for making secure phone calls, so if you imagine a phone call as a piece of text to encipher, how would you do that with a voice message?

“What has been happening quietly behind the scenes is that a team led by John Harper and supported by HMGCC has been working together to bring Alan Turing’s machine back to life and we have been able to see this in operation. It was one of the most extraordinary things, to take this piece of 1940s technology and bring it back to life for us for the first time.”