Adam talks to writer, broadcaster and all-round science guy Simon Singh.

Speaking at the Guernsey Literary Festival, Simon discusses his book 'The Code Book', and in particular the history of the Enigma machine, which the Germans used to encrypt their communications during World War II, and which was famously broken by Alan Turing and co at Bletchley Park.

How did Enigma work? How was it broken? And why did the story remain secret for decades?