Over 70 years ago, father of computer science Alan Turing developed the techniques which enabled quick and efficient decryption of the Nazis' Enigma-scrambled messages. Now, the secrets behind his techniques—hidden away in research documents since the Second World War—have been declassified.

Two papers were donated by the UK Government Communications Headquarters (GCHQ) to the British National Archive last week. Speaking to the BBC, a GCHQ mathematician, referred to only by the single name Richard, explained that the organization had "squeezed the juice" out of the two papers and was "happy for them to be released into the public domain".

They won't, however, be freely available online; anyone wanting to see the documents will have to make a trip to the National Archive at Kew, in the UK.

The documents themselves—produced on a typewriter and augmented with hand-written notes and algebra— are titled *On Statistics of Repetitions* and *The Applications of Probability to Cryptography*. The statistics paper deals with how repeated characters in two encrypted messages can be used to prove that both passages use the same encipherment key, while the cryptography essay is much longer, and covers in detail the methods of using probability theory to break codes. [BBC via The Register]

*Image from The National Archives*