From ZDNet UK:

GCHQ has released two mathematical papers written by cryptographer Alan Turing after keeping the works secret for over half a century.

The intelligence agency believes the handwritten papers were produced by Turing during his time at Bletchley Park, the World War Two code-breaking centre, GCHQ said in a press release on Thursday. […]

One of the papers, the informal ‘Paper on Statistics of Repetitions‘, seeks a means to tell whether two enciphered messages with different plaintext and an overlap of characters used the same encipherment key during the overlap.

The second paper, ‘The Applications of Probability to Cryptography‘, was possibly written between April 1941 and April 1942, as it contains the reference ‘Hitler is now of age 52’. The paper uses probability analysis to look at four problems: ‘Vigenère’, ‘A Letter Substitution Problem’, ‘Theory of Repeats’, and ‘Transposition Ciphers’, said GCHQ. […]

The two papers have not been digitised, and only currently exist in handwritten form. People wishing to read the papers need to travel to the National Archives at Kew with the reference numbers of the papers, and two forms of ID — a picture ID, and proof of address. People who do this will probably be given a reader ticket number, which will then allow them to request the papers for viewing.