57 letters by Mary Queen of Scots decoded 436 years after execution

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In a ground-breaking discovery, more than 50 letters written by Mary, Queen of Scots, during her imprisonment, have been decoded by the expert team at the DECRYPT project - 436 years after her execution on February 8, 1587.

57 documents with unknown ciphers were found during a search in the archives of the French National Library.

Lead author, computer scientist, and cryptographer George Lasry said, "Upon deciphering the letters, I was very, very puzzled and it kind of felt surreal," adding, "We have broken secret codes from kings and queens previously, and they’re very interesting but with Mary Queen of Scots, it was remarkable as we had so many unpublished letters deciphered and because she is so famous. This is a truly exciting discovery."
 
The letters were decoded through the use of computerized cryptanalysis, manual code-cracking, and linguistic and contextual analysis, as they contained more than 150,000 graphical letters in total that required a special graphical user interface tool to crack - and were unauthored. 

Spies, conspiracy and marriage

Decoders found out that the letters were penned by Mary to Michel de Castelnau, the French ambassador at the time, and the team was able to identify names, locations, and dates. 

54 of the 57 letters were written to Castelnau between May 1578 and May 1584, and 11 of the deciphered letters are dated between the years 1580-1581.

Their content includes Mary's suggestions on how to secure communication to safeguard her allies in France, alongside Elizabeth I's marriage, and a warning to Castelnau about Elizabeth's plans to destroy France. She also accused the Earl of Leicester of conspiring against her and Elizabeth's unwillingness to free her from prison.

Other letters show Mary's disapproval of Elizabeth's spy, Walsingham, as she warns that those working for Mary may be his agents. 

Lasr concluded, "In our paper, we only provide an initial interpretation and summaries of the letters. A deeper analysis by historians could result in a better understanding of Mary’s years in captivity," as he continued, "It would also be great, potentially, to work with historians to produce an edited book of her letters deciphered, annotated, and translated."