Researchers Decrypt Coded Letters Written by Mary, Queen of Scots

Researchers Decrypt Coded Letters Written by Mary, Queen of Scots

A computer scientist, a musician, and a physicist enter the archives of a national library. It sounds like the beginning of a joke, but the punchline is a serious one: Researchers of various backgrounds managed to find and decipher 57 letters written by Mary, Queen of Scots during her imprisonment by her cousin Queen Elizabeth I.

The letters date from 1578 to 1584, shortly before Mary was beheaded on February 8, 1587. Mary was convicted of endorsing an assassination plot against Elizabeth I, her cousin. The deciphered letters included about 50,000 words and 50 previously unknown scripts employed by Mary when communicating with her associates in code. The team’s research is published today in Cryptologia.

“To crack the code, we used a technique called hill climbing, from the domain of optimisation problems. We start with a random key, decipher the ciphertext with that key, make some small change in the key, and decipher again,” said George Lasry, a computer scientist and a member of the DECRYPT project, in an email to Gizmodo. “If the decryption is better, we keep the change. Otherwise, we discard the change.”

Lasry and his collaborators — Norbert Biermann, a music professor at Universität de Künst Berlin, and Satoshi Tomokiyo, a physicist and patents expert — were sifting through the Bibliotèque nationale de France’s online archives for enciphered letters. (The library is full of valuable written documents of historical significance, from Marie Curie’s radioactive notebook to Korean woodblock-printed documents, some of the earliest documents ever printed.)

A graphic showing some terms and parts of speech with their corresponding ciphered symbol. (Graphic: 2022 Lasry, Biermann, Tomokiyo)
A graphic showing some terms and parts of speech with their corresponding ciphered symbol. (Graphic: 2022 Lasry, Biermann, Tomokiyo)

The trio came across several uncategorized, ciphered documents listed by the library as early 16th-century works related to Italy. But looking into the documents, the researchers found that they were in France and had nothing to do with Italy.

Lasry said that the team’s eureka moment was finding the name ‘Walsingham’ in the letters. Francis Walsingham was the principal secretary of Elizabeth I, and his team decrypted enough of Mary’s correspondence during her imprisonment to build a case for the Catholic royal’s execution. The team wrote in their paper that Walsingham is “frequently mentioned in the letters, Mary warning Castelnau of his schemes in France and Scotland, describing him in negative terms, as a cunning person, falsely offering his friendship while concealing his true intentions.”

Mary also reacts to the kidnapping of her teenage son, James. “A series of letters from the second half of 1582 highlights Mary’s frantic response to the news on the abduction of her son James by a Scottish faction (the Ruthven Raid), desperately asking for help from France. When the French king finally sends an envoy to Scotland, Mary expresses her dissatisfaction at the results and her feeling that she and her son have been abandoned by France,” the team described.

“This is only the first phase of the project,” Lasry said. “We are very much looking forward to seeing what insight historians will be able to extract from those letters.”

The work is time-consuming. The 57 letters contained about 150,000 individual characters to work through; transcription of the documents took longer than the codebreaking, Lasry said.

Libraries are a great place to hold documents for safekeeping (with the notable exception of the Library at Alexandria). However, remarkable materials can be lost and forgotten in the vast collections. Two years ago, researchers found a rare version of the King Arthur legend in a Bristol library, penned 800 years ago. And last year, researchers found doodles by a woman named Eadburg in an 8th-century Old Testament manuscript.

With more scrutiny of the Mary letters, more details may emerge about her time imprisoned and the amount she knew about work being done on her behalf by her collaborators.

More: How Did Mary Queen of Scots Send Secret Messages?

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