Codebreakers Decipher Lost Letters of Mary, Queen of Scots

There are many historians who believe the Allies would not have won World War II without the help of more than 10,000 women who worked behind the scenes as key members of the wartime intelligence effort to break the codes of the German and Japanese militaries. While this effort is often met with surprise, it shouldn’t be – thousands of British women worked at Bletchley Park in England’s codebreaking unit to decipher codes from the German Enigma machine. So, it should come as no surprise that women are also adept at creating codes, not just breaking them. The news this week brings an outstanding and previously unknown historical example dating back to the 16th century and Mary, Queen of Scots. A team of code-breakers has deciphered 430-year-old letters written in code by Mary while she was imprisoned by her cousin, Elizabeth I. Did the team include any women?

“Mary Stuart, Queen of Scots (1542–1587), has left an extensive corpus of letters held in various archive collections. There is evidence, however that other letters from Mary Stuart are missing from those collections, such as letters referenced in other sources but not found elsewhere.”

Mary Stuart was only six days old when her father, James V of Scotland, died and she became queen. It took a few years for Mary to learn to write, but she soon became a prolific letter writer – leaving behind a vast collection of correspondence … much of it necessitated by the fact that she spent nearly two decades imprisoned by Elizabeth I to keep her from taking her throne away. While Mary thought for a time that her letters from prison were kept secret, they were not – and their contents were eventually used to justify her execution in 1587. Those letters have been studied by historians who concluded that some were missing. A new study published in the journal Cryptologia reveals how three people - George Lasry, a computer scientist and a member of the DECRYPT project (an open access project to release resources and tools to facilitate research in historical cryptology), Norbert Biermann, a music professor at Universität de Künste Berlin, and Satoshi Tomokiyo, a physicist and patents expert – were looking through enciphered letters in the Bibliotèque nationale de France’s online archives. What they found were a puzzling set of uncategorized, ciphered documents labeled as early 16th-century works from Italy. The puzzling part was that these documents were in French, not Italy. That was enough to inspire them to attempt to decode these 57 documents.

“Breaking the code was not a eureka moment — it took quite a while, each time peeling another layer of the ‘onion.’”

Lasry explained to CNN how the team started with computer algorithms, but managed to only decipher 30% of the text – not enough to identify it. That forced them to resort to use contextual analysis – manually analyzing the symbols. This tedious job involved transcribing the 150,000 ciphered letters, then interpreting them into 50,000 symbols. Each letter of the alphabet could be encoded with many cyphers, so they couldn’t be recognized by looking for simple patterns. (A graphic of some of these ‘homophones’ can be seen here.)  The team also found that some symbols represented common places, words and names. The discovery of one name in particular helped link the letters to Mary, Queen of Scots. That was ‘Walsingham’ –Francis Walsingham was the principal secretary of Elizabeth I. From that one name, Lasry’s team suspected that the letters had been written by Mary to the French ambassador, Michel de Castelnau, warning him not to trust Walsingham. Since there were other known letters between Mary and Castelnau, the team was able to find places that matched their deciphered material, which helped decode other symbols. That identified symbols for names, places, and the twelve months of the year -  and the puzzle was solved.

"Upon deciphering the letters, I was very, very puzzled, and it kind of felt surreal. 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. Together, the letters constitute a voluminous body of new primary material on Mary Stuart—about 50,000 words in total, shedding new light on some of her years of captivity in England."

While Lasry and his team solved one puzzle, they started a second – how did Mary, Queen of Scots, develop her own secret cypher that managed to defied decoding for over 400 years? According to Ars Technica, Mary learned the techniques from her mother, Marie de Guise, who learned the skills from a large group of royals, educators and scientists -- Elizabeth I, Catherine de Medici, Machiavelli, Galileo Galilei, John Donne, and Marie Antoinette, to name a few - who used various techniques to keep their correspondence secret. One was "letter-locking," where letters were folded and “locked” by inserting a slice of the paper into a slit, then sealing it with wax – a tear in the paper would indicate tampering. Mary herself used a sophisticated spiral letter-lock for her final letter to King Henri III of France on the eve of her execution.

Mary’s primary secret letter writing was to Castelnau – 54 of the 57 letters were to him between May 1578 and May 1584.  Mary used trusted couriers to deliver the letters, but Walsingham eventually found a mole in the French embassy who intercepted them and sent him copies. Mary obviously believed her code and couriers were secure – she wrote in the letters about a proposed marriage between Elizabeth I and the Duke of Anjou, which she warned would weaken France. She accused the Earl of Leicester and others of plotting against her and accused Elizabeth of not negotiating for her release in good faith – history shows that to be true.

One other new puzzle – the decoding team found chronological gaps which suggest there are more coded letters in the Bibliothèque Nationale de France and other archives. While the would like to search the actual papers – they only had access to digitized online copies- the team admits they only fully deciphered a small number of Mary’s letters due to the sheer volume and complexity of the 50,000 symbols.

And here’s one more puzzle – why didn’t this team include any women? Perhaps now that the masterful code-writing skills of Mary, Queen of Scots have been revealed, this and other deciphering projects will recruit the granddaughters and great-granddaughters of the women who broke the codes of World war II.