More than 400 years ago, Mary, Queen of Scots was imprisoned in an English castle on charges that she’d conspired against Queen Elizabeth I, her cousin. As she tried to save her head, Mary wrote dozens of secret letters to friends and allies. In several of them, she discussed with France’s ambassador how rivals had abducted her son; in others she complained about conditions of her captivity and said she supported a controversial marriage that would’ve aided a political alliance between France and England.
Mary used a “spiral locking” technique to fold the letters, so the recipients would be able to tell if anyone had opened them before they were received. She and her associates also corresponded in a complex code, which protected the content for 436 years. Then in February, a group of codebreakers detailed in a paper how they’d designed a computer system to break it. In the paper, they showed how Mary had used a type of encryption known as a complex homophonic cipher, substituting various symbols for individual letters of the alphabet.
The researchers, part of a group of computer-savvy historians who call themselves the Decrypt Project, have spent the past decade poring over manuscripts from European archives, trying to solve hidden messages. The inspiration for the idea came in part from the 2011 cracking of the Copiale cipher, a 105-page collection of handwritten characters that German occultists wrote in the 1700s. Among the things depicted in those decoded manuscripts was an initiation ritual for a secret society that involved repeatedly asking recruits to read a blank piece of paper before plucking a single one of their eyebrows.
