The files date from 1578 to 1584 and contained 57 documents, which were found using computerized cryptanalysis, manual codebreaking and contextual interpretation, experts said.
The epistolary collects texts that expose the poor health of the monarch and the terrible conditions of her life while she remained imprisoned in England, as well as the negotiations with Queen Elizabeth I for her release, according to researchers.
“We’ve cracked secret codes of kings and queens before, and they’re very interesting, but with Mary, Queen of Scots, it was remarkable…we cracked so many previously unpublished letters,” said George Lasry, a computer scientist and lead author of the study.
The material also revealed her mistrust of some English nobles and anguish over the kidnapping of her son James Charles Stuart in 1582, the researchers noted.
During the time in captivity, Mary I maintained communication with her allies through messengers.
Born in 1556, the monarch is best known for her attempt to repeal the Anglican Reform, which she had begun during the reign of her father, Henry VIII.