The secret code of Emperor Charles V deciphered after five centuries | Spain

A team of researchers has cracked a five-century-old code that reveals a rumored French plot to kill the Roman emperor and king of Spain Charles V

Charles was one of the most powerful men of the 16th century, presiding over a vast empire that spanned much of the west Europe and the Americas during a reign of more than 40 years.

It took the team from the Loria research lab in the east France six months to decipher the letter, written in 1547 by the emperor to his ambassador in France. The tumultuous period saw a succession of wars and tensions between Spain and France, ruled at the time by Francis I, the Renaissance ruler who brought Leonardo da Vinci from Italy.

Charles V’s letter to Jean de Saint-Mauris had languished forgotten for centuries in the collections of the Stanislas library in Nancy. Cécile Pierrot, a cryptographer at the Loria laboratory, first heard of its existence during a dinner in 2019, and after much research, she was able to see it in 2021.

Bearing the signature of Charles V, it was both mysterious and completely incomprehensible, she told reporters on Wednesday.

Cécile Pierrot (L) and Camille Desenclos (R), lecturer in modern history, explain the process of decoding an encrypted letter from Charles V. Photography: Jean-Christophe Verhaegen/AFP/Getty Images

In painstaking work supported by computers, Pierrot found “distinct families” of about 120 symbols used by Charles V. “Whole words are encrypted with a single symbol” and the emperor replaced vowels coming after consonants by marks, she said, inspiration probably coming from Arabic.

In another obstacle, he used meaningless symbols to mislead any opponent trying to decipher the message.

The breakthrough came in June when Pierrot managed to decipher a sentence in the letter, and the team then cracked the code with the help of Camille Desenclos, a historian. “It was a long and painstaking job, but there was really a breakthrough that happened in one day, where all of a sudden we had the right hypothesis,” she said.

Another letter from Jean de Saint-Mauris, where the recipient had scribbled a form of transcription code in the margin, also helped.

Desenclos said that it was “rare as a historian to manage to read a letter that no one had managed to read for five centuries”. It “confirms the somewhat degraded state” in 1547 of relations between Francis I and Charles V, who had signed a peace treaty three years earlier, she said.

Relations were strained between the two, with various attempts to weaken each other. So much so that one nugget of information revealed was the rumor of an assassination plot against Charles V simmering in France, Desenclos said. “Not much was known” about the plot, but it underscored the monarch’s fear, she said.

The researchers now hope to identify other letters between the emperor and his ambassador, “to have a snapshot of Charles V’s strategy in Europe”.

“It is likely that we will make many more discoveries in the years to come,” added Desenclos.