Emperor Charles V’s secret code cracked after five centuries | Spain

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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 took in large parts of the western Europe and America during a reign of more than 40 years.

It took the team from the Loria research laboratory 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 series 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.

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

With Charles V’s signature, it was both mysterious and completely incomprehensible, she told reporters on Wednesday.

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

In painstaking work aided 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 after consonants with marks, she said, an inspiration likely coming from Arabic .

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

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

Another letter from Jean de Saint-Mauris, in which the recipient had written some sort of transcription code in the margin, also helped.

Desenclos said 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 deteriorated state” in 1547 of relations between Francis I and Charles V, who had signed a peace treaty three years earlier, she said.

Relations were tense between the two, with various attempts to undermine each other. So much so that one leak of information was the rumor of an assassination plot against Charles V said to have been brewing in France, Desenclos said. “Not much was known” about the plot, but it underscored the monarch’s fears, she said.

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

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

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