He was named sworn enemy of Francis I : Charles Fifth o Charles V (1550-1558) was the most powerful European ruler of the first half of the 16th century, headed by seventeen crowns from all over the continent. However, for several centuries, the contents of a letter encrypted and signed with his name remained secret from the eyes of historians. But after six months of investigations and analyses, computer science and history researchers finally reveal the meaning of the document, kept at the Stanislas library in Nancy (Meurthe-et-Moselle) all this time. An unprecedented discovery, “exceptional testimony of the situation in Europe” of that time, they wrote in a Nov. 23, 2022 press release.
Encrypted letters in a context of tensions
In 1547, when the letter was written, the emperor of the Holy Roman Empire was still in full confrontation with the French sovereign, through the Italian wars – whose Battle of Marignanoin 1515 is a landmark. At the same time Charles Quinto also clashes with the Lutheran princes in the Smalcalda war. The beginning of the year is finally marked by the death of the King of England Henry VIII , ceding the throne to Edward VI, then nine years old. In this context of intense tensions in Europe, it was therefore essential that the monarchs could communicate without their political opponents being able to intercept and decipher the messages, which explains the mysterious symbols of the letter studied here.
Five centuries later, researchers from the University of Lorraine, LORIA/INRIA, the CNRS and the University of Picardy Jules-Verne (CHSSC) studied one hundred and twenty of them. Only three short passages were written in the usual alphabet. And while cryptographers and computer scientists Cécile Pierrot, Pierrick Gaudry and Paul Zimmermann thought they could crack the document quickly, they eventually discovered a highly evolved encryption system for the 15th century. The easily identifiable letters have been deleted by breaking the “statistical aspects” that allow their recognition. For example, since the “qu” and “e” are easily associated, the author has taken great care to disguise them.
Charles V’s concerns revealed
But if they gradually figure out the rest, thanks to an algorithm that allows them to test hypotheses of correspondence among others, they struggle to find meaning in the text. This is where Camille Desenclos comes into play, at the time a specialist in relations between the two territories, also interested in cryptography in 16th and 17th century France, who in addition to helping to recontextualize it, directs the research on the addressee of the letter, Jean de Saint-Mauris , the ambassador of Charles V al King of Francefrom 1544. A letter of his, preserved in the Municipal Library of Besançon (Doubs), encrypted in the same way and mainly including a form of transcription in the margin, allows the entire code to be unlocked.
With this veil lifted, scholars acquire the precious content of the letter, written on February 22, 1547 – the date indicated on the document is 1546, because then an old calendar was used whose years began at Easter. It reveals three of Charles V’s concerns about France: “keep the peace with Francis I, avoid assassinations and put an end to the conflict between him and the Smalkalde league”, they say. After asking his ambassador to keep him informed of French political developments, the emperor reported that Francis I’s warlord Pierre Strozzi was trying to assassinate him. Rumor that Jean de Saint-Mauris formally denies in another letter.
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Rich in information on the situation in the mid-16th century and on the dynamics between these different powers, the deciphered document is in fact part of a much larger correspondence of hundreds of letters exchanged between the two men. The analysis of this communication could allow to obtain “a photograph of Charles V’s strategy in Europe”according to the decryptors, who hope to make more similar discoveries in the “secret” archives.
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