The three-page letter of Charles V to his ambassador was written against the background of a fierce struggle against the rise of the Protestant religion. Cécile Pierrot, a cryptographer at the Loria lab in France, first heard of the letter’s existence in 2019 and finally managed to track it down two years later. She rotted in the basement of the historic library in Nancy. Pierrot immediately tried to decipher the coded parts of this letter, classified the various symbols and looked for clues. It turned out to be a very difficult task.

details of the study

• The letter contained about 120 encrypted characters. They did not use a simple letter representation, that is, the password did not consist in simply replacing one or another letter with an unknown symbol.
• Most represented letters or letter combinations, but others represented whole words. For example, the needle represented the English king Henry VIII.
• Vowels following consonants were replaced with diacritical marks, except for the letter “e” (the most common letter), which the coders avoided as much as possible.
• A few characters seemed to have no function.

Simply typing into a computer and telling it to decode it would literally take longer than the history of the universe.
– says Cecile Pierrot.

The great breakthrough came thanks to historian Camille Desenclos, who pointed to several other cryptic letters written and sent to the emperor, one of which turned out to be unofficially translated. Pierrot called this letter the “Rosetta Stone” and added: “That was the key. We could have gotten there without him, but it bought us a lot of time.”. The team hopes to find and translate other letters from the emperor and ambassador in the coming years.

What is the letter about?

Piero and his colleagues have not yet published the full translation, as they are currently working on an academic paper.

• The letter was written by a Protestant group called the Schmalkaldic League, after Henry VIII’s death, a few weeks before the uprising in Germany.
• Charles V expressed a desire to keep the peace with France to focus his resources on fighting in the league, hoping to keep the French and British from helping the latter.
• Charles V also mentioned rumors about himself. An initiative was being prepared by the Italian mercenary Pier Strozzi instructing his ambassador to learn as much as possible about the truth of these rumors.. Obviously, it was empty gossip – no assassination attempts were discovered.
• Eventually, the emperor devised a strategic response to the news that his nephew, Ferdinand of Tyrol, had to flee the uprising in Prague. He instructed Saint-Maurice to spread the word that Ferdinand had voluntarily left Prague to join his father, Charles V’s brother, in the campaign.