Charles V's letter finally deciphered | Tangente

Charles V's letter, readable at last

An encrypted letter from Charles V (1500–1558), Holy Roman Emperor, addressed in 1547 to Jean de Saint-Mauris, his ambassador to the king of France, and housed in the autograph collection of the Bibliothèque Stanislas in Nancy (Meurthe-et-Moselle), has just been not merely read but deciphered. Long passages in the letter are encoded.

Written by

ELISABETH BUSSER

PublishedFebruary 23, 2023UpdatedSeptember 19, 20261 min read

A team of researchers from Lorraine spent several months solving the puzzle. To do so, cryptographer Cécile Pierrot, mathematician Pierrick Gaudry, computer scientist Paul Zimmermann and historian Camille Desenclos drew on other ciphered dispatches sent to the same ambassador and held at the Bibliothèque municipale de Besançon (Doubs). Fortunately, several symbols appeared in cleartext in the margins to make these dispatches easier to decipher. These valuable clues gradually helped them reconstruct the entire cipher Charles V had used in his letter. It reveals that the emperor was suspicious—wrongly—of the king of France: he suspected Francis I^st of plotting to have him assassinated.

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Extract from Charles V's letter.

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