Emperor Charles V's secret code cracked after five centuries

Letter from 1547 reveals Spanish king’s fears of a French assassination plot against him

Cécile Pierrot, a cryptographer from Loria laboratory, holds an encrypted letter from Charles V.
Agence France-Presse in Nancy

Thu 24 Nov 2022 10.13 EST

A team of researchers have cracked a five century-old code that reveals a rumoured French plot to kill Charles V.

Charles – the Holy Roman emperor and king of Spain – was one of the most powerful men of the 16th century, presiding over a vast empire that took in much of western Europe and the Americas during a reign of more than 40 years.

It took the team from the Loria research lab in eastern 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 that 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 the Stanislas library in Nancy. Cécile Pierrot, a cryptographer from Loria laboratory, first heard of its existence at a dinner in 2019, and after much searching she was able to set eyes on it in 2021.

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