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An encrypted letter from Charles V deciphered by French researchers


Written in 1547 by the Emperor to his ambassador in Paris, the letter sheds new light on the relationship between the kingdom of Francis I and the Holy Roman Empire.

A series of " unintelligible

" symbols

which shed light five centuries later: four researchers presented their discovery in France on Wednesday, the deciphering of a letter written in 1547 by Charles V to his ambassador in Paris, shedding new light on the relations between the kingdom then led by Francis I, and the Holy Roman Empire.

To achieve this “


” feat, six months of work were needed for cryptographers from the Lorraine Computer Research Laboratory (Loria), associated with a historian from the University of Picardy, north of Paris.

Read alsoThe dream Europe of Emperor Charles V

The letter, forgotten for centuries, was in the collections of the Stanislas library in Nancy.

Cécile Pierrot, cryptographer at Loria, heard for the first time in 2019 of an "

encrypted letter from Charles V

" (1500-1558) by chance, during a dinner.

The researcher then believes in a legend, but when the existence of this document is mentioned to her again two years later, she decides to dig.

Word of mouth works, and at the end of 2021 she sees for the first time the mysterious and incomprehensible letter bearing the signature of the King of Spain, addressed to his ambassador Jean de Saint-Mauris.

Then begins the work of deciphering.

Cécile Pierrot observes the letter for a long time, classified “

by distinct families

» the 120 or so symbols used by Charles V.

She names them and decides to count their occurrences, to spot the combinations that could be repeated.

Read alsoThe broken dream of Charles V by Guillaume Frantzwa: glory and setbacks of the emperor

Diabolical encryption

To do this, she and two other researchers from the Nancy laboratory, Pierrick Gaudry and Paul Zimmermann, decided to use computers to “

accelerate research


No artificial intelligence, here it is the human who "

asks the right questions to the computer

", insists the cryptographer.

The deciphering is done "

small steps by small steps

", because the code used by Charles V is diabolical.

In addition to its large number of symbols, "

whole words are encrypted with a single symbol

" and vowels preceded by a consonant are marked by diacritics, an inspiration probably coming from Arabic, explains Cécile Pierrot.

The click finally happens at the end of June: Cécile Pierrot manages to isolate a series of words in the missive.

Le Figaro with AFP

Another confusing element, the emperor uses "

null symbols

", which mean nothing and in fact serve to mislead the adversary who would try to decipher the message.

The click finally happens at the end of June: Cécile Pierrot manages to isolate a series of words in the missive.

For this, the three cryptographers from Nancy called on Camille Desenclos, a specialist in both cryptography and relations between France and the Holy Roman Empire in the 16th century.

The historian helps them put the pieces of the puzzle together, recontextualizing the letter to better understand its allusions.

Degraded relations between Charles V and François 1er

A real "

Rosetta stone

" also helps the research: a letter from Jean de Saint-Mauris kept in Besançon, where the recipient had written in the margin "

a form of transcription

" by deciphering the missive sent to him by the ambassador , specifies Cécile Pierrot.

Once deciphered, the letter "

confirms the rather degraded state

" in 1547 of relations between François I and the Emperor of the Holy Roman Empire Charles V, who nevertheless signed a peace treaty three years earlier, explains Camille Desenclos .

Despite this peace, the two sovereigns maintain an "

extremely strong

" reciprocal "


" and seek "

to weaken each other

mutually, she adds.

Other information revealed by the deciphering of the letter: "

a rumor of an assassination plot against Charles V which would be brewing in France

", says Camille Desenclos, a rumor of which "

we did not know much

" before.

It will prove to be "


" - Charles V did not die assassinated - but this letter shows "

the fear

" of the prestigious monarch vis-à-vis this "

potential plot

", underlines the historian.

In his missive to his ambassador, the emperor also evokes the situation of his empire and his "

political and military strategy

": the use of encrypted correspondence thus allows him to "


» this particularly sensitive information to his adversaries.

The researchers now hope to be able to identify other letters in Europe from the emperor and his ambassador, "

to have a photograph of Charles V's strategy in Europe


Camille Desenclos is now sure of being able to continue to enrich historical research on this period: "

It is likely that we will still make many discoveries in the coming years


Source: lefigaro

All news articles on 2022-11-27

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