Encrypted letter from Emperor Charles V finally deciphered after five centuries | Science

Charles V was one of the most powerful people of the sixteenth century. He led a gigantic empire that covered much of Western Europe and the New World during a reign of more than 40 years.

In 1547, Charles V sent a letter to Jean de Saint-Mauris, his ambassador to France. The tumultuous period was marked by a succession of wars and tensions between Spain and France, then ruled by Francis I.

Charles V’s letter, written in code, has been kept for centuries in the Stanislas library in Nancy. Cécile Pierrot, cryptographer at LORIA – the Laboratoire lorrain de recherche en informatique – first heard about the existence of the letter during a dinner in 2019. After much research, she finally got hold of it in 2021. The letter was signed by Karel V , but its mysterious contents were incomprehensible, according to Pierrot. It took a LORIA team six months to decipher the letter.

Using computers, Pierrot managed to identify “different families” of some 120 symbols used by Charles V. “Whole words were encoded with a single symbol,” and the emperor replaced vowels that came after consonants with other characters . For this he was probably inspired by Arabic, according to the cryptographer. In addition, he also used meaningless symbols to mislead opponents who would try to decipher the message.

The real breakthrough came in June, when Pierrot managed to decipher one sentence of the letter. The team then managed to crack the code with the help of historian Camille Desenclos. “It was painstaking and lengthy work, but there really was a breakthrough that happened in one day where we suddenly had the right hypothesis,” she says.

Another letter from Jean de Saint-Mauris, in which the recipient had scribbled some sort of transcription code in the margin, also aided in decipherment. It is “rare for a historian to be able to read a letter that no one has been able to read in five centuries,” says Camille Desenclos.

Once deciphered, the letter confirms the deteriorating relations between Francis I and Charles V in 1547, despite the fact that they had signed a peace treaty three years earlier. The two monarchs remained very suspicious of each other and both made several attempts to weaken each other. The letter also revealed a rumor of an assassination attempt being planned against Charles V in France, according to Desenclos. Little was known about that rumor until now, but the letter illustrates the fear of the monarch.

Researchers now hope to identify other letters from the emperor and his ambassador to Europe, in order to gain a sense of Charles V’s strategy in Europe. “We will probably make many more discoveries in the coming years,” says Desenclos.