Holy Roman Emperor Charles V used an ingenious code to keep his messages secret (Credit: AFP / Jean-Christophe Verhaegen)
A team of French researchers have cracked a secret code used by Holy Roman Emperor Charles V five centuries ago.
The emperor, and former King of Spain, used the code in a letter written during the height of his power in the 16th century. It was addressed to his ambassador in France in 1547 during a period of rising tension between France and Spain.
Following the death of British monarch Henry VIII, a key ally, Charles wanted the ambassador to report back on the military manouvres of French king Francis I.
But, because he was paranoid the letter could be intercepted, he designed a complex cipher to keep its contents private.
Historians have been puzzling over it ever since.
The code was finally broken after researchers from the Loria research lab in Lorraine, eastern France spent six months working on it.
To get to the bottom of it, cryptographer Cecile Pierrot ran the ten-page document through a statistical analysis program back in December 2021. But the first results suggested the computer would need a period of time greater than the age of the universe to unravel the code.
Cecile Pierrot (left) and Camille Desenclos (right) examine the letter dating back to 1547 (Credit: AFP / Jean-Christophe Verhaegen)
So she spoke with historian Camille Desenclos, who sent her to other letters from Charles V to his ambassador. One of these included a rough key to the code scribbled in the margin.
Following months of work, Pierrot then found ‘distinct families’ of around 120 symbols used by the emperor.
‘Whole words are encrypted with a single symbol,’ she told AFP.
Other tricks employed included replacing vowels after consonants with marks and just inserting random symbols into the text that meant nothing at all.
‘It was painstaking and long work but there was really a breakthrough that happened in one day, where all of a sudden we had the right hypothesis,’ Desenclos said.
Once they had decoded the message, it turned out that Charles had caught whiff of a rumoured assasination plot against him brewing in France. He wanted to know if there was any truth to it.
Researchers Cecile Pierrot (left) and Camille Desenclos (right) were the ones that cracked the code (Credit: AFP / Jean-Christophe Verhaegen)
Desenclos said ‘not much had been known’ about this rumoured plot before they decoded the letter, but it did hold true with the ‘fear’ Charles exhibited throughout his reign.
In the end, the Holy Roman Emperor died of malaria while secluded at a monestary having abdicated from his various roles.
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It’s straight out of a Dan Brown novel.
