Charles I’s secret code cracked

It was a mystery still unsolved. However, finally the truth was revealed. Who did it? Computer and history researchers. They unraveled an encryption code used five centuries ago. Thanks to them, the secret code of Charles I, Emperor of Spain and V of Germany, was deciphered. He used it to protect the secrecy of his letters. Not anymore.

Specifically, it was several months of research and analysis. This made it possible to unveil the mysteries surrounding a coded missive. It is preserved in the Stanislas Library, the municipal library of the city of Nancy, France.

The secret code of Charles I was deciphered and a letter from the 16th century could be read.
Charles I’s secret code was cracked and a letter from the 16th century could be read.

Hidden symbols

This is an unprecedented discovery. It is also an exceptional testimony of the situation in Europe in the 16th century. So say the authors of the study, reports the City of Nancy in a statement.

This encrypted letter was written in 1547. The emperor sent it to his ambassador to France, Jean de Saint-Mauris. It consists of sequences of letters and symbols interspersed with three short passages in plain text.

It was the heart of the Italian wars. They confronted the king of France Francis I to Charles V. The war of the Schmalkaldic League was in progress, in which Charles V was fighting with the Lutheran princes of the Empire. It had happened a few weeks after the death of Henry VIII of England. It was essential to be able to communicate without the adversaries being able to decipher the messages.

A team of cryptographers accomplished the feat.
A team of cryptographers accomplished the feat.

The secret language

The research team is led by Cécile Pierrot. She is a researcher in cryptography at Loria (Lorraine Research Laboratory). She resorted to data processing to find “different families” of about 120 symbols used by Charles V.

The researchers concluded that whole words are encrypted with a single symbol. Vowels coming after consonants were replaced with marks.

Meaningless symbols were also used. A letter from Saint-mauris on which the recipient had scribbled a code in the margin was used for the work. Eventually, the team managed to decipher a complete sentence from the letter. Slowly, Charles I’s secret code was deciphered. And the letter could be understood hundreds of years later.

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