Here’s a French letter from the 17th century, encrypted probably in a homophonic system or a nomenclator. Can a reader decipher it?

Three months ago, I presented a terminology for codes and nomenclators, based on a workshop that took place at the HistoCrypt conference. After having received some interesting feedback, I can now provide an update.

For centuries nomenclators were the most popular kind of encryption. Still today messages enciphered with a well-designed nomenclator are hard or even impossible to break.

The British National Archive has published an encrypted letter from the 17th century. The solution is known, but many other encrypted notes of the same kind still wait to be broken.