Great Cipher

In the history of cryptography, the Great Cipher or Grand Chiffre was a nomenclator cipher developed by the Rossignols, several generations of whom served the French Crown as cryptographers. The Great Cipher was so named because of its excellence and because it was reputed to be unbreakable. Modified forms were in use by the French Peninsular army until the summer of 1811, and after it fell out of current use many documents in the French archives were unreadable.

Historical background

Antoine Rossignol's cryptographic skills became known when in 1626 an encrypted letter was taken from a messenger leaving the city of Réalmont, controlled by the Huguenots and surrounded by the French army. The letter told that the Huguenots would not be able to hold on to the city for much longer, and by the end of the day Rossignol had successfully deciphered it. The French returned the letter with the deciphered message, forcing the Huguenots to surrender. He and his son, Bonaventure Rossignol, were soon appointed to prominent roles in the court.