Great Cipher

Antoine Rossignol's cryptographic skills became known in 1626, when an encrypted letter was taken from a messenger leaving the city of Réalmont, controlled by the Huguenots and surrounded by the French army.

In one of the encrypted letters between Louis XIV and his marshal Nicolas de Catinat appeared a possible solution to the mystery of the Man in the Iron Mask.

[2] The letter concerned a general named Vivien de Bulonde who was to attack the Italian town of Cuneo but instead fled, fearing the arrival of the Austrians, and consequently put in serious danger the success of the entire French campaign in Piedmont.

His Majesty desires that you immediately arrest General Bulonde and cause him to be conducted to the fortress of Pignerole, where he will be locked in a cell under guard at night, and permitted to walk the battlement during the day with a 330 309.The "330" and "309" codegroups appeared only once in the correspondence, so it is impossible to confirm what they stand for.

[9] Code sheets included alternative digits to modify the gender or letter case[10] and so the rules of French composition held true to encryptions as well.