King Louis XIV's Great Cipher System has given decoding experts a headache for more than two centuries

For centuries, the Great Code stood like an unassailable fortress, leaving even the most skilled codebreakers confused and even at a loss.

In the secret corridors of 17th century France, a cryptographic system called the Great Cipher - appeared and attracted great attention when it was created for King Louis XIV of this country. The two authors of the Great Code are the cryptographic genius brothers Antoine Rossignol and Bonaventure Rossignol , two brothers recognized for their exceptional skills in the field of cryptography. The person who appointed them to the position of royal cryptographer was King Louis XIV, who was nicknamed "Sun King" , ruling France from 1643 to 1715. This cryptographic system was Used to secure important French diplomatic and military communications.

 King Louis XIV (left) and Antoine Rossignol.

The mysterious legacy of the Rossignol brothers

The Rossignol brothers, who were appointed royal cryptographers by Louis XIV in the 17th century, came from a family of cryptographers. The family first came to royal attention when a young mathematician named Rossignol deciphered the Huguenot cipher during the siege of Réalmont in 1626, forcing the enemy to surrender. This brought him to the attention of Louis XIII's Premier, Cardinal Richelieu. Realizing the value of cryptographers to diplomacy and intelligence, Louis XIII declared on his deathbed that Rossignol was "most essential to the interests of the state".

 Cryptography is extremely important for diplomacy and intelligence - (Illustration).

During the reign of Louis XIV, Antoine and Bonaventure often worked in the room next to the king's study at Versailles and here they developed the Great Code for King Louis XIV. Thanks to that, they gradually wield great power when they can operate in a position of great power, running the Cabinet or the French Black Chamber - an international term referring to the crypto office. 

The Rossignol brothers' great cipher used a combination of homophones (symbols for the same sound) and polymorphisms (multiple symbols for each letter) , making it a system extremely complicated. Instead of using traditional letters, this code replaces various symbols and shapes with different sounds, adding an extra layer of complexity. This detailed design leaves modern code breakers almost at a loss.

 One of many nomenclatures used to encode the Great Cipher.

Successfully solved the seemingly impossible to crack code: The Great Code

For centuries, the Great Code has left many famous cryptographers scratching their heads. However, the mystery began to unravel in the late 19th century when Étienne Bazeries , a French military officer with a keen interest in cryptography, accepted the challenge of solving it. After three years of tireless effort, Bazeries successfully decoded the Great Code in the early 1890s, revealing the secrets hidden in its complex patterns. This achievement is a breakthrough in the history of human decoding.

Cracking the Great Code provided unprecedented access to the secret communications of French monarchs, diplomats, and military leaders. From there, we can understand the geopolitical context of Europe in the 17th century and shed light on the multidimensional relationships between European powers.