Louis XIV’s Great Cipher Baffled Codebreakers Until the 19th Century
In the clandestine corridors of 17th-century France, a remarkable cryptographic system known as the Great Cipher emerged, becoming the go-to code for the French monarch Louis XIV. The genius behind this ingenious cipher was Antoine and Bonaventure Rossignol, two brothers recognized for their exceptional skills in cryptography. Appointed as royal cryptologists by the ‘Sun King’, who ruled France from 1643 until 1715, the Rossignol brothers developed the Great Cipher to protect sensitive diplomatic and military communications from prying eyes.
Antoine Rossignol, the cryptologist, who came to the attention of Louis XIII's chief minister, Cardinal Richelieu, when he cracked the code of a Huguenot cipher. Portrait by Charles Perrault. (Public domain)
The Cryptic Legacy of the Rossignol Brothers
The Rossignol brothers, who were appointed as royal cryptologists by Louis XIV in the 17th century, hailed from a family renowned for its exceptional skills in cryptography. The family first came to the attention of the royal family when a young mathematician named Rossignol managed to decipher a Huguenot cipher during the siege of Réalmont in 1626 leading to their surrender.
This brought him to the attention of the Louis XIII's chief minister, Cardinal Richelieu, who recognized the value of cryptologists for diplomatic and intelligence purposes. On his deathbed, Louis XIII reportedly stated that Rossignol was “most necessary to the good of the state.”
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In the era of Louis XIV, Antoine Rossignol and his son, Bonaventure, continued the family’s cryptology tradition. Often working in a room located next to the King's study at Versailles, they developed the Great Cipher of Louis XIV. This put them in a position of immense power, running what came to be known as the Cabinet noir, the renowned French Black Chamber, which became an international term for any code bureau.
The Rossignol brothers' Great Cipher employed a combination of homophonic (symbols for the same sound) and polygraphic (multiple symbols for each letter) elements, making it an exceptionally complex system. Instead of using traditional letters, the code substituted various symbols and shapes for different sounds, adding an extra layer of intricacy. This detailed design rendered the code virtually indecipherable to contemporary codebreakers.
One of many nomenclators used to encode the Great Cipher. (Public domain)
Cracking the Unbreakable Code: The Great Cipher
For centuries, the Great Cipher stood as an impenetrable fortress of secrecy, confounding even the most skilled codebreakers. However, the mystery began to unravel in the late 19th century when Étienne Bazeries, a French army officer with a keen interest in cryptography, took on the challenge.
After three years of relentless effort, Bazeries successfully cracked the Great Cipher in the early 1890s, revealing its inner workings and unlocking the secrets concealed within its intricate patterns. His achievement marked a groundbreaking moment in the history of codebreaking.
Cracking the Great Cipher provided unprecedented access to the confidential communications of French monarchs, diplomats and military leaders. The intercepted information proved instrumental in understanding the geopolitical landscape of 17th-century Europe and shed light on the nuanced relationships between European powers.
Top image: Mysterious eyes in binary code. The Great Cipher of Louis XIV had codebreakers stumped for centuries. Source: Kundra / Adobe Stock
