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The Great Cipher Mightier Than the Sword

In 17^th century France, a religious war raged between the ruling Roman Catholic French and the French Protestants, known as the Huguenots. In 1626, the Huguenots were under siege in the small town of Réalmont but rejected the royal army’s call to surrender. The Catholics faced a long battle with no signs of a breach in the Huguenots’ defenses until they intercepted an encrypted letter from the Huguenots meant for their allies. No one in the army could break the cipher until they sent it to Antoine Rossignol, a mathematician in a nearby town who deciphered the letter, revealing the Huguenots desperation for supplies and ammunition. The Huguenots surrendered shortly afterward and Rossignol, with his son, Bonaventure, quickly came to the attention of Louis XIII's chief minister, Cardinal Richelieu, who found secure ciphers and codes of immense value to his diplomatic and intelligence corps.

As chief cryptographers, the Rossignols improved the impenetrability of the nomenclators (cipher tables) used by the French court. Antoine used out-of-order correspondences that required two tables organized to make finding the first element easy, without reference to the order of the second. Under Louis XIV, the Rossignols developed the Great Cipher and ran the Cabinet noir (Black Chamber), where intercepted letters were reviewed before being forwarded to their recipients.

Bonaventure's son, Antoine-Bonaventure, carried on the family’s trade until his death, whereupon the Great Cipher fell out of use and its key was lost. The cipher remained uncrackable for two centuries, leaving historians unable to read the coded diplomatic records from that era. It wasn’t until around 1893 that Étienne Bazeries, a French military cryptanalyst, finally deciphered it.

Today, we have sophisticated ciphers, algorithms and technology at our disposal, but these tools can only succeed in staying ahead of threats when combined with our ability to continually innovate. Louis XIV discovered that intelligence, or the “quill,” is Mightier than the Sword, and protects against threats and attacks–that’s certainly true today in terms of code making and breaking. This same spirit embraces our community as we come together each year to share knowledge, learn from each other and pass best practices from one generation to the next.