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Antoine Rossignol

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Susanna: I hope for Pepys’ sake that his cipher was a good one, although I doubt it was as cleverly nasty as the Great Cipher used by Louis XIV’s spymasters, Antoine and Bonaventure Rossignol (father and son), which after their deaths (they had not passed its secrets on to anyone else) was not broken until the 1890s. (For more fascinating information about the history cryptography, I recommend “The Code Book: the Evolution of Secrecy from Mary Queen of Scots to Quantum Cryptography”, by Simon Singh.)

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Wikipedia: Rossignols

The Rossignols, a family of French cryptographers and cryptanalysts, included: * Antoine Rossignol (1590 - 1682) * Bonaventure Rossignol * Antoine-Bonaventure Rossignol

The family name meant "nightingale" in French. Since the 1700s, though, the word rossignol has served as the French term for "skeleton key" or for any tool which opens that which is locked: not because of birds, but because Antoine Rossignol became one of the great code and cipher experts, both for the making or the breaking of secret communications. His son and grandson continued his cipher-based work in service to the French crown.

In 1626, Henri II of Bourbon, Prince de Condé laid siege to the Huguenot city of Réalmont. The besiegers intercepted a coded letter leaving the city. Rossignol, then a 36-year-old mathematician, had a local reputation for his interests in cipher. He quickly broke the Huguenot cipher, revealing a plea for bringing ammunition through the blockade to replenish the city's almost exhausted supplies. The next day, the besiegers presented the clear text of the message to the commander of Réalmont, along with a demand for surrender: the Huguenots capitulated.

This brought Rossignol to the attention of the chief minister, Cardinal Richelieu, who found secure ciphers and codes of immense use to his diplomatic and intelligence corps. Rossignol repeated his swift decipherment of Huguenot messages at the siege of La Rochelle in 1628.

Rossignol improved the nomenclators (cipher tables) used by the French court for their own dispatches. A nomenclator comprises a hybrid of code and cipher. Notable important words go into code rather than getting spelled out, while the bulk of the message consists of simple cipher. Before, to make them compact, the alphabetical order of the clear words would correspond closely to the order of the code, so that the codes for the English words "Artois", "Bavaria", "cannon" and "castle", would appear in that order. Rossignol insisted on using out-of-order correspondences, necessitating the use of two tables, one for clear to code, the other for code to clear, organized to make finding the first element easy, without reference to the order of the second.

The Abbé de Boisrobert wrote a poem in praise of Rossignol, Epistres en Vers.

In the era of Louis XIV (reigned 1643 - 1715), Antoine Rossignol and his son, Bonaventure, worked either at their estate at Juvisy near Paris or in a room next to the King's study at Versailles. For him they developed the Great Cipher of Louis XIV. They alone mastered it, encoding letters, memoranda, and records. They ran for France the Cabinet Noir, the French Black Chamber (founded when Louvois served as Minister of War), so notable that "black chamber" became an international term for any code bureau.

A generation later, when Bonaventure's son, Antoine-Bonaventure, died, the Grand Cipher fell out of use. Absent the key, and even the base concept, it remained uncrackable until three years of work in the later 19th century by Etienne Bazeries. During this time, historians remained unable to read the coded diplomatic records of the time in the French archives.

Antoine Rossignol had the title of "King's counselor". Both Bonaventure and Antoine-Bonaventure Rossignol reached the position of "president of the Chamber of Accounts."

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