The codebook from 1691 broken by Bazeries () ()

My Web page about Cryptology

The Louis XIV's codebooks

  • Introduction (introduction)
  • The invention of the great chipher (invention)
  • Analyse of Louis XIV's codebooks (analyse)
  • Cryptanalyse (break)
  • Codebooks examples (examples)
    • A codebook from 1643
    • A one part codebook from 1676
    • A two part codebook from 1676 (the first one?)
    • A one part codebook from 1684
    • Messages encoded by a two part codebook from 1685
    • A two part codebook from 1688
    • Messages from 1690, an unpublished codebook?
    • The codebook from 1691 broken by Bazeries
    • A codebook from 1701
  • The Man in the Iron Mask (mask)

Introduction

In 1891, Commandant Gendron, of the general staff of the army, made a study on the campaigns of Catinat. He found himself stopped in his research by ciphered messages. These despatches dealt with the French invasion in the Dauphiné within the more general framework of the War of the League of Augsburg. He communicated them to Commander Bazeries, who after examination, made a point of deciphering them. …

Bazeries succeeded in this tour de force (see the deciphering of Bazeries). Bazeries thought he was the first to break a double table code, I think he was wrong (see the English decipherments).

The encrypted letters used by Bazeries to break the 1691 code

Here are those letters. The reader can "from scratch" try to decipher them. He can also use a small "Rosetta stone" which is made up of a small partial decryption.

Here the codebook:

As we can see, it is a code with double tables of 587 groups.

In the previous chapter I indicated that in the memoirs of Catinat there are other letters, dating from 1690, encrypted by the same code as that reconstituted by Bazeries (cf. code of 1690).

Erroneously, Bazeries deduces from the missives from 1691 that the iron mask was none other than Monsieur de Bulonde (cf. the Man in the iron mask). He was so impressed by his discovery that he published a book which mainly deals with this theory concerning the supposed true identity of the iron mask.

Small and large number

Here is a new excerpt from the book "Le masque de fer":

The codebooks in use (in the time of Louis XIV) were always two in number: the Great and the Small.

The Great cipher was reserved for the correspondence of the sovereign and the ministers with the commanders-in-chief of the armies.

The small cipher, used concurrently with the large one, was specially assigned to the correspondence with governors, intendants, place commanders, etc. ; it differed from the large one only by its lower number of groups (1)

(1) The dispatch from Feuquières to Catinat of January 25, 1691, relating to Veillane, was composed with the small number. The deciphering of this dispatch by Major Bazeries at the same time made it possible to note that the small cipher of 1691 included only 367 groups while the large one used 587.

The letter from Feuquières to Catinat of January 25, 1691 (Encrypted letter).

References

  • Le masque de Fer, Révélation de la correspondance chiffrée de Louis XIV. Emile Burgaud et commandant Bazeries, 1893, librairie de Fimin-Didot.
  • Savoyard–Waldensian wars (Wikipedia)