When I searched for use of the term "système à double clef" in studying popularization of the Vigenere cipher (see here), I came across a description (Auguste Héraud) that the double-key cipher like Vigenere was used by Napoleon when he returned from the island of Elba. Googling readily found publications containing the actual ciphertext, which showed Héraud's description is inaccurate.
I uploaded a new article "Enciphered Proclamation to the Army Attributed to Napoleon in Elba", which presents the cipher and some background information. Help of historians and cryptographers is desired to assess its authenticity.
I also added a reference to this in "Great Ciphers of Napoleon's Grande Armée"
The overall story seems true. I added additional notes on this.
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