A Specimen of Napoleon's Small Cipher (1813)

Bazeries' Les chiffres secrets dévoilés presents a partially reconstructed small cipher used by Napoleon's generals in 1813, which underwent no change during the whole campaign. It had entries ranging from "1 cinq" to "182 es" (p.275) (pdf of the reconstruction is found here). He also presents a partially encoded text of a letter of 6 November 1813 (p.169-181) from General Rapp (Wikipedia), who defended Danzig against the allied forces. Danzig was to surrender on 17 November 1813. (The reconstruction was independently achieved by J. Vilcoq, who reproduced the first and the last pages of this despatch in "Le Chiffre sous le Premier Empire", Revue Historique de L'Armee No.4 (1969).)

One characteristic of this code is that the same code number may represent not only several variants of a word but also its truncated forms. For example, Bazeries' reconstruction has an entry "39 al.lemagne.and.s.es", meaning that "39" may represent "al" as well as variants such as "allemagne", "allemand", "allemands", "allemandes".

In the above example letter, of which the beginning paragraphs are quoted below, "52" is used both as "de" and "defense" and "145" is used both as "ti" and "tion."

Such multivalency was employed in French codes as early as in Louis XIV's age (see another article). John Wallis, an English mathematician, who deciphered French ciphers at the time, observed that such "imperfection" might be indicated by a line placed below a figure but such marking was occasionally neglected. The text of Bazeries does not show any such markings.

J'envoye pres de Votre Majeste un de mes aides de camp pour lui rendre compte 52<de> 106<la> 167<s> 119 150<tu> 15<a> 145<tion> 52<de> 166<la> 137 106<la> 20<ce> de 12<Danzig> 46<Un> 107<ma> 96<l> 61<he> 138 169<r> 119 169<r> 126<re> 156<pa> 146<ra> 37 117<le> 82<es> 176<t> 22<ar> 148<ri> 132<ve> 119 6<c> 119 dans la 104<nu> 119 176<t> 76<du> 137 126<re> 95<mi> 62<er> 15<a> 138 52<de> 138 151<x> de ce 111<mo> 119 167<s> 117<le> 58<feu> 15<a> 6<c> 149<on> 174<su> 99<me> 117<le> 167<s> 45<car --> quar> 145<ti> 53<e> 169<r> 167<s> de 121<no> 167<s> 19 137 137 159<ro> 161<vi> 167<s> 119 90<o> 94<ne> 99<me> 115<n> 167<s> 50<et> 134<si> les 22<ar> 114<m> 53<e> 167<s> de V.M. 94<ne> 106<la> 99<me> 176<t> 176<t> 68<en> 176<t> 68<en> 50<et> 34<at> 52<de> 69<fa> 119 126<re> 37 119 68<en> 157<to> 176<t> 117<le> 132<ve> 169<r> 117<le> 167<s> 119 53<e> 60<ge> 106<la> 177<se> 138 117<le> 165<pe> 169<r> 167<s> 165<pe> 6<c> 145<ti> 132<ve> 52<de> 20<ce> 176<t> 176<t> 53<e> 78<place[?]> qui s'est 97<im> 111<mo> 169<r> 158<ta> 93<li> 177<se> 53<e> par 52<de> 110<lo> 115<n> 81<g> 167<s> et continuels 174<su> 6<c> 6<c> 53<e> 167<s> 82<es> 176<t> de 176<t> 62<er> 95<mi> 94<ne> 169<r> par la 4<ca> 137 145<ti> 161<vi> 131<te> 46<un> 53<e> 52<defense> 134<si> glorieuse.
119<J> 53<e> 119<j> 139<oi> 115<n> 167<s> 15<a> 20<ce> 146<ra> 137 137 90<o> 169<r> 176<t> les 53<e> 158<ta> 176<t> 167<s> de 134<si> 150<tu> 15<a> 145<tion> des 176<t> 159<ro> 138 137 137 53<e> 167<s> tant 9<ba> 142<y> 90<o> 115<n> 115<n> 53<e> 176<t> 176<t> 53<e> 167<s> que 107<ma> 106<la> 52<de> 167<s> et 6<c> 149<on> 170<va> 117<le> 167<s> 20<ce> 115<n> 176<t> 167<s> 117<le> 157<s> 53<e> 158<ta> 176<t> 167<s>