Messages encoded by a two part codebook from 1685 () ()

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  • Messages from 1690, an unpublished codebook?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)

A cipher letter from 1685

In Catinat's memoirs, a letter dated 1685 seems to be the oldest example of the use of a two part codebook.

Note: the date is not very legible, but taking into account the previous and following dated documents, the date 1685 seems to be the most likely. In any case, it is only the last digit that is suspect (the 5).

Here is the letter

Here is an exerpt:

Si vous jugez à propos de ne pas plus fatiguer
de garde la garnison de la ville que n'est celle
de la citadelle, le roi approuve que vous le
fassiez: mais il régler cela de manière qu'il
n'y aipas moins de quate cents soldats fran-
çais qui montent la garde à la ville, et les distri-

                 X    X    X  qu  o  u   i
buer de manière 401. 421. 218. 1. 6. 60. 57.
 l   y    a    u   ra   u    n  so   l    da   t
90. 124. 202. 69. 195. 134. 18. 70. 114. 356. 41.
 i   ta   li   e   n   i   l   y    e   n   a    i
112. 20. 132. 43. 22. 57. 90. 178. 43. 18. 202. 112.
 t   to   u    s   io   u  r   s   de  u    x
123. 84. 177. 16. 308. 60. 5. 59. 105.134. 127.
 f    ra   n   co   i    s   x    x
253. 317. 18. 148. 112. 68. 429. 186., et comme
présentement que vous devez être en possession
du château, les postes que vous teniez de ce ...

If you deem it advisable not to tire the garrison of the city more than that of the citadel, the king approves of your doing it: but he will regulate it in such a way that there are no less four hundred French soldiers who mount guard in the town, and distribute them in such a way that where there is an Italian soldier there will be two Frenchmen every day as a presentment that you must be in possession of the castle, the posts which you hold of this...

It should first be noted that only part of the letter is encrypted. At the time, it was a common practice although reducing security. Bazeries' assertion that Louis XIV's codes and their use were clearly superior to Napoleon's is arguably overstated.

Encrypted lines are overcome by their group-to-group translation. It was therefore easy for me to reconstruct the part of the code corresponding to the encrypted groups used. Nuls are represented in the translation by capitalized X letters.

The code used

a   202,162             i   57,112              r   5,31
c   231                 io  308                 ra  195,317,379
ca  179                 l   90,114              re  64,75,47,3
Casal   413             la  94                  s   16,59,68,168,204
ce  37                  le  78,325              sa  25
ci  223                 li  265,132             se  160
co  148,272             ma  146                 si  8
cu  382                 me  13,75               so  70
da  356                 M.Mantoue   431         su  225
de  105,120,29,82       mo  263                 t   41,123,99
du  105                 n   18,22,194,113,173   ta  20,23
e   43,164,111          ne  91,286              te  15,35,62
et  158                 ni  328                 ti  67,161
f   253                 o   6,32                to  84,171
fe  361                 p   10                  u   60,69,134,177
fi  29                  pe  53                  uo  71,46,73
fu  374                 qu  1                   x   107,185,127,76,401,
g   206                 que 27                  y   124,178

If we inspect the letter, we notice that the use of nulls makes it possible to hide the true beginning and the true end of the encrypted parts.

References

• Mémoires et correspondance du maréchal de Catinat, Tome II (1819) (Google)