Can you decipher a coded message written on the cover page of a letter dated 20 February 1818?

cryptology/coded.message.1818 New

New entry, edited from material collected for the archive and not yet in a released version.

Problem

Can you decipher a coded message written on the cover page of a letter
dated 20 February 1818?

The letter was from a French attorney to his English client, about the
disposal of property in France, so the coded message may refer to
business matters.  The letters have all been in English, but the
Englishman also read French, so the message may be in French.

[ Editor: the coded message itself was an image (message.jpg) on the
poser's web page, http://www.cart.demon.co.uk/puzzle.html, and is not in
the collected material. ]

-- Robey Callahan <rc@cart.demon.co.uk>, <shrba@csv.warwick.ac.uk>

Show solution

Many years ago--I don't remember where--I learned of something called a
tic-tac-toe cipher.  Your message seems to be an example of it.

The idea is that the key consists of the letters of the alphabet written
in a tic-tac-toe grid, three per box, thus:

 A B|D E|G H
  C | F | I
 ---+---+---
 J K|M N|P Q
  L | O | R
 ---+---+---
 S T|V W|Y Z
  U | X |

Each letter is represented in the message by the edges of its box,
accompanied by zero, one or two dots to indicate which of the three
letters is meant.  The placement of the dots is arbitrary; only their
number matters.

I don't remember what convention I originally saw for which numbers of
dots indicate which letters, but the scheme that seems to work for your
message is two dots for the first, one for the second, none for the
third.

The message then works out to this:

          maqy
          wine

you have throbt
notary qualhc

Somewhat encouraging, but doubtful.  If we allow for some inaccuracy in
the number of dots (btw, the jpeg is a scan of your transcription, not
the original, right?), we can make four changes to get all English
words:

          mary
          wine

you have throat
notary qualia

Gibberish to me, but perhaps you can make something of it in context.

-- Fred W. Helenius <fredh@ix.netcom.com>

Good eye!  I suggest "PUBLIC" rather than "QUALIA" for the last word.
It requires three changes rather than two, but (a) they're all in the
same boxes, and (b) it makes sense.  I don't have a good alternative for
"THROBT/THROAT", though.

-- Jim Gillogly <jim@acm.org>