More on Code Breaking

Following the surprising amount of interest in my recent code-breaking activity publicised by the BBC and the Daily Telegraph, here is a little background.

Some years ago I was invited to take part in a historical event held at Mont Orgueil Castle in Jersey. My character for the week was to be the spymaster Philippe d’Auvergne. I was provided with a small look-out post at the top of the tower and a telescope. The weather was not the best and I decided to restrict my outdoor forays to a minimum, and prepared instead to display period code-breaking activities based on the story of George Scovell, who cracked the code used by Napoleon’s armies in Spain and Portugal during the Peninsular War.  For the benefit of visiting youngsters a set of simple cyphers was prepared for them to try their skill.

First I needed some coded documents. I wrote a computer program that would mimic the French coding system. The basis of the coding was that a single letter could be represented by up to half a dozen numbers of one, two or three digits. A number could also represent an entire word or group of commonly used letters forming part of a word.

I found some historical reports from the period in French and fed them into the program without reading them first. All I knew was the subject matter of the reports. I armed myself with pens, pencils, a notebook and an original 1791 French/English dictionary, as seen here:

Code breaker

Over the course of four days I managed to decode and translate one long document of about two pages and parts of several shorter ones that I used as cross-references. Sadly I have not been able to find any of the documents, but here from my notebook is a sample of my working:

My code-breaking notebook
The right hand page records the deciphered numbers, while the left hand page contains all the relevant notes.

I found this a most satisfying exercise, and I have recently used the same coding in my Peninsular War wargame campaign where the players requested messages to be in code.