From the BBC: The secret code of diaries.
The 300,000-word journal of Charles Wesley, the co-founder of the Methodist movement, which was written in an obscure shorthand, has been solved and the diary transcribed. It has taken nine years.
It appears that the shorthand was used not for speed, but for security. What was so important that it required the secrecy of a complex code?
(They tell you later on in the article.)
Wesley’s is not the only diary that has used a code, however, with everyone from Beatrix Potter to British prisoners of war using their secret diaries to express feelings that no-one else was meant to understand. [continue]
This kind of stuff fascinates me, partly because I’ve thought up a secret code system of my own, which I think would be awfully difficult for somebody to decode. Maybe one day I’ll develop it.
Assuming, of course, that you know the language used by the writer.
There are really only a handful of techniques for encryption that can be done by hand. Substitution cyphers and swapping cyphers are two of the more common ones. With a good enough computer, it’s possible to just brute-force the solution.