I'm not sure this is appropriate to put here, since it has nothing to do with gamemaking, but a couple of you expressed interest in it when I mentioned it in chat, so I guess I'll put it here.
I wrote a very simple cryptography program in C. It passes over a file 4 times with 4 variants of Vigenere substitution-based encryption routines. It's nothing compared to PGP, TrueCrypt, or anything along those lines, but it's good enough to protect your data against all but the most determined of "enemies" when used properly.*
This download contains the executable, the C source code, and a test file. Please have a look and tell me what you think.
*I wouldn't bet too much on it.