Dropbox has its demons, however, and it's probably not something you should rely on for its security. I used to use it as a means of keeping an encrypted file

Dropbox has its demons, however, and it's probably not something you should rely on for its security. I used to use it as a means of keeping an encrypted file synced across machines, but when you re-lock up the file it... well, encrypts it, which means re-arranging ALL the bits, so a diff (how dropbox syncs) is just the whole damn file.