A few days ago I saw a friend’s message on the Internet. The message looked like a bunch of random characters. Of course, I suspected a simple substitution cipher. What do I do? I copy the message to Emacs and run M-x rot13-region on it. (There are a few more rot13-related commands in Emacs, too.)
Alas, this didn’t help. It turned out that the friend used something else. Well, I hoped that giving a numeric prefix argument to rot13-region would work, but it didn’t.
This is Emacs, though, so it turned out that there is another function which can rot13-encode the region, but accepts a prefix argument and uses then a general Caesar cipher to encode it. The command is called message-caesar-region.
You’re welcome. 