I often find myself working on my laptop on the train, or in another public place. Sometimes I'd like to spend that time writing things that I'd prefer not to be read over my shoulder by random fellow travelers. It occurred to me that this goal could probably be attained with a utility that would rot13 all text on a tty (my laptop is text-mode-only due to being a 486 with 4Mb RAM :) ).

However, my searches for software to do this have come up empty so far. I'd even settle for a VIM mode that would accept keystrokes normally, but display everything rot13'd - everything I'm concerned about right now would be in VIM. Is it really true that nobody's come up with a "conceal what you're doing" rot13 program?