Yeah man, you could make this font easily… after a little googling I found Times New Rot13: http://scruss.com/blog/2012/08/24/times-new-rot13-and-times-new-caesar/
In any font editing/creation program you just assign whatever glyph/shape to the associated field for that letter and you’re ready to go. Would be quite difficult to quickly decode because if you tried to copy+paste it the system would be seeing different letters to your visual perception. You’d have to OCR and then decode.
PS another one using DejaVu Serif and Sans http://eligrey.com/blog/post/rot13-dejavu-fonts/
