There's no GUI PGP program for Unity/Gnome ever since they got rid of the text encryption plugin for Gedit. You can either install Kgpg (and like a hundred dependencies along with it), or learn command line GPG. If you're on 32 bit Linux, you can use GPG4USB (check the link in my signature), but it doesn't work on 64 bit Linux without, once again, installing a crap ton of dependencies, namely the ia32-libs.