How to easily install any GPG GUI on Ubuntu that actually works?
Solution 1:
Besides Seahorse, which is only the key manager, you need a package called seahorse-nautilus to be able to encrypt/decrypt files with Nautilus.
It adds a menu item to the right-click context menu that allows you to encrypt a file directly from the file manager.
Note: This is the package name in Ubuntu 14.04. Other versions may have a different package name.
Additional Note: It may be required to log out of the current session and re-login for everything to work properly after installing the required packages.