What are you exactly looking for? CryptKeeper seems like a cryptography software. Is it really what you're looking for?
If you simply want to prevent anyone from accessing your "folder" (not to sound pedantic, but on Unix you'd call it a directory), the easiest thing would be to change the permissions. I'm sure there's a way to do it graphically on Ubuntu (I don't know the new Ubuntu, but I'm guessing you'd have to right click on the directory and go to properties or something). On the command line though, you simply have to put:
chmod 700 <path_to_your_folder>
That way, the only user who'd have access to it would be you.
If you need more explaining don't hesitate to ask :)