That's where the nice chaps over at the Seahorse project come in - they've developed a handy utility to stop me from giving away national secrets. It even lets you encrypt the contents of your clipboard!
This feature is probably the most useful if you have to send some confidential text over IM or similar. To use clipboard encryption, right-click an empty space on one of your panels, select Add to Panel... and then drag the Clipboard Text Encryption item to somewhere on a panel.
I'm probably ripping you off here - I can't remember this feature being in Edgy, but the package release logs seem to suggest otherwise, so it might not actually be new for Feisty. Can you ever forgive me?