I was doing some research for S/MIME and created my own personal S/MIME certificate using Comodo’s Free S/MIME certificate authority. I was wondering if I should try doing this for GMail, but as I use gmail mainly for web registrations, I decided not to do so. Article in the link describes how to do it even if you only have a web interface and are using Firefox.
Anyways, I was thinking about adding encryption support to Kyberia portal and how would I do it, so that’s the reason I researched it. Using newly proposed HTML 5 local storage, you could store keys locally. While this would probably be the most secure way of doing it, it also requires, that the keys would be stored in each user’s browser (so using different browser for viewing the data is not possible).