There is no need for that decryption to occur server-side.
How will they be distributed and replaced?
Who will generate them?
How will they get on my phone?
What happens when my phone is stolen?
How will they get to the people who want to communicate with me?
Hacking out a local client usable by unix nerds punts on these problems, more or less. Solve these problems in a way that fits into the workflow of present day average e-mail users (ie, my mom) and you will have something.