Shoutbox

I've had an idea for a script, it's around encoding messages in order to unable sniffers or whatever other things like that to see messages, but whithout specific passwords, i'thought something about asymetric keys or something like that.

Do any of you have any ideas or comments about this?
What functions would you like this script to do?
Do you think this would be useful?

Simply tell me, and I'll try to do the better I can.
Thanks!