If you want privacy, stay off the Web.
Yeah, well we're at it why don't we get rid of this whole encryption thing? It seems a little difficult for most people to understand. Making people think of new solutions is obviously undesireable, so let's just not try.
If you want a solution to your problem, here it is: every message that starts with '/' will be sent off to a sub with a dispatch hash, it will then check the letters following / and if the first letters before the space aren't a valid command (such as 'msg') or doesn't contain the valid parameters (such as username for /msg) it will return an error to the user. So if someone tried to type '/mseg Ovid blah' they would get an error saying "you tried to type /mseg Ovid blah blah. Then since they're lazy, they can cut and paste and switch /mseg to /msg and resend.