Group DMs

perhaps a room_key could be generated automatically by sha2(creator_sec_key+room_id). then the creator could invite people without needing to swap passwords?` to join you just need the room_id + room_key. seems simple enough... you could deliver a room invite (room_key and room_id) over an encrypted DM. this means anyone in the group could invite as well since they all have the room_key. just what I got off the top of my head.