Ive not read the rest of the comments yet but it seems to me that there isnt a way to enforce this.
You can compel companies to give you access to their services but anyone wanting to communicate privately will find ways to do so.
I mean whats to stop me going on twitter and tweeting a lump of 140 characters of encrypted text with a #TodaysBigNewsStory hash tag?
Potentially thousands will see it and disregard it - only the one guy that I have previously shared the key with can decrypt it...
Actually Im pretty sure I could patent this in the US :)
Or you know.. we could go back to the 70s and start posting hidden messages in the lonely hearts section of the local paper..