Main point - I'd be willing to bet that the NSA collects as many private keys as it can. Can't prove it, don't need to. I'll conduct myself as if they have all the private keys. That's a loss of freedom, and that's not what the authors of the fourth amendment intended.
Some percentage. It's also been reported that one tactic used by terrorists or suspected terrorists was to share a login to an email account - editing unsent messages that live on the email provider's servers in draft mode. Email monitoring won't catch those.
The same technique used by former CIA Director David Petraeus and Paula Broadwell to communicate.
Main point - I'd be willing to bet that the NSA collects as many private keys as it can. Can't prove it, don't need to. I'll conduct myself as if they have all the private keys. That's a loss of freedom, and that's not what the authors of the fourth amendment intended.