The thing is, you can't design a web based system where you can't read the plaintext. If you have to give up your SSL key all bets are off. The FBI can perform

The thing is, you can't design a web based system where you can't read the plaintext. If you have to give up your SSL key all bets are off. The FBI can perform a MITM attack to your users. The best you can do in that case is shut down the service, which is what they did.