What encryption lets us do is say, "Yes, the Internet is insecure." Bad guys are able to compromise computers everywhere, but we're able to tolerate that because if they do intercept our messages, they can't do any harm with it.

As we build systems that are more and more complex, we make more and more subtle but very high-impact mistakes. As we use computers for more things and as we build more complex systems, this problem of unreliability and insecurity is actually getting worse, with no real sign of abating anytime soon.

Clipper took a relatively simple problem, encryption between two phones, and turned it into a much more complex problem, encryption between two phones but that can be decrypted by the government under certain conditions and, by making the problem that complicated, that made it very easy for subtle flaws to slip by unnoticed. I think it demonstrated that this problem is not just a tough public policy problem, but it's also a tough technical problem.

The perspective that law enforcement is presenting seems to be a very narrow one that's focused very, very heavily on investigations of past crimes rather than on preventing future crimes. It's very important for policymakers to take that broader view because they're the ones who are trusted to look at the big picture.

If it were possible to hold onto this sort of database and really be assured that only good guys get access to it, we might have a different discussion. Unfortunately, we don't know how to build systems that work that way. We don't know how to do this without creating a big target and a big vulnerability.

It may be true that encryption makes certain investigations of crime more difficult. It can close down certain investigative techniques or make it harder to get access to certain kinds of electronic evidence. But it also prevents crime by making our computers, our infrastructure, our medical records, our financial records, more robust against criminals. It prevents crime.

From a policymaker's point of view, [the back door] must look like a perfect solution. "We'll hold onto a separate copy of the keys, and we'll try to keep them really, really safe so that only in an emergency and if it's authorized by a court will we bring out those keys and use them." And, from a policy point of view, when you describe it that way, who could be against that?