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.

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.

In order for any smartphone manufacturer to decrypt the data on your phone, it has to hold onto a secret that lets it get that access. And that secret or that database of secrets becomes an extremely valuable and useful target for intelligence agencies.

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.

When the September 11th attacks happened, only about a year later, the crypto community was holding its breath because here was a time when we just had an absolutely horrific terrorist attack on U.S. soil, and if the NSA and the FBI were unhappy with anything, Congress was ready to pass any law they wanted. The PATRIOT Act got pushed through very, very quickly with bipartisan support and very, very little debate, yet it didn't include anything about encryption.

The security of computers and the Internet is a horrible and dangerous mess. Every week we hear about breaches of databases of Social Security numbers and financial information and health records, and about critical infrastructure being insecure.

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?