I believed then, and continue to believe now, that the benefits to our security and freedom of widely available cryptography far, far outweigh the inevitable damage that comes from its use by criminals and terrorists. I believed, and continue to believe, that the arguments against widely available cryptography, while certainly advanced by people of good will, did not hold up against the cold light of reason and were inconsistent with the most basic American values.

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.

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.

Computer science doesn't know how to build complex systems that work reliably. This has been a well-understood problem since the very beginning of programmable computers.

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?

As the local police department might want to decrypt a phone of a criminal suspect, so would the Chinese or the Russian or the Iranian intelligence agencies like to be able to do exactly the same thing.

There's been a certain amount of opportunism in the wake of the Paris attacks in 2015, when there was almost a reflexive assumption that, "Oh, if only we didn't have strong encryption out there, these attacks could have been prevented." But, as more evidence has come out - and we don't know all the facts yet - we're seeing very little to support the idea that the Paris attackers were making any kind of use of encryption.