So, in 1993, in what was probably the first salvo of the first Crypto War, there was concern coming from the National Security Agency and the FBI that encryption would soon be incorporated into lots of communications devices, and that that would cause wiretaps to go dark. There was not that much commercial use of encryption at that point. Encryption, particularly for communications traffic, was mostly something done by the government.

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.

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.

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.

We basically have only two real tried and true techniques that can help counter this. One of them is to make systems as simple as we can, and there are limits to that because we can only simplify things so much. The other is the use of encryption.

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.

On balance, the use of encryption, just like the use of good locks on doors, has the net effect of preventing a lot more crime than it might assist.