Societies without a reservoir of people who don't follow the rules lack an important mechanism for societal evolution. Vibrant societies need a dishonest minority; if society makes its dishonest minority too small, it stifles dissent as well as common crime.

Air travel survived decades of terrorism, including attacks which resulted in the deaths of everyone on the plane. It survived 9/11. It'll survive the next successful attack. The only real worry is that we'll scare ourselves into making air travel so onerous that we won't fly anymore.

History has taught us: never underestimate the amount of money, time, and effort someone will expend to thwart a security system. It's always better to assume the worst. Assume your adversaries are better than they are. Assume science and technology will soon be able to do things they cannot yet. Give yourself a margin for error. Give yourself more security than you need today. When the unexpected happens, you'll be glad you did.

Secret courts making secret rulings on secret laws, and companies flagrantly lying to consumers about the insecurity of their products and services, undermine the very foundations of our society.

I tell people: if it's in the news, don't worry about it, because by definition, news is something that almost never happens.

It is insufficient to protect ourselves with laws; we need to protect ourselves with mathematics.

The mantra of any good security engineer is: "Security is a not a product, but a process." It's more than designing strong cryptography into a system; it's designing the entire system such that all security measures, including cryptography, work together.