Applied Cryptography is both a great read and an invaluable handbook.

Beyond Fear should be required reading for anyone in the security industry.

Electronic security is a matter of math. Though electronic devices touch everyone’s life in modern society, not everyone is mathematical. Even professionals concerned with securing electronic systems are often insufficiently mathematical to directly experience the truth of a rigorous proof.

To bridge this gap, Schneier discusses how the math applies to the reality in terms that most people can grasp. He does not hesitate to give sources that peers can check, and publishes errata when warranted. I think this is why he has so many admirers and comparatively few critics, despite the controversial and contrarian viewpoints he puts forth.

Apropos a previous posting, I don’t know if Schneier should be the head of DHS —I have no idea if he’s a talented manager or executive—but he should definitely be the “CTO” of DHS if nothing else!