Among some of our engineering colleagues, "theory" has a bad reputation, seeming to have connotations of "impractical" and "divorced from reality." This reputation is unfortunate, particularly in computer science. Computation itself is an abstract, mathematical concept. The rigor of mathematics lets us talk precisely about it. In this sense, "theoretical" computer science can lead us toward, rather than away from, the heart of what's really going on here.
The tools of theoretical computer science help illuminate many aspects of the security craft. In this appendix, we provide deeper discussion of some of the topics in this space, broached briefly earlier in the book.