The Craft of System Security

17. In Search of the Evil Bit

In Chapter 1, we introduced our favorite way of thinking about systems and security. At any given time, the state of the system is some particular element of the set States. We can partition this set into two subsets: Bad and NotBad. The goal of the adversary is to somehow get the system into a state in the Bad. The goal of the system defender is to keep that from happening. However, since we can't always meet our goals, we might settle instead for simply knowing whether the adversary has already achieved his or her goal. (This does not necessarily imply that the adversary has won—we could simply be trying to detect whether the adversary has achieved the first step of a longer-range attack.)

In many defense situations, ...