Security as a classification problem

(video, via)

Security requires that one can tell the bad guys and the good guys¹ apart. Security is thus, at least in part, a classification problem. Different approaches to security use different typs of classifiers. The Israeli profiling described in the video above essentially implements one particular decision tree. There is nothing particularly good or bad about this particular tree compared to others, or to entirely different ways of doing the job. What matters in the first place is that the classifier is either correct—it never confuses good and bad—or that it is at least biased in the right direction—it may misclassify good guys as bad guys², but not bad guys as good guys. A secondary consideration is efficency. The Isreali approach to airport security optimizes efficiency for a particular threat model.

¹ Or other entities. Security classification may work on objects, actions, situations, or really any combination of features that might matter.

² Assuming the enforcement stage of the mechanism does not cause permanent damage to entities classified as bad.