6. The Skill of Cybersecurity: Adversarial Thinking 139 where analytical game theory fails to provide a helpful analysis. For decades researchers have done experiments to observe what real people actually do when faced with strategic scenarios. This approach was initially called experimental game theory, but it eventually became known as behavioral game theory. It does not supplant traditional, analytical game theory, but it proves that there is an alternative that is more helpful in some contexts. Table 6.5 provides a summary comparison between analytical game theory and behavioral game theory. Table 6.5 A comparison of analytical and behavioral game theory. One of behavioral game theory’s major contributions is the concept of level-k reasoning. Level-k reasoning is the process of iteratively thinking about what the other player might do and how to best respond. Through many experiments it is well established that most people engage in some degree of level-k reasoning when faced with making a strategic decision. In level-k reasoning, the most obvious, instinctive strategy is the level-0 choice. Expecting your opponent to choose the most obvious strategy is the level-1 choice. Expecting your opponent to expect you to choose the most obvious strategy is the level-2 choice, and so on—the levels go on ad infinitum. The level-k type implicitly assumes his opponent is a level-(k - 1) type. In the traveling hacker’s dilemma, Veryl was using level-k reasoning when he thought that Ruth Ann may submit $500 (level-0) so he should submit $499 (level-1). But then it occurred to him Ruth Ann may anticipate him doing that and submit $498 (level-2), so Veryl should submit $497 (level-3), etc. A more familiar game that illustrates level-k reasoning is the rock paper scissors hand game. In this game two players simultaneously choose either rock, paper, or scissors. Rock is the level-0 choice because it is the first word in the name of the game and the players’ hands are in the rock position as they count down to the draw. Paper is the level-1 choice because paper beats rock, and scissors is the level-2 choice because scissors beats paper. Since there are only three choices, the level-3 choice circles back to rock and so on. A humorous illustration of level-k reasoning is portrayed in the film The Princess Bride. In the battle of wits scene, the man in black faces off against the evil genius, Vizzini. Vizzini must decide which of two cups is poisoned, and
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