The police break down your door and hustle you downtown for interrogation. Seems you’ve been using illicit cryptography to exchange information about—well, they’re not exactly sure, because you used cryptography, but they know it must be sinister because you used cryptography. And they know who you were talking to; their packet sniffers (and subpoenaed router logs) revealed that you were communicating with your friend a few miles away. They’ve arrested him too.
You’re going to jail. The question is, for how long?
The police don’t have enough evidence to convict you of the new crime, Encoding In The First Degree, carrying a penalty of five years in jail. But they can convict you of Second Degree Encoding, and that’s two long years in the overcrowded Minimum Security Federal Penitentiary for Computer Abusers.
They offer you a deal: if you agree to confess, and testify against your friend, they’ll let you go free. They offer your friend the same deal. But if you both decide to testify against one another, you each get four years in jail. You must both decide what to do in solitude, without communicating. (That’s why they split you up.)
You can either Testify (T) or Hold Out (H), and your friend can do the same. The outcomes are shown in the payoff matrix depicted in Figure 28-1.
Figure 28-1. Payoff matrix for a Prisoner’s Dilemma
What should you ...