Selfishness in P 2 P Networks 1 Introduction

Selfishness in P 2 P Networks 1

Introduction to Game Theory U C B E R K E L E Y C O M P U T E R S C I E N C E Prisoner Dilemma Two members A, B of a criminal gang are arrested and put in separate solitary confinement. The prosecutors lack sufficient evidence and hope to convict them of at least to a lesser charge to get both sentenced to one year in prison. But they offer each prisoner a bargain. Each prisoner is given the opportunity either to: betray the other, or confess the crime by remaining silent. The offer is: If A and B each betray the other, each serves 2 years in prison If A betrays but B confesses, then A will be free but B will get 5 years ( and vice versa) If A and B both confess, then both of them will only serve 1 year in prison 2

Prisoner’s dilemma U C B E R K E L E Y C O M P U T E R S C I E N C E What will A and B do? What is the lesson? 3

Prisoner’s dilemma U C B E R K E L E Y C O M P U T E R S C I E N C E Because betraying the fellow criminal offers a greater reward than cooperating (i. e. confessing), all purely rational self-interested prisoners will betray the other, and thus both Will get 5 years instead of 1 year. Selfishness is often considered rational, but there is a price. 4