Renegotiation-Safe Protocols.
Rafael Pass, Abhi A. Shelat · 2011
We consider a model of renegotiation in extensive-form games: when it is player i’s turn to move, i can “renegotiate ” the equilibrium by suggesting new strategies for all players for the remainder of the game. This renegotiation is successful if it improves i’s utility, and cannot itself be renegotiated at a later round in the game. Although not all finite games have renegotiation-safe strategies, natural classes of games do. We argue that renegotiation-safety captures rationality in the context of cryptographic protocols in a more meaningful way than traditional solution concepts. We also present protocols for the task of secret sharing that are renegotiation-safe assuming the existence of two non-negotiating players; additionally, we show that such protocols require the existence of at least one non-negotiating player.