International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Sequential Rationality in Cryptographic Protocols

Ronen Gradwohl
Noam Livne
Alon Rosen
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Abstract: Much of the literature on rational cryptography focuses on analyzing the strategic properties of cryptographic protocols. However, due to the presence of computationally-bounded players and the asymptotic nature of cryptographic security, a definition of sequential rationality for this setting has thus far eluded researchers. We propose a new framework for overcoming these obstacles, and provide the first definitions of computational solution concepts that guarantee sequential rationality. We argue that natural computational variants of subgame perfection are too strong for cryptographic protocols. As an alternative, we introduce a weakening called threat free Nash equilibrium that is more permissive but still eliminates the undesirable ``empty threats'' of non-sequential solution concepts. To demonstrate the applicability of our framework, we revisit the problem of implementing a mediator for correlated equilibria (Dodis Halevi-Rabin, Crypto'00), and propose a variant of their protocol that is sequentially rational for a non-trivial class of correlated equilibria. Our treatment provides a better understanding of the conditions under which mediators in a correlated equilibrium can be replaced by a stable protocol.
  title={Sequential Rationality in Cryptographic Protocols},
  booktitle={IACR Eprint archive},
  keywords={foundations /},
  note={ 14839 received 18 Aug 2010},
  author={Ronen Gradwohl and Noam Livne and Alon Rosen},