Cryptology ePrint Archive: Report 2008/097

Fairness with an Honest Minority and a Rational Majority

Shien Jin Ong and David Parkes and Alon Rosen and Salil Vadhan

Abstract: We provide a simple protocol for secret reconstruction in any threshold secret sharing scheme, and prove that it is fair when executed with many rational parties together with a small minority of honest parties. That is, all parties will learn the secret with high probability when the honest parties follow the protocol and the rational parties act in their own self-interest (as captured by the notion of a Bayesian subgame perfect equilibrium). The protocol only requires a standard (synchronous) broadcast channel, and tolerates fail-stop deviations (i.e. early stopping, but not incorrectly computed messages).

Previous protocols for this problem in the cryptographic or economic models have either required an honest majority, used strong communication channels that enable simultaneous exchange of information, or settled for approximate notions of security/equilibria.

Category / Keywords: game theory, fairness, secret sharing

Date: received 3 Mar 2008, last revised 4 Mar 2008

Contact author: alon rosen at idc ac il

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Version: 20080310:144304 (All versions of this report)

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