Rational Secret Sharing Information -- Theoretically Secure against Adaptive Adversaries

Most rational secret sharing protocols aim to achieve a more appealing equilibrium or resist adversaries. However, all previous protocols achieve resilience against irrational adversaries at the cost of inducing a weak guarantee of Nash equilibrium surviving iterated deletion, which has been proved weaker than strict Nash equilibrium. Moreover, they achieve equilibrium in a computational way based on the computational limitations of adversaries. In this paper, we design two unconditionally secure rational (t, n) secret sharing protocols. Contrary to prior works, our protocols induce an enhanced notion of strict equilibrium with respect to adversary structure A, and resist the computationally unbounded and adaptive adversary without using cryptographic primitives. Our protocols achieve stronger stability, since rational players have an incentive not to deviate no matter how the adversary behaves, and they are immune to the backward induction. Our protocols are secure against the adversary corrupting less than [n/3] players and the adversary corrupting less than [n/2]-1 players respectively. Both of them achieve utility independence.