An Identity Escrow Scheme with Appointed Verifiers

An identity escrow scheme allows a member of a group to prove membership in this group without revealing any extra information. At the same time, in case of abuse, his identity can still be discovered. Such a scheme allows anonymous access control. In this paper, we put forward the notion of an identity escrow scheme with appointed verifiers. Such a scheme allows the user to only convince an appointed verifier (or several appointed verifiers) of his membership; but no unauthorized verifier can verify a user’s group membership even if the user fully cooperates, unless the user is completely under his control. We provide a formal definition of this new notion and give an efficient construction of an identity escrow scheme with appointed verifiers provably secure under common number-theoretic assumptions in the public-key model.