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.
Keywords Identity escrow - group signatures - privacy protection - formal model for group signatures