Traceable policy-based signatures and instantiation from lattices

Policy-based signatures (PBS) were proposed by Bellare and Fuchsbauer (PKC 2014) to allow an authorized member of an organization to sign a message on behalf of the organization. The user’s authorization is determined by a policy managed by the organization’s trusted authority, while the signature preserves the privacy of the organization’s policy. Signing keys in PBS do not include user identity information and thus can be passed to others, violating the intention of employing PBS to restrict users’ signing capability.