Provably Secure Policy-Based Cryptography

The concept of policy-based cryptography (PBC) is a promising paradigm for trust establishment and authorization in large-scale open environments. A policy-based encryption scheme (PBE) allows to encrypt a message according to a policy so that only entities fulfilling the policy are able to perform the decryption of the message. Symmetrically, a policy-based signature scheme (PBS) assures that only entities fulfilling a given policy are able to generate a valid signature according to the policy. Existing PBC schemes suffer from either inefficiency or lack of strong security arguments. In this paper, we introduce policy-oriented strong security models for PBE and PBS schemes. Then, we present concrete and elegant PBE and PBS schemes from bilinear pairings. Our schemes are not only at least as efficient as existing schemes, but also, and more importantly, provably secure under the defined security models. keywords: Access Structures, Authorization, Trust Establishment, Bilinear Pairings, Provable Security