OABS: Efficient Outsourced Attribute-Based Signature Scheme With Constant Size

Attribute-based signature (ABS) extends the identity-based signature, in which the unique identity for the signer is expanded into an attribute set composed of multiple attributes. The current ABS schemes supporting linear secret-sharing scheme (LSSS) matrix are flexible, but the computational cost of the signing algorithm is linear with the number of required attributes. Therefore, it is inappropriate to constrained devices (mobile phone, tablet, etc.) which have limited computation power. For the sake of solving the above issue, we devise an key-policy outsourced ABS (OABS) scheme supporting LSSS access structure. The designed scheme provides the outsourced key for the cloud service provider (CSP) which computes most of module exponentiation in the signing phase. The signer only needs to perform lightweight calculations to endorse a message. The presented OABS scheme is proved secure against the q-Diffie-Hellman exponentiation (q-DHE) assumption under the standard model. In addition, the devised OABS scheme fulfills the signer privacy. Moreover, the signature length for the designed scheme is invariable and unrelated to the number of required attributes, which reduces communication cost. Performance analysis demonstrates that the designed OABS scheme is more high efficiency in the aspect of the computational cost.