Constant Size Ciphertext Distributed CP-ABE Scheme With Privacy Protection and Fully Hiding Access Structure.

In ciphertext-policy attribute-based encryption (CP-ABE) schemes, the computational over-head and the length for the ciphertext are positively correlated with the complexity of the access structure. In addition, the access structure embedded in ciphertext may be a leak sensitive information for the user. In order to solve the above issues, we provide a constant size ciphertext distributed CP-ABE scheme with privacy protection and fully hiding access policy (PPFH-CP-ABE) scheme. Our scheme can protect user's privacy from the following two aspects: 1) A user obtains private keys for his attributes from different authorities who get nothing about user's global identifier (GID) and attributes and 2) Access structure in the ciphertext is fully hidden. In addition, our scheme is able to resist the collusion attacks since the user's GID is nonlinearly bound to his private key from each authority. The presented scheme is proven CPA-secure in selective security model under the decisional DBDH assumption.