Efficient and Provable Secure Ciphertext-Policy Attribute-Based Encryption Schemes

In a ciphertext-policy attribute-based encryption (CP-ABE) scheme, the data is encrypted under an access policy defined by a user who encrypts the data and a user secret key is associated with a set of attributes which identify the user. A user can decrypt the ciphertext if and only if his attributes satisfy the access policy. In CP-ABE, since the user enforces the access policy at the encryption phase, the policy moves with the encrypted data. This is important for data storage servers where data confidentiality must be preserved even if the server is compromised or un-trusted. In this paper, we provide an efficient CP-ABE scheme which can express any access policy represented by a formula involving $\wedge$ and $\vee$ boolean operators. The scheme is secure under Decision Bilinear Diffie-Hellman assumption (DBDH). Furthermore, we extend the expressivity of the scheme by including \emph{of} (threshold) operator in addition to $\wedge$ and $\vee$ operators. We provide a comparison with existing CP-ABE schemes and show that our schemes are more efficient. Especially, the computational work done by the decryptor is reduced.