PHAS-HEKR-CP-ABE: partially policy-hidden CP-ABE with highly efficient key revocation in cloud data sharing system

In recent years, attribute-based encryption (ABE) provides a new idea to help researchers solving the problem of data privacy protection in cloud. But there are two issues in traditional ABE, the first issue is that the attributes in the access structures will be sent to users in cleartext together with the ciphertext. So a attacker has the opportunity to obtain some of the private information from the plaintext access structure. And the other issue is the traditional ABE scheme cannot revoke the users' illegal keys in an efficient way. To handle both of the above challenges, we come up with a large universe ciphertext-policy ABE (CP-ABE) scheme which supports partially hidden access structures (PHAS) and highly efficient key revocation at the same time in this paper. What's more, unlike most previous schemes, first our access structure is based on the expressive linear secret sharing scheme (LSSS) which supports both AND and OR gates in access formulas and second our scheme is built from the prime-order bilinear pairing groups. The comparison with other relevant works presents that our scheme is more comprehensive and efficient. Finally we rigorously prove and analyze that our scheme is selectively indistinguishable secure under chosen plaintext attacks (IND-CPA) in the random oracle model (ROM) and our access structure is really anonymous against off-line dictionary attacks.