Privacy-Preserving Attribute-Based Encryption Supporting Expressive Access Structures

As a promising cryptographic primitive, attribute-based encryption (ABE) is adopted to protect outsourced data. However, there are some issues in existing attribute-based encryption schemes. First, the attribute authority manages attributes of users, so it may cause the leakage of users' privacy information. Second, because the access structures are directed along with the ciphertexts and may violate the privacy of ciphertexts, it is desirable to hide the access structures information. Another thing is that expressive access structures are important for the sake of practicality. In this paper, to simultaneously obtain privacy protection and desirable expressiveness, a privacy preserving attribute-based encryption scheme supporting expressive access structures is proposed. The proposed scheme, not only protects users' attribute information and hides expressive access structures, but it also outsources most of the decryption calculations to the cloud server. The proposed scheme is proven secure against chosen-ciphertexts attacks under the Decisional Diffie-Hellman (DDH) assumption.