Extending the ciphertext-policy attribute based encryption scheme for supporting flexible access control

Ciphertext-Policy Attribute Based Encryption (CP-ABE) is recognized as an important data protection mechanism in cloud computing environment for its flexible, scalable and fine-grained access control features. For enhancing its security, efficiency and policy flexibility, researchers have proposed different schemes of CP-ABE which have different kinds of access policy structures. However, as far as we know, most of these structures only support AND, OR and threshold attribute operations. In order to achieve more effective data self-protection mechanisms in open environments such as Cloud computing, CP-ABE needs to support more flexible attribute based policies, most of which are described using operators of NOT, <, ≤, >, ≥. This paper proposed an Extended CP-ABE(ECP-ABE) scheme based on the existing CP-ABE scheme. The ECP-ABE scheme can express any access policy represented by arithmetic comparison and logical expressions that involve NOT, <, ≤, >, ≥ operators in addition to AND, OR and threshold operators. We prove the Chosen-plaintext Attack (CPA) security of our scheme under the Decisional Bilinear Diffie- Hellman (DBDH) assumption in the standard model, and also discuss the experimental results of the efficiency of ECP-ABE.