Access Control Over Secured Data in Public Cloud Server

Data access control has become a very challenging issue in public cloud storage systems. Nowadays Ciphertext-Policy Attribute-Based Encryption (CP-ABE) has been adopted. Because in the existing Ciphertext - Policy Attribute-Based Encryption schemes, there exists a single authority and this authority will be responsible for the verification of users, the generation and also the distribution of secret keys to the users. Users will have to wait for a long time to obtain their secret keys which results in the reduction of the efficiency of the system. Even though many multi authority schemes have been suggested, these schemes are still unable to reduce the drawbacks of the existing scheme and also the lower efficiency, because each of the authorities independently manages a separate attribute set. In this paper we propose a framework to eliminate the overload on single authority and enhance the efficiency. This framework aims in providing multiple attribute authorities to share the workload of user legitimacy verification. And we also introduce a central authority in our scheme to distribute the secret keys for the users whose identity is verified. In our scheme, each authority manages the whole attribute set.