Cipher text-Policy Attribute-base Encryption (CP-ABE) is regarded as one of the most suitable technologies for data access control in cloud storage. In almost all existing CP-ABE schemes, it is assumed that there is only one authority in the system responsible for issuing attributes to the users. However, in many applications, there are multiple authorities co-exist in a system and each authority is able to issue attributes independently. In this paper, we design an access control framework for multi-authority systems and propose an efficient and secure multi-authority access control scheme for cloud storage. We first design an efficient multi-authority CP-ABE scheme that does not require a global authority and can support any LSSS access structure. Then, we prove its security in the random oracle model. We also propose a new technique to solve the attribute revocation problem in multi-authority CP-ABE systems. The analysis and simulation results show that our multi-authority access control scheme is scalable and efficient.
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