One of the effective way to ensure data security in cloud computing is data access control. Due to untrusted and outsourcing cloud server, the control of data access became a challenging issue in cloud computing. One of the most suitable technology for data control in cloud is Ciphertext-Policy Attributebased Encryption (CP-ABE) , because it gives control to the data owners on direct access policies. It is somewhat difficult to apply existing Ciphertext-Policy Attribute-based Encryption

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... scheme to cloud data access control because of the attribute revocation problem. In this paper, we design an revocable, expressive and well-organized data access control for multi authority cloud storage, where there are multiple authorities co exist and each authority is able to issue attributes independently. We propose a revocable multi-authority Ciphertext-Policy Attributebased Encryption scheme, and apply it is the principal techniques to design the data access control scheme. Our revocation attribute method can efficiently achieve both backward security and forward security. The analysis results show that our proposed data access control scheme is secure in the casual oracle model and is more efficient than previous works.