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In cloud computing, the sensitive data are required to be encrypted before being outsourced to the server, which introduce a heavy computation overhead for key derivation and data management when dynamic hierarchical access control is desired. In this paper, we address this challenging problem by delegating the computation intensive task, such as data re-encryption, key distribution and derivation to cloud servers. Only bilinear pairing and random padding are used in our construction. Extensive analysis shows that the proposed scheme achieves scalability and dynamic simultaneously, and is proved to be secure formally.