With the rapid development of network and storage technology, cloud storage has become a new service mode, while data sharing\nand user revocation are important functions in the cloud storage. Therefore, according to the characteristics of cloud storage, a\nrevocable key-aggregate encryption scheme is put forward based on subset-cover framework. The proposed scheme not only has\nthe key-aggregate characteristics, which greatly simplifies the user�s key management, but also can revoke user access permissions,\nrealizing the flexible and effective access control. When user revocation occurs, it allows cloud server to update the ciphertext so\nthat revoked users can not have access to the new ciphertext, while nonrevoked users do not need to update their private keys. In\naddition, a verification mechanism is provided in the proposed scheme, which can verify the updated ciphertext and ensure that\nthe user revocation is performed correctly. Compared with the existing schemes, this scheme can not only reduce the cost of key\nmanagement and storage, but also realize user revocation and achieve user�s access control efficiently. Finally, the proposed scheme\ncan be proved to be selective chosen-plaintext security in the standard model.
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