Large Universe Ciphertext-Policy Attribute-Based Encryption with Attribute Level User Revocation in Cloud Storage

Ciphertext-Policy Attribute-Based Encryption (CP-ABE), especially large universe CP-ABE that is not bounded with the attribute set, is getting more and more extensive application in the cloud storage. However, there exists an important challenge in original large universe CP-ABE, namely dynamic user and attribute revocation. In this paper, we propose a large universe CP-ABE with efficient attribute level user revocation, namely the revocation to an attribute of some user cannot influence the common access of other legitimate attributes. To achieve the revocation, we divide the master key into two parts: delegation key and secret key, which are sent to the cloud provider and user separately. Note that, our scheme is proved selectively secure in the standard model under "q-type" assumption. Finally, the performance analysis and experimental verification have been carried out in this paper, and the experimental results show that, compared with the existing revocation schemes, although our scheme increases the computational load of storage Service Provider (CSP) in order to achieve the attribute revocation, it does not need the participation of Attribute Authority (AA), which reduces the computational load of AA. Moreover, the user does not need any additional parameters to achieve the attribute revocation except of the private key, thus saving the storage space greatly.