Server-aided revocable attribute-based encryption for cloud Server-aided revocable attribute-based encryption for cloud computing services computing services and WANG, Guilin. Server-aided revocable attribute-based encryption for cloud computing services. (2020). Concurrency and Computation: Practice and Experience. Research Collection School Of Information Systems. Abstract Attribute-based encryption (ABE) has been regarded as a promising solution in cloud computing services to enable scalable

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... access control without compromising the security. Despite of the advantages, efficient user revocation has been a challenge in ABE. One suggestion for user revocation is using the binary tree in the key generation phase of an ABE scheme, which enables a trusted key generation center (KGC) to periodically distributes the key update information to all non-revoked users over a public channel. This revocation approach reduces the size of key updates from linear to logarithmic in the number of users. But it requires each user to keep a private key of the logarithmic size, and asks each non-revoked user to periodically update his/her decryption key for each new time period. To further optimize user revocation in ABE, a server-aided revocable ABE (SR-ABE) scheme has been proposed, in which almost all workloads of users incurred by the user revocation are outsourced to an untrusted server, and each user only needs to store a private key of the constant size. In addition, SR-ABE does not require any secure channel for the key transmission, and a user only needs to perform a small amount of calculations to decrypt a ciphertext. In this paper, we revisit the notion of SR-ABE, and present a generic construction of SR-ABE, which can transform a revocable ABE (RABE) scheme to an SR-ABE scheme. In addition, we give an instantiation of SR-ABE by applying the generic construction on a concrete RABE scheme, and implement an instantiation of SR-ABE and an RABE scheme to evaluate the performance of SR-ABE.