Towards Revocable Fine-Grained Encryption of Cloud Data: Reducing Trust upon Cloud

ABE (Attribute-based encryption) is capable of fine-grained data encryption, and thus has been studied for secure cloud data sharing. While a number of efforts have been dedicated to resolving the user revocation issue in the multi-user cloud data sharing setting, the trust assumption placed upon the cloud server is still high. In this work, we identify the necessity of achieving verifiability of cloud decryption in the proxy-assisted user revocation approach, so as to weaken the trust assumption on the cloud server. We further formulate a model for the system, and present two independent constructions following the formulation. Experimental results show the practicality of our proposed schemes.