Ciphertext-Policy Attribute-Based Signcryption With Verifiable Outsourced Designcryption for Sharing Personal Health Records

Personal health record (PHR) is a patient-centric model of health information exchange, which greatly facilitates the storage, access, and share of personal health information. In order to share the valuable resources and reduce the operational cost, the PHR service providers would like to store the PHR applications and health information data in the cloud. The private health information may be exposed to unauthorized organizations or individuals since the patient lost the physical control of their health information. Ciphertext-policy attribute-based signcryption is a promising solution to design a cloud-assisted PHR secure sharing system. It provides fine-grained access control, confidentiality, authenticity, and sender privacy of PHR data. However, a large number of pairing and modular exponentiation computations bring heavy computational overhead during designcryption process. In order to reconcile the conflict of high computational overhead and low efficiency in the designcryption process, an outsourcing scheme is proposed in this paper. In our scheme, the heavy computations are outsourced to ciphertext transformed server, only leaving a small computational overhead for the PHR user. At the same time, the extra communication overhead in our scheme is actually tolerable. Furthermore, theoretical analysis and the desired securing properties including confidentiality, unforgeability, and verifiability have been proved formally in the random oracle model. Experimental evaluation indicates that the proposed scheme is practical and feasible.