Efficient Fine-Grained Forward Secure Encryption Scheme Based on Attributes in Mobile Healthcare

In mobile health (mHealth), people's personal health records (PHRs) will be captured in real time. It will be managed by the cloud server and shared to authorized users. This will enable people to enjoy more timely medical services. The confidentiality and unauthorized access of PHRs is guaranteed by the attribute set encryption (CP-ABE) with ciphertext policy. However, existing CP-ABE schemes not only face heavy computation cost and storage overhead, but also once the data user's key is leaked, all the data that can be decrypted by that user will also be leaked. It is a huge challenge to ensure the forward security of data. Most of the existing solutions only support coarse-grained data protection and cannot solve the problem of excessive computation cost and storage overhead. In this paper, based on the enhanced Policy-based Puncturable Encryption (P- PUN-ENC) primitive and and-gate access structure,we propose an efficient fine-grained forward secure encryption scheme based on attributes, named EFFS-CP-ABE. In EFFS-CP-ABE, data users are able to protect the corresponding data on the cloud in a policy-based manner accurately and permanently. In addition, to solve the problem of decryption cost in our solution, we combine the decryption outsourcing technique with our scheme. This allows the decryption process of our solution to be performed only 7 times with bilinear mapping. Also the length of the ciphertext of our scheme is constant. Extensive simulation results and performance evaluations demonstrate the safety, effectiveness and practicality of the EFFS-CP-ABE scheme.