An authenticated field-free multi-keyword data search scheme for the Internet of Health Things

Abstract In the Internet of Health Things (IoHT), patients upload encrypted health data to the cloud, enabling doctors to access records remotely, and make timely diagnoses beyond geographical limits. A potential challenge is the efficient retrieval of specific medical data by doctors from large-scale encrypted datasets. Identity-based encryption with keyword search offers a feasible solution and addresses certificate management problem. Multi-keyword search is essential in IoHT as it improves retrieval efficiency. This paper proposes an SM9-based authenticated field-free multi-keyword searchable encryption scheme. The proposed scheme overcomes the limitation of existing SM9-based searchable encryption schemes that only support single-keyword search and provides resistance against keyword guessing attack, enhancing both functionality and security. We use the polynomial technique to achieve multi-keyword search while eliminating keyword field restrictions, resulting in high flexibility. Our scheme is proven to satisfy secure index indistinguishability and search token indistinguishability. Theoretical analysis and experimental results demonstrate its effectiveness. In multi-keyword search scenarios, compared with existing SM9-based schemes that require repeated executions of the index generation algorithm, our scheme reduces computational overhead by at least 92% with a single execution and further decreases index storage cost by at least 45%. Moreover, it improves search efficiency by at least 73%, making it more suitable for the IoHT.