Blockchain-based multi-user certificateless encryption with keyword search for electronic health record sharing

Nowadays, with the rapid development of smart health-care based on electronic health records, it remarkably supplies a promising way to alleviate the shortage of medical resources and improve medical efficiency. Meanwhile, data in electronic health records are sensitive and require protection against unauthorized access. However, most previous electronic health records sharing schemes are vulnerable to data leakage and forgery. To address these challenging problems, we propose a new electronic health record sharing scheme. We use the certificateless cryptosystem to encrypt keywords, which solves the certificate management problem and key escrow problem. The proposed scheme also supports multi-user search and the user authorization table can be used to modify access permissions of medical data users. Besides, the root values of the Merkle trees are written into the blockchain to ensure anti-tampering, integrity and traceability of search results. Moreover, a smart contract enables a fair transaction between cloud server provider and medical data users without trusted third parties. We prove that the proposed scheme is secure against the keyword guessing attack in the random oracle model. Furthermore, performance analysis demonstrates that our scheme has greater computational efficiency compared with other related schemes.