Forward-Secure Customizable Data Sharing in Blockchain-based EHR Systems

Blockchain-based electronic healthcare record (EHR) systems function a trusted decentralized network for patients to store and share healthcare records. Owing to the transparency feature, blockchain can guarantee the integrity and consistency but not the privacy of healthcare records; hence encryption techniques are usually introduced to secure personal healthcare records. However, most encryption schemes in blockchain-based EHR systems are not very flexible for data sharing and may suffer from the key-leakage problem. In this paper, we propose a forward-secure customizable data sharing (fs-CDS) scheme for data owners (e.g., patients) to securely and flexibly share data in EHR systems. In fs-CDS, a data owner can generate a customized key with an identity so that the data consumer receiving this key can only access the data specified by the identity. Moreover, both the data owner and the data consumer may repeatedly update their keys to revoke the decryption capability for selected keywords, institution names or time periods, so that some important data remain confidential even if the keys are leaked. The proposed fs-CDS scheme supports unbounded number of key updates and achieves constant-size ciphertexts. Our security analysis and experimental evaluation show that the proposed fs-CDS scheme is secure and efficient, respectively.