Metadata Privacy Preservation for Blockchain-Based Healthcare Systems

Blockchain-based healthcare systems provide a patientcentric and accountable way to manage and share electronic health records. Thanks to its unique features, the blockchain is employed to record the metadata and to carry out access control. Nevertheless, the transparent nature of blockchain also poses a new challenge to these systems. We identify that the metadata stored on the blockchain leaks the relationship between doctors and patients. Based on this relationship, the adversary can launch linkage attacks to infer patients' information. Hence, it is necessary to protect metadata privacy. However, strong privacy protection may reduce accountability. Striking a balance between accountability and privacy preservation is a major challenge for the blockchain and its applications. In this paper, we first elaborate on the reasons why the metadata could leak the privacy of patients in blockchain-based healthcare systems. After that, we propose privacy-preserving and accountable protocols to deal with this problem for two different healthcare scenarios: the single doctor case and the group consultation case. Finally, the theoretical analysis demonstrates the practicality of our protocols.