Ensuring Digital Sovereignty in Cross-chain EHR Sharing: A Relay-as-a-Service Approach for Secure Healthcare Interoperability

Electronic Health Records (EHRs) stored in cloud environments often face privacy challenges in healthcare data management due to the divide between patient ownership and institutional control. Blockchain technology offers a promising solution with its features of immutability and traceability. However, existing blockchain-based approaches for EHR privacy preservation are limited to single institutions and fail to address the critical need for cross-chain compatibility and digital sovereignty. To bridge this gap, we propose two novel strategies: Polkadot-based Cross-chain for EHR-preserving Blockchain (PCEB) and Relay-as-a-Service-based Cross-chain for EHR-preserving Blockchain (RaSCEB). PCEB utilizes Polkadot's relay communication to securely share EHR data across multiple healthcare networks while preserving patient privacy and ensuring digital sovereignty. RaSCEB introduces Relay-as-a-Service (RaaS) to enable seamless EHR sharing across blockchain ecosystems, empowering patients with control over their data while maintaining regulatory compliance and sovereignty over their digital health records. Both approaches are validated through comprehensive security analysis and performance evaluations. We also present an interoperability framework tailored for permissioned blockchain networks, emphasizing trust derived from consensus mechanisms. Our work addresses the urgent need for cross-chain compatibility in EHR privacy preservation and advances interoperability solutions while safeguarding digital sovereignty in healthcare and beyond.