Optimized Blockchain-Based EMR Sharing via Secure Channel-Free Universal Designated Verifier Signature Proofs

The sharing of electronic medical records (EMR) significantly enhances disease research and healthcare system efficiency. However, outsourcing EMRs to cloud servers introduces risks such as tampering and malicious propagation by recipients. Existing solutions combining blockchain and Universal Designated Verifier Signature Proofs (UDVSP) mitigate these risks but rely on secure channels for key sharing, adding communication and computation costs that hinder deployment. In this paper, we introduce the first Secure Channel-Free Universal Designated Verifier Signature Proofs (SCF-UDVSP) scheme, leveraging simplified cryptographic techniques like the Σ-protocol and public key encryption. Integrating SCF-UDVSP with blockchain, we develop an optimized EMR sharing system that effectively prevents these attacks including tampering and malicious propagation. Security proofs and performance analysis validate the feasibility and effectiveness of our proposed system. Compared to existing UDVSP solutions, our approach reduces computational costs by approximately 59.3% without increasing communication overhead, while also eliminating the need for establishing a secure channel.