Lattice Multiauthority Attribute‐Based Signcryption Scheme for Blockchain‐Based Personal Health Record Sharing

The sharing of personal health records (PHRs) benefits healthcare by improving disease diagnosis, treatment, and early outbreak detection. However, outsourcing PHRs for storage exposes data to risks such as tampering and unauthorized access. Ensuring the security of PHRs is crucial, especially when shared via third‐party servers. A secure sharing model must guarantee privacy, unforgeability, and fine‐grained access control based on the data owner’s policies. In this paper, we propose a lattice‐based multiauthority attribute‐based signcryption (MA‐ABSC) scheme tailored for secure and privacy‐preserving PHR sharing in a blockchain‐enabled environment. The scheme combines the postquantum security of lattice cryptography with fine‐grained access control and decentralized trust enabled by blockchain. Our construction supports multiple attribute management authorities (AMAs) and ensures ciphertext‐policy enforcement without central key escrow. We implemented the scheme using the PALISADE lattice cryptography library and evaluated its performance. Experimental results show that for a lattice dimension n = 1024, the signcryption time is approximately 190 ms, while the resulting ciphertext size is around 13.2 KB. The scheme achieves verifiable outsourcing with tamper evidence via blockchain auditing and supports scalable key management across federated healthcare domains. Security and performance analyses demonstrate that our design is quantum resilient, efficient, and suitable for practical deployment in smart healthcare systems.