A lattice-based group signature with backward unlinkability for medical blockchain systems

Abstract

To address issues of data island existing in traditional medical information systems and privacy leakage caused by patient-doctor association in medical data sharing, we first propose a secure medical data sharing scheme that combines blockchain and group signatures. The scheme stores the encrypted and desensitized real medical data in the InterPlanetary File System (IPFS) and uploads the returned data access credentials to the blockchain, significantly reducing the blockchain storage overhead. Then, we construct a lattice-based group signature scheme with backward unlinkability for medical data sharing environments, which effectively addresses privacy leakage issues caused by linkability. The group signature scheme is based on the computational intractability of the Short Integer Solution (SIS) problem, achieving anti-quantum security. To optimize the sampling efficiency, the scheme employs a bimodal Gaussian distribution for the generation of signature components. In addition, we formally demonstrate that the scheme achieves correctness and security, satisfying traceability, unforgeability, anonymity, and backward unlinkability. Finally, through extensive performance evaluation, our proposed group signature scheme performs better compared to existing similar cryptographic schemes. It achieves significant improvements in two critical aspects: key size and signature size. These parameters maintain linear independence from the group size, ensuring scalability in large-group applications. And the size of the revocation list is effectively reduced by only storing user tokens that have been revoked before expiration.