SPChain: Blockchain-based medical data sharing and privacy-preserving eHealth system

The sharing of electronic medical records (EMRs) has great positive significance for research on disease and epidemic prevention. Recently, blockchain-based eHealth systems have achieved great success in terms of EMRs sharing and management, but there still remain some challenges. Permissioned blockchain-based solutions provide high throughput and scalability, but may suffer from rollback attacks and lead to privacy leakage. Designs based on the public blockchain, on the other hand, are more open and secure, but sacrifice scalability and have no incentives for medical institutions to join into the systems. Moreover, data retrieval in blockchain-based eHealth systems is inefficient because of the basic blockchain structure. To solve the above problems, we propose a blockchain-based medical data sharing and privacy-preserving eHealth system named SPChain. To achieve quick retrieval, we devise special keyblocks and microblocks for patients to store their EMRs. A reputation system is also constructed to motivate medical institutions to participate in SPChain. By using proxy re-encryption schemes, SPChain achieves medical data sharing for patients in a privacy-preserving manner. To evaluate SPChain, we leverage the distribution of miners in the real world to test the system's performance and ability to resist mentioned attacks. The results show that SPChain can achieve high throughput (220 TPS) with low storage overhead. Compared with the existing schemes, SPChain achieves lower time complexity in terms of data retrieving, and can resist proposed blockchain attacks as well as SPChain attacks.