A Blockchain-based Medical Data Marketplace with Trustless Fair Exchange and Access Control

The unprecedented growth of decentralized technologies and the abundance of healthcare data creates numerous opportunities for the digital healthcare industry and poses major challenges for data security. In this paper, we propose a novel decentralized blockchain-based medical data marketplace in which medical record sellers can sell their data to interested buyers, e.g., pharmaceutical corporations. Sellers use a smart contract to exchange their records with buyers for a digital currency. In our model, sellers can enforce flexible access control policy on the encrypted records while allowing the buyers to verify the correctness of the encrypted records without revealing any information about the records using the developed zk-SNARK protocol. In addition, sellers acquire a proof-of-delivery to redeem buyers' contingent payments by exchanging a record access key for a buyer signature using the developed trustless zero-knowledge contingent payment protocol. Our security analysis proves that our model is secure against malicious behaviors of both dishonest sellers/buyers. Performance evaluation indicates that the GAS cost on Etherume blockchain and the computational cost of the cryptographic operations are low.