BlindChain: Keeping Query Privacy in Blockchain Out of Sight

Blockchain allows full nodes and light nodes coexist to support users with limited resources. Any query from light nodes must be forwarded to full nodes that maintain the entire blockchain data. However, outsourcing queries to full nodes may invade users’ privacy. Most existing works of privacy-preserving blockchain query systems focus on deploying Software Guard Extensions (SGX) for every full node or resorting to expensive cryptographic tools such as ORAM, incurring heavy communication and computation overheads. In this paper, we propose a blockchain system BlindChain that can protect query privacy of light nodes and verify correctness of query results with lightweight overhead. BlindChain integrates Function Secret Sharing (FSS) into blockchain, requiring only a small part of full nodes to be configured with SGX. We first introduce an SGX-based garrison to meet the trust model requirements of the FSS in the context of blockchain. Then, we design a novel authenticated data structure for BlindChain to verify result correctness. Finally, we propose an optimization technique based on parallel processing to improve the query performance. We demonstrate the privacy-preserving property of BlindChain through rigorous security analysis. Experiment results show that BlindChain outperforms the previous works in terms of both computation and communication overheads.