OblivChain: Enabling Oblivious Queries for Blockchain Light Clients with Malicious Security

The blockchain database has gained increasing popularity with the prosperity of cryptocurrencies and decentralized applications. To address storage overhead issues, the light client, which only stores lightweight blockchain data and accesses on-chain data via a full node, has been introduced. However, the method of accessing outsourced requests raises significant privacy concerns, including the integrity of returned results and leakage of block access history. In this paper, we propose OblivChain, a secure and efficient oblivious query scheme for blockchain systems. We utilize the multi-server architecture to provide decentralized query services for full nodes against malicious security threats. To hide sensitive access information, we employ a customized design of the read-only ORAM with enhanced query performance. We present a comprehensive formal security analysis and experimental evaluations to demonstrate the practicality of our design.