Protecting Access Privacy for Bitcoin Lightweight Client Using Trusted Hardware

Through decentralized ledger, Bitcoin rebuilds trust and achieves payment verification. However, the verification of Bitcoin transactions requires nodes to download the whole blockchain, which is infeasible for resource-constraint devices. Traditional schemes tried to transfer most of the storage and computation tasks from a lightweight client to a full node. Nevertheless, these schemes would severely violate users' privacy since they would leak transaction ID and public-key address when a lightweight client queries the full node. To address this, we propose a privacy-preserving approach to secure queries of simplified payment verification (SPV) clients. Specifically, we design a d-differentially private mechanism based on trusted hardware such that semi-honest adversaries cannot acquire the real access pattern during shards retrieval phase. Data-oblivious primitives are adopted to prevent the internal search pattern leakage owing to side-channel attacks. Our scheme is more secure than traditional SPV schemes, and it is proved to satisfy d-differential privacy definition. Our prototype implementation with the Bitcoin blockchain dataset shows its practicality.