Private Transaction Retrieval for Lightweight Bitcoin Client

In the current Bitcoin network, lightweight clients outsource most of the computational and storage tasks to full blockchain nodes in order to run on resource-constrained devices, such as mobile phones. In the interactions with the full node, the lightweight client leaks considerable information about the Bitcoin transactions or addresses associated with this client. Therefore, the benefit of using lightweight client comes at costs of privacy. Existing solutions cannot support the lightweight client to retrieve the relevant transactions from the full node in an efficient and privacy-preserving way. In this paper, we propose a new approach to protect the privacy of lightweight clients in Bitcoin. Our main idea is to use private information retrieval (PIR) to guarantee that the lightweight clients can fetch the relevant transactions from untrusted full nodes without revealing to those nodes which particular transactions are being fetched. Directly using existing PIR scheme incurs high communication overhead for lightweight clients. Therefore, we propose an optimized protocol utilizing two-step PIR to efficiently retrieve the queried transactions without leaking sensitive query information. We developed a prototype implementation to demonstrate the feasibility of our proposed scheme.