Clover: an Anonymous Transaction Relay Protocol for the Bitcoin P2P Network

TL;DR

Clover is a new Bitcoin transaction relay protocol that enhances user privacy by significantly reducing the ability of adversaries to trace transaction sources, without complex network graph constructions.

Contribution

We introduce Clover, a simple and effective relay protocol that improves privacy in Bitcoin networks by reducing deanonymization risks without complex modifications.

Findings

Deanonymization accuracy reduced by up to 10 times compared to Diffusion

Clover does not require building propagation graphs

The protocol is simple and effective for real-world deployment

Abstract

The Bitcoin P2P network currently represents a reference benchmark for modern cryptocurrencies. Its underlying protocol defines how transactions and blocks are distributed through all participating nodes. To protect user privacy, the identity of the node originating a message is kept hidden. However, an adversary observing the whole network can analyze the spread pattern of a transaction to trace it back to its source. This is possible thanks to the so-called rumor centrality, which is caused by the symmetry in the spreading of gossip-like protocols. Recent works try to address this issue by breaking the symmetry of the Diffusion protocol, currently used in Bitcoin, and leveraging proxied broadcast. Nonetheless, the complexity of their design can be a barrier to their adoption in real life. In this work, we propose Clover, a novel transaction relay protocol that protects the source of transaction messages with a simple, yet effective, design. Compared to previous solutions, our protocol does not require building propagation graphs, and reduces the ability of the adversary to gain precision by opening multiple connections towards the same node. Experimental results show that the deanonymization accuracy of an eavesdropper adversary against Clover is up to 10 times smaller compared to Diffusion.