P²B-Trace: Privacy-Preserving Blockchain-based Contact Tracing to Combat Pandemics

The eruption of COVID-19 has caused a unprecedented global crisis. Contact tracing, as a pillar of communicable disease control in public health for decades, has shows its effectiveness on COVID-19 control. Despite intensive research on contact tracing, existing schemes are vulnerable to attacks and can hardly simultaneously meet the requirements of data privacy and authenticity. The problem of designing a privacy-preserving contact tracing framework to ensure the authenticity of tracing procedure has not been sufficiently studied and remains open. In this paper, we propose BP$^2$-Trace, a privacy-preserving contact tracing initiative based on the blockchain system. First, a novel authenticated data structure is proposed for blockchain to prevent users' local contact data fraud with privacy concerns. Then, a zero-knowledge data authentication scheme is proposed based on the blockchain to verify the authenticity of local contact data, while preserving the patient's privacy. Finally, a decentralized contact detection scheme is designed to match close proximity and generate verifiable proofs without revealing the client's privacy. We implement BP$^2$-Trace and conduct extensive experiments by utilizing the popular blockchain framework. The evaluation results demonstrate the effectiveness of our proposed BP$^2$-Trace system.