Privacy-Preserving COVID-19 Contact Tracing App: A Zero-Knowledge Proof Approach

In this paper, we propose a privacy-preserving contact tracing app for COVID-19. The app allows users to be notified, if they have been a close contact with a confirmed patient. Our protocol is the most comprehensive and balanced privacy-preserving contact tracing solution to date. Our protocol strikes a balance between security, privacy and scalability. In terms of privacy, it allows all users to hide his past location and contact history with respect to the Government. Yet, all users can check whether he had a close contact with a confirmed patient without learning the identity of the patient. We use a zero-knowledge protocol to ensure that user privacy is protected. In terms of security, no user can send fake message to the system to launch a false positive attack. We give a formal security model and give a security proof for our protocol. In terms of scalability, we have implemented our protocol into Android smartphone and our evaluation result shows its practicality.