Paper 2020/630

ContactChaser: A Simple yet Effective Contact Tracing Scheme with Strong Privacy

Zhiguo Wan and Xiaotong Liu

Abstract

The COVID-19 pandemic is a severe threat to both lives and economics throughout the world. Advanced information technology can play an important role to win this war against this invisible enemy. The most effective way to fight COVID-19 is quarantining infected people and identifying their contacts. Recently, quite a few Bluetooth-based contact tracing proposals have been proposed to identify who has come into contact with infected people. The success of a contact tracing system depends on multiple factors, including security and privacy features, simplicity and user-friendliness etc. More importantly, it should help the health authority to effectively enforce contact tracing, so as to control spreading of the vital virus as soon as possible. However, current proposals are either susceptible to security and privacy attacks, or expensive in computation and/or communication costs. In this paper, we propose ContactChaser, a simple but effective contact tracing scheme based on group signature, to achieve strong security and privacy protection for users. ContactChaser only requires a health authority to issue group private keys to users for only once, without frequently updating keys with the authority. It helps the authority to find out the close contacts of infected people, but just leaks the minimum information necessary for contact tracing to the health authority. Specially, the contact relationship is protect against the authority, which only knows the close contacts of infected people. ContactChaser is able to prevent most attacks, especially relay and replay attacks, so that it can effectively avoid false alerts and reduce unreported contacts. We give a detailed analysis of ContactChaser’s security and privacy properties as well as its performance. It is expected ContactChaser can contribute to the design and development of contact tracing schemes.