  The coronavirus disease 2019 (COVID-19) pandemic has caused an unprecedented
health crisis for the global. Digital contact tracing, as a transmission
intervention measure, has shown its effectiveness on pandemic control. Despite
intensive research on digital contact tracing, existing solutions can hardly
meet users' requirements on privacy and convenience. In this paper, we propose
BU-Trace, a novel permissionless mobile system for privacy-preserving
intelligent contact tracing based on QR code and NFC technologies. First, a
user study is conducted to investigate and quantify the user acceptance of a
mobile contact tracing system. Second, a decentralized system is proposed to
enable contact tracing while protecting user privacy. Third, an intelligent
behavior detection algorithm is designed to ease the use of our system. We
implement BU-Trace and conduct extensive experiments in several real-world
scenarios. The experimental results show that BU-Trace achieves a
privacy-preserving and intelligent mobile system for contact tracing without
requesting location or other privacy-related permissions.
