  COVID-19 is a severe global epidemic in human history. Even though there are
particular medications and vaccines to curb the epidemic, tracing and isolating
the infection source is the best option to slow the virus spread and reduce
infection and death rates. There are three disadvantages to the existing
contact tracing system: 1. User data is stored in a centralized database that
could be stolen and tampered with, 2. User's confidential personal identity may
be revealed to a third party or organization, 3. Existing contact tracing
systems only focus on information sharing from one dimension, such as
location-based tracing, which significantly limits the effectiveness of such
systems.
  We propose a global COVID-19 information sharing and risk notification system
that utilizes the Blockchain, Smart Contract, and Bluetooth. To protect user
privacy, we design a novel Blockchain-based platform that can share consistent
and non-tampered contact tracing information from multiple dimensions, such as
location-based for indirect contact and Bluetooth-based for direct contact.
Hierarchical smart contract architecture is also designed to achieve global
agreements from users about how to process and utilize user data, thereby
enhancing the data usage transparency. Furthermore, we propose a mechanism to
protect user identity privacy from multiple aspects. More importantly, our
system can notify the users about the exposure risk via smart contracts. We
implement a prototype system to conduct extensive measurements to demonstrate
the feasibility and effectiveness of our system.
