Contact tracing is a very effective way to control the COVID-19-like
pandemics. It aims to identify individuals who closely contacted an infected
person during the incubation period of the virus and notify them to quarantine.
However, the existing systems suffer from privacy, security, and efficiency
issues. To address these limitations, in this paper, we propose an efficient
and privacy-preserving Blockchain-based infection control system. Instead of
depending on a single authority to run the system, a group of health
authorities, that form a consortium Blockchain, run our system. Using
Blockchain technology not only secures our system against single point of
failure and denial of service attacks, but also brings transparency because all
transactions can be validated by different parties. Although contact tracing is
important, it is not enough to effectively control an infection. Thus, unlike
most of the existing systems that focus only on contact tracing, our system
consists of three integrated subsystems, including contact tracing, public
places access control, and safe-places recommendation. The access control
subsystem prevents infected people from visiting public places to prevent
spreading the virus, and the recommendation subsystem categorizes zones based
on the infection level so that people can avoid visiting contaminated zones.
Our analysis demonstrates that our system is secure and preserves the privacy
of the users against identification, social graph disclosure, and tracking
attacks, while thwarting false reporting (or panic) attacks. Moreover, our
extensive performance evaluations demonstrate the scalability of our system
(which is desirable in pandemics) due to its low communication, computation,
and storage overheads.

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