  While prospect of tracking mobile devices' users is widely discussed all over
European countries to counteract COVID-19 propagation, we propose a Bloom
filter based construction providing users' location privacy and preventing mass
surveillance. We apply a solution based on Bloom filters data structure that
allows a third party, a government agency, to perform some privacy-preserving
set relations on a mobile telco's access logfile. By computing set relations,
the government agency, given the knowledge of two identified persons, has an
instrument that provides a (possible) infection chain from the initial to the
final infected user no matter at which location on a worldwide scale they are.
The benefit of our approach is that intermediate possible infected users can be
identified and subsequently contacted by the agency. With such approach, we
state that solely identities of possible infected users will be revealed and
location privacy of others will be preserved. To this extent, it meets General
Data Protection Regulation (GDPR)requirements in this area.
