  Contact tracing is an essential tool for public health officials and local
communities to fight the spread of novel diseases, such as for the COVID-19
pandemic. The Singaporean government just released a mobile phone app,
TraceTogether, that is designed to assist health officials in tracking down
exposures after an infected individual is identified. However, there are
important privacy implications of the existence of such tracking apps. Here, we
analyze some of those implications and discuss ways of ameliorating the privacy
concerns without decreasing usefulness to public health. We hope in writing
this document to ensure that privacy is a central feature of conversations
surrounding mobile contact tracing apps and to encourage community efforts to
develop alternative effective solutions with stronger privacy protection for
the users. Importantly, though we discuss potential modifications, this
document is not meant as a formal research paper, but instead is a response to
some of the privacy characteristics of direct contact tracing apps like
TraceTogether and an early-stage Request for Comments to the community.
  Date written: 2020-03-24
  Minor correction: 2020-03-30
