Contact tracing & privacyBluetooth Signals from Your Smartphone Could Automate COVID-19 Contact Tracing While Preserving Privacy

By Kylie Foy

Published 15 April 2020

Imagine you’ve been diagnosed as Covid-19 positive. Health officials begin contact tracing to contain infections, asking you to identify people with whom you’ve been in close contact. The obvious people come to mind — your family, your coworkers. But what about the woman ahead of you in line last week at the pharmacy, or the man bagging your groceries? Or any of the other strangers you may have come close to in the past 14 days? Researchers are developing a system that augments “manual” contact tracing by public health officials, while preserving the privacy of all individuals. The system enables smartphones to transmit “chirps” to nearby devices could notify people if they have been near an infected person.

Imagine you’ve been diagnosed as Covid-19 positive. Health officials begin contact tracing to contain infections, asking you to identify people with whom you’ve been in close contact. The obvious people come to mind — your family, your coworkers. But what about the woman ahead of you in line last week at the pharmacy, or the man bagging your groceries? Or any of the other strangers you may have come close to in the past 14 days?

A team led by MIT researchers and including experts from many institutions is developing a system that augments “manual” contact tracing by public health officials, while preserving the privacy of all individuals. The system relies on short-range Bluetooth signals emitted from people’s smartphones. These signals represent random strings of numbers, likened to “chirps” that other nearby smartphones can remember hearing.

If a person tests positive, they can upload the list of chirps their phone has put out in the past 14 days to a database. Other people can then scan the database to see if any of those chirps match the ones picked up by their phones. If there’s a match, a notification will inform that person that they may have been exposed to the virus, and will include information from public health authorities on next steps to take. Vitally, this entire process is done while maintaining the privacy of those who are Covid-19 positive and those wishing to check if they have been in contact with an infected person.

“I keep track of what I’ve broadcasted, and you keep track of what you’ve heard, and this will allow us to tell if someone was in close proximity to an infected person,” says Ron Rivest, MIT Institute Professor and principal investigator of the project. “But for these broadcasts, we’re using cryptographic techniques to generate random, rotating numbers that are not just anonymous, but pseudonymous, constantly changing their ‘ID,’ and that can’t be traced back to an individual.”

This approach to private, automated contact tracing will be available in a number of ways, including through the privacy-first effort launched at MIT in response to Covid-19 called SafePaths. This broad set of mobile apps is under development by a team led by Ramesh Raskar of the MIT Media Lab. The design of the new Bluetooth-based system has benefited from SafePaths’ early work in this area.