COVID-19: A welcome effort from Apple and Google
To prevent the spread of the COVID-19, we have explored Bluetooth-based contact-tracing techniques. Other solutions based on GPS, antenna towers or local wifi triangulation, are not precise or reliable enough.
Bluetooth-based contact-tracing requires devices to advertise their presence, and scan for other devices around. Advertising is based on anonymous identifiers and raises many privacy issues. Knowledge of only four places and times can lead to re-identification, with a 95% accuracy. The solution is to roll the advertised anonymous identifiers regularly. Manufacturers like Apple have added a security measure to do it every 15 minutes to prevent massive tracking of their clients.
Another security from Apple prevents applications from constantly advertising: Bluetooth advertisement fully works only when an app is in the foreground. Some background advertisement is still possible, but it relies on a non-standard protocol which does not work across platforms and is done on a best-effort basis.
In a nutshell, cross-platform tracing requires the apps to remain open and in the foreground. It is unlikely.
As a means to address these issues, Apple and Google jointly announced a new feature yesterday, to allow always-on Bluetooth-based advertisement. This feature is scheduled for mid-May and will be activated only during the pandemic. Users will have to opt-in: it is a welcome effort and great news.
We are adapting our design to be compatible with Apple and Google's specifications.