France releases a voluntary contact tracing app

The French government has released a contract tracing app, called StopCovid, to notify people when they’ve been in contact with someone who is later diagnosed with COVID-19, as reported by Bloomberg. Usage of the app is entirely voluntary in France, although the effectiveness of contact tracing depends on how many people are using it.

Buoyed by the release of the Apple-Google framework for contact tracing, many countries, including Italy and Switzerland, have released contact tracing apps in the last few weeks. But the French app has been in development since before Apple and Google released their APIs. StopCovid uses ROBERT, a contact tracing protocol developed by the Pan-European Privacy-Preserving Proximity Tracing project. It works by assigning each user a permanent, pseudonymous ID, which is then used to create several ephemeral IDs. The ephemeral IDs are communicated to other nearby devices via Bluetooth. If someone reports that they’ve been diagnosed with COVID-19, the server flags all of the ephemeral IDs associated with their permanent ID. This triggers a notification for anyone who’s been in contact with one or more of those ephemeral IDs.