Adding Location Context to Apple/Google Exposure Notification Bluetooth API:

MIT SafePaths Encryption Proposals for GPS + Bluetooth

SafePaths Protocol to combine GPS + GAEN: We propose a protocol that stays very close to the GAEN protocol based on the idea that GPS information is available to a healthy phone only if exposed. If Alice is healthy and comes in proximity to Bob who was later diagnosed Covid+, Alice will be able to see the location (and time) of that encounter but the rest of her location history remains invisible or encrypted. This is our suggested modification to GAEN. We also propose other three ideas that do not require changes to GAEN protocol but require Apple/Google to allow such apps to access GPS privately on device and run other servers.

The 4 privacy preserving solutions to provide location-time context can be summarized as follows : The idea is to use BLE for proximity and GPS for context (but not proximity).

1. GPS logged on device, data does not leaves the phone, no visualization

2. GPS + time blurred and logged on phone, data does not leaves the phone, no visualization

3. FindMy variant: Encrypt RPI

4. GAEN variant: Encrypt your own GPS with DailyKey and Broadcast over BLE

We recommend Option 2 if BT as well as GPS API can co-exist

We recommend Option 4D below if encrypted GPS can only be part of the BT payload.

Please use this document for GAEN terminology which we also use here