RE: Privacy-protecting contact tracer for COVID-19?

Here is a third approach:


1-      Everyone's path is recorded locally on their smartphone

2-      A public bulletin board (public ledger?) publishes the tracks of infected people in the following manner:

a.       Each track is divided into segments

b.       Each segment is represented as a 4d ball – just center and radius

c.       Each segment is signed with a different temporal DID, derived from the master DID of the patient

d.       Each ball is enlarged and offseted by a random displacement (as they do in differential privacy)

3-      When my smartphone finds that my path intersects with one of the segments, it requests a peer-to-peer anonymous communication with the owner of the segment.

4-      In the peer-to-peer communication both sides break their segment into smaller segments as in step 2 (sub step c is redundant) and communicate the scrambled sub-segments with each other. They do this iteratively for any overlapping sub-segments, until they get an intersecting point (2m radius) between their true paths.

Ouri.