Pretty good illustration of how private and secure contact tracing can work here: https://ncase.me/contact-tracing/
Not sure whether that's what this implementation would look like.
Not sure whether that's what this implementation would look like.
> alice can also hide messages from times she wants to keep private
If there's a need for this, doesn't that imply that the scheme does not actually keep Alice's privacy in all situations?
Furthermore:
> the random messages give the hospital NO INFO on where Alice was
This seems to assume that the hospital (or anyone with access to the data, such as governments) didn't capture the broadcast messages together with their location. With enough Bluetooth receptors in busy areas, a government could easily find out where Alice had been by looking up each of her messages in their list of message/location pairs?
Experts can probably come up with nastier and/or easier exploits...
In particular, given an adversary who has several points (receiving these codes) and knows the receiving location of each of these points can de-anonymize a person "A" who is COVID positive if they know, e.g., a minimal amount of A's usual daily movements (from cellphone tower location, for example).
That being said, the government probably has better ways of knowing who has COVID-19 and other infectious diseases :)
Once the crisis is over, they'll continue to use such "safe" apps, for other purposes ...