I’m not sure if this is exactly what Apple is proposing, but it’s a good explanation of how to use some concepts from encryption to gather data and preserve anonymity.
An analysis of data leakage and a twitter thread from Moxie Marlinspike.
Quick summary here
PRing your twitter, not cool. From the link:
device key -> KDF -> daily key -> HMAC -> 15-minute rolling key
If infected, you send your device key to the server which distributes it to everyone
Anyone receives list of device keys of the infected, so they can recompute rolling keys to look for matches.
You don’t send your device key, you send your list of daily keys for the duration of your contagion.
Whoops, thanks. Corrected.
Why would that be not ok?
Anyway, Moxie Marlinspike has some further discussion here: https://twitter.com/moxie/status/1248707315626201088?s=21
And some more discussion: https://lobste.rs/s/l5aoh8/leakage_paths_for_apple_google_bluetooth
If only they collaborate on expanding iMessages..