Increasing the lifetime for what are currently "daily keys" reduces the precision of the contact reporting - e.g. your example of a week means that a positive user would need to report at least 3 weeks of keys, so someone can now do correlation over 3 weeks instead of X days.
There's no inclusion of location data as that has no value - the only thing that this protocol cares about was whether you were in the vicinity of someone who has tested positive for cover-19, and so suggest you get tested. Knowing where you are/were has no value for that purpose.
I think he was trying to say you could reduce the computation by narrowing the space-time radius, then searching for matches. Even a state-level restriction would be enough to substantially narrow down the possible matches without sacrificing anonymity.
Comments
Increasing the lifetime for what are currently "daily keys" reduces the precision of the contact reporting - e.g. your example of a week means that a positive user would need to report at least 3 weeks of keys, so someone can now do correlation over 3 weeks instead of X days.
There's no inclusion of location data as that has no value - the only thing that this protocol cares about was whether you were in the vicinity of someone who has tested positive for cover-19, and so suggest you get tested. Knowing where you are/were has no value for that purpose.
I think he was trying to say you could reduce the computation by narrowing the space-time radius, then searching for matches. Even a state-level restriction would be enough to substantially narrow down the possible matches without sacrificing anonymity.