Re: COVID-19 contacts tracker (Re: a brief pondering)

[John Wroclawski <[e-mail]>]

> On Apr 16, 2020, at 10:56 AM, Vittorio Bertola <vittorio.bertola=[e-mail]> wrote:
> 
>> Il 16/04/2020 09:18 Rob Sayre <[e-mail]> ha scritto:
>> It's not clear that any of these tracker proposals actually harm privacy. Certainly the government in most places can get this data from phone companies and correlate it themselves.
> No, because covid19-oriented contact tracing requires much more precision than what can be provided by any location data that the operators can trace through their cellular networks; location data are unsuitable to determine a one-time contact with accuracy […] (the other reason is that this approach allows you to trace contacts even if the cellular and/or GPS connectivity is unavailable, 

Yes, exactly. The other interesting thing about the BTLE protocols being proposed is that they’re being designed to report that you came into close proximity to a person of interest, but not (depending on details) where, exactly when, etc. This, plus requiring you to explicitly release your tracking information, is the sense in which they’re “privacy preserving” - implementing minimum semantics needed for this specific purpose and no more.

Of course, one could always cross-correlate with other information (eg, cell-tower-trianguation-level location tracking) to peel some of this back. But if you’re worried about that, the next observation is that the BTLE protocols work even if your LTE radio is turned off - they remember things for later. So you can, at least conceptually, carry your phone with the wide area radio off when you want to, and still learn retrospectively that you were in proximity to a contact.