If I understand correctly, it's up to every infected person to manually click "upload" (edit: here was "who I was close to", but it's not correct, see note 1 he

If I understand correctly, it's up to every infected person to manually click "upload" (edit: here was "who I was close to", but it's not correct, see note 1 here) once he gets diagnosed, i.e. completely voluntary. That is so that once one is diagnosed others can check if they were close to that one (and when?). And even these lists aren't supposed to be any typical metadata but something that stays local and the third parties can't reconstruct. The idea is, again if I understood, that those who remain negative never have to upload anything that gives any traceable information about them. See my other post here with other relevant quotes from the specification. ---- Edit: 1) Actually what is uploaded is: "the Daily Tracing Keys for days where the user could have been affected" "Upon a positive test of a user for COVID-19, their Diagnosis Keys and associated DayNumbers are uploaded to the Diagnosis Server. A Diagnosis Server is a server that aggregates the Diagnosis Keys from the users who tested positive and distributes them to all the user clients who are using contact tracing." The matching is done locally on every device: "In order to identify any exposures, each client frequently fetches the list of Diagnosis Keys. Since Diagnosis Keys are sets of Daily Tracing Keys with their associated Day Numbers, each of the clients are able to re-derive the sequence of Rolling Proximity Identifiers that were advertised over Bluetooth from the users who tested positive. In order to do so, they use each of the Diagnosis Keys with the function defined to derive the Rolling Proximity Identifier. For each of the derived identifiers, they match it against the sequence they have found through Bluetooth scanning."