Privacy analysis of FLoC (Mozilla blog)

Over on the Mozilla blog, Eric Rescorla looksinto some of the privacy implications of the Federated Learning of Cohorts(FLoC), which is a Google effort to replacethird-party cookies with a different type of identifier that is lesstrackable. But less tracking does not equal no tracking. "People'sinterests aren't constant and neither are their FLoC IDs. Currently, FLoCIDs seem to be recomputed every week or so. This means that if a tracker isable to use other information to link up user visits over time, they canuse the combination of FLoC IDs in week 1, week 2, etc. to distinguishindividual users. This is a particular concern because it works even withmodern anti-tracking mechanisms such as Firefox's TotalCookie Protection (TCP). TCP is intended to prevent trackers from correlating visits acrosssites but not multiple visits to one site. FLoC restores cross-sitetracking even if users have TCP enabled."