We analyze the re-identification risks for individual Internet users and the utility provided to advertising companies by the Topics API, i.e. learning the most popular topics and distinguishing between real and random topics. We provide theoretical results dependent only on the API parameters that can be readily applied to evaluate the privacy and utility implications of future API updates, including novel general upper-bounds that account for adversaries with access to unknown, arbitrary side information, the value of the differential privacy parameter ε, and experimental results on real-world data that validate our theoretical model.
Mário S. Alvim,
Natasha Fernandes,
Annabelle McIver,
Gabriel H. Nunes