International Association
for Cryptologic Research

Location tracking accessories (or ``tracking tags'') such as those sold by Apple, Samsung, and Tile, allow owners to track the location of their property and devices via offline tracking networks. The tracking protocols have been designed to ensure some level of user privacy against surveillance by the vendor. Such privacy mechanisms, however, seem to be at odds with the phenomenon of tracker-based stalking, where attackers use these very tags to monitor a target's movements. Numerous such criminal incidents have been reported, and in response, manufacturers have chosen to weaken privacy guarantees in order to allow users to detect malicious stalker tags.

In this work we show how to achieve an improved trade-off between user privacy and stalker detection within the constraints of existing tracking protocols. We implement our new protocol using families of list-decodable error-correcting codes, and give efficient algorithms for stalker detection under realistic conditions.