  Mobile devices with rich features can record videos, traffic parameters or
air quality readings along user trajectories. Although such data may be
valuable, users are seldom rewarded for collecting them. Emerging digital
marketplaces allow owners to advertise their data to interested buyers. We
focus on geo-marketplaces, where buyers search data based on geo-tags. Such
marketplaces present significant challenges. First, if owners upload data with
revealed geo-tags, they expose themselves to serious privacy risks. Second,
owners must be accountable for advertised data, and must not be allowed to
subsequently alter geo-tags. Third, such a system may be vulnerable to
intensive spam activities, where dishonest owners flood the system with fake
advertisements. We propose a geo-marketplace that addresses all these concerns.
We employ searchable encryption, digital commitments, and blockchain to protect
the location privacy of owners while at the same time incorporating
accountability and spam-resilience mechanisms. We implement a prototype with
two alternative designs that obtain distinct trade-offs between trust
assumptions and performance. Our experiments on real location data show that
one can achieve the above design goals with practical performance and
reasonable financial overhead.
