location-based community services (LBCSs)
, the positions of several targets are interrelated. Users can be notified when targets approach or separate from each other. Typical application areas are instant messaging, mobile gaming, dating, fleet management and logistics, as well as child tracking. Finding appropriate anonymization techniques for LBCSs is a hard problem since (i) the targets are continuously monitored and (ii) identifiers of the targets must not change in order to maintain coherence within a community. LBCSs are inherently stateful. Therefore, existing anonymization techniques for
are not suited for LBCSs. In this paper, we present an anonymization technique for LBCSs, which employs distance-preserving coordinate transformations in conjunction with pseudonyms. It is based on the idea that for determining the distance between targets only relative positions are needed. It supports target anonymity, either with respect to the location provider, which collects the position fixes, or the LBS provider. The paper also presents the results of simulations, which we have performed in order to evaluate the proposed mechanism.