Explain the relationship between user density, encounters, and tracking ambiguity

Investigate whether increased user density reduces cross-protocol tracking effectiveness because additional encounters create more opportunities for identifier confusion during rotations.

Background

The paper evaluates how environmental factors influence CrossLink’s ability to reconstruct location traces. Its simulations show that privacy leakage decreases as user density increases, but the authors initially attribute this behavior to a conjectured mechanism: denser populations may create more encounters and therefore more ambiguity when devices rotate identifiers.

The authors compare SUMO-based mobility with synthetic random-walk trajectories to examine whether interaction frequency, rather than density alone, explains the observed tracking behavior. Although the experiments provide evidence about this relationship, the passage explicitly presents the causal explanation as a conjecture.

References

We conjectured that this occurs because users have more opportunities to encounter other users, and thus confuse the tracking algorithms when they rotate identifiers.

— CrossLink: Breaking Location Privacy by Linking Device Identifiers Across Protocols  (2609.09963 - Dutta et al., 9 Sep 2026) in Section 6.4, subsection “Evaluation,” Q4: “How do other environmental factors, such as the density of users and the velocity of movement, affect the surveillance performance?”