In mobile wireless networks, third parties can track the location of mobile nodes by monitoring the pseudonyms used for identification. A frequently proposed solution to protect the location privacy of mobile nodes suggests to change pseudonyms in regions called mix zones.
We study the emergence of location privacy with multiple pseudonyms in various conditions. Our results indicate that the placement of mix zones significantly affects the tracking success by the adversary and that selfish behavior dramatically reduces the achievable privacy unless the cost of pseudonyms is high.

[1] J. Freudiger, M. H. Manshaei, J.-P. Hubaux, and D. C. Parkes. On Non-cooperative Location Privacy: A Game-theoretic Analysis. CCS, 2009 [pdf - bib - slides]
[2] J. Freudiger, R. Shokri, and J.-P. Hubaux. On the Optimal Placement of Mix Zones, PETS, 2009 [pdf - bib - slides - simulations]
[3] R. Shokri, J. Freudiger, M. Jadliwala, and J.-P. Hubaux. A Distortion-based Metric for Location Privacy. WPES, 2009 [pdf - bib]
[4] P. Papadimitratos, L. Buttyan, T. Holczer, E. Schoch, J. Freudiger, M. Raya, Z. Ma, F. Kargl, A. Kung, and J.-P. Hubaux. Secure Vehicular Communication Systems: Design and Architecture. IEEE Communications Magazine, 46(11):100-109, 2008 [pdf - bib]
[5] J. Freudiger, M. Raya, M. Felegyhazi, P. Papadimitratos, and J.-P. Hubaux. Mix-Zones for Location Privacy in Vehicular Networks. WiN-ITS, 2007 [pdf - bib - slides]

Authentication is a required primitive for the majority of security protocols. Hence, our quest for location privacy in upcoming mobile networks also requires to devise mechanisms for untraceable anonymous authentication. Existing anonymous authentication schemes require that mobile nodes coordinate to achieve privacy. For example, with multiple pseudonyms, nodes must coordinate their pseudonym changes in mix zones. With group signatures, the coordination is organized by a central authority. As a consequence, these mechanisms often lack flexibility.
We study the possibility to achieve location privacy in a self-organized way. With this approach, privacy emerges from the mobile network and users gain control over the disclosure of their locations. Our results indicate that self-organized schemes can provide privacy and that mobility increases the achievable anonymity.

[1] J. Freudiger, M. Raya, and J.-P. Hubaux. Self-Organized Location Privacy. Work in progress.
[2] J. Freudiger, M. Raya, and J.-P. Hubaux. Self-Organized Anonymous Authentication in Mobile Ad Hoc Networks. SecureComm, 2009 [pdf - bib - slides]

The emergence of social networks shows that users are eager to share data with friends. We study whether exchanged messages in mobile wireless networks enable third-parties to infer friendships and thus threaten the privacy of mobile users.

Work in progress.

Modern web sites commonly interact with third-party domains to integrate advertisements. Similarly, modern cell phones allow users to share their location to obtain location-based services. In such scenarios, users are in need of a simple way to control the sharing of their information with third parties in order to protect their privacy.
In [2], we propose novel approaches to enable advertisement to have discrimination capabilities without allowing for excessive tracking of users. Intuitively, multiple cookies are maintained in parallel with third-parties to guarantee some privacy. You can test the proposed solution by installing a Firefox extension, Privacookie.

[1] J. Freudiger and J.-P. Hubaux. Privacy amidst Location-based Services. Work in progress.
[2] J. Freudiger, N. Vratonjic, and J.-P. Hubaux. Towards Privacy-Friendly Online Advertisement. W2SP, 2009 [pdf - bib - slides - code]
[3] N. Vratonjic, J. Freudiger, M. Felegyhazi, and J.-P. Hubaux. Securing Online Advertising. Technical report, 2008 [pdf - bib]