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MobiHide: A Mobile Peer-to-Peer System for Anonymous Location-Based Queries

MobiHide: A Mobile Peer-to-Peer System for Anonymous Location-Based Queries. Gabriel Ghinita, Panos Kalnis, Spiros Skiadopoulos National University of Singapore and University of Peloponnese, Greece. L ocation- B ased S ervices. LBS users Mobile devices with GPS capabilities

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MobiHide: A Mobile Peer-to-Peer System for Anonymous Location-Based Queries

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  1. MobiHide: A Mobile Peer-to-Peer System for Anonymous Location-Based Queries Gabriel Ghinita, Panos Kalnis, Spiros Skiadopoulos National University of Singapore and University of Peloponnese, Greece

  2. Location-Based Services • LBS users • Mobile devices with GPS capabilities • NN and Range Queries • Location server is NOT trusted • Google Maps, Mapquest, Microsoft Live, etc. • Privacy? Anonymity? “Find closest hospital to my present location”

  3. Problem Statement • Hide IP address and username • But user location may disclose identity • Triangulation of device signal • Publicly available databases • Physical surveillance • How to preserve query source anonymity? • Even when exact user locations are known

  4. K-Anonymity [Swe02] Quasi-identifier (a) Microdata (b) Voting Registration List (public) [Swe02] L. Sweeney. k-Anonymity: A Model for Protecting Privacy. Int. J. of Uncertainty, Fuzziness and Knowledge-Based Systems, 10(5):557-570, 2002.

  5. K-Anonymity (cont.) • 2-anonymous microdata (b) Voting Registration List (public)

  6. Anonymizing Spatial Region • Identification probability ≤1/K

  7. Centralized Anonymizer • Intermediate tier between users and LBS Bottleneck and single point of attack/failure

  8. MobiHide – Fully Distributed

  9. Existing Work: CloakP2P [Chow06] • Find K-1 NN of query source • Source likely to be closest to ASR center • Vulnerable to “center-of-ASR” attack NOT SECURE !!! uq 5-ASR [Chow06] – Chow et al, A Peer-to-Peer Spatial Cloaking Algorithm for Anonymous Location-based Services, ACM GIS ’06

  10. Existing Work: PRIVE [GKS07] Aq has the reciprocity property iff • |AS| ≥ K •  ui,uj  AS, ui  ASj uj  ASi [GKS07] – PRIVÉ: Anonymous Location-based Queries in Distributed Mobile Systems , WWW ‘07

  11. PRIVE (cont.) • Based on Hilbert space-filling curve • index users by Hilbert value of location • partition Hilbert sequence into “K-buckets”

  12. PRIVE (cont.) Start End • Based on Hilbert space-filling curve • index users by Hilbert value of location • partition Hilbert sequence into “K-buckets”

  13. PRIVÉ Hierarchical Architecture • But requires “global knowledge” • Global rank of query source required • PRIVÉ employs an annotated tree index

  14. Motivation More secure Faster PRIVE MobiHide CloakP2P

  15. MobiHide • Uses Hilbert transformation • Key Idea • Remove the need for global knowledge • Allow random group formation • Scalable DHT infrastructure employed • Chord DHT

  16. MobiHide: Group Formation K

  17. MobiHide: Example

  18. MobiHide: Privacy • MobiHide is not reciprocal • Privacy guaranty for uniform query distribution only • But offers strong privacy features in practice, even for skewed distribution

  19. Correlation Attack (K = 4) U6 U8 U5 U7 U4 U9 U3 • 4-anonymity not achieved • However: Difficult attack in practice U10 U1 U2

  20. MobiHide Implementation • Two-layer Chord DHT • Each Chord node is a cluster of users • Bounded cluster size [,3)

  21. User Join/Cluster Split

  22. Load Balancing & Fault Tolerance • Load Balancing • Cluster head rotation mechanism • Fault Tolerance • Chord Periodic Stabilization Protocol • Leader election protocol • In case of cluster head failure

  23. Experimental Setup • San Francisco Bay Area road network • Network-based Generator of Moving Objects* • Up to 10000 users • Velocities from 18 to 68 km/h • Uniform and skewed query distribution * T. Brinkhoff. A Framework for Generating Network-Based Moving Objects. Geoinformatica, 6(2):153–180, 2002.

  24. “Center-of-ASR” Attack

  25. Correlation Attack

  26. ASR Formation Latency Response Time (sec)

  27. Points to Remember • LBS Privacy an important concern • Existing solutions are either not secure … • … or not scalable • MobiHide • Privacy guaranty for uniform query workload • Good best-effort privacy for skewed workload • Excellent scalability inherited from Chord DHT

  28. Bibliography on LBS Privacy http://anonym.comp.nus.edu.sg ?

  29. Bibliography • [Chow06] – Mokbel et al, A Peer-to-Peer Spatial Cloaking Algorithm for Anonymous Location-based Services, ACM GIS ’06 • [Gru03] - Gruteser et al, Anonymous Usage of Location-Based Services Through Spatial and Temporal Cloaking, MobiSys 2003 • [GKS07] – Ghinita G., Kalnis P., Skiadopoulos S., PRIVÉ: Anony-mous Location-based Queries in Distributed Mobile Systems, WWW 2007 • [Mok06] – Mokbel et al, The New Casper: Query Processing for Location Services without Compromising Privacy, VLDB 2006

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