CS 590S Class Paper Querying Private Data in MovingObject Environments

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CS 590S Class PaperQuerying Private Data in
Moving-Object Environments

• Reynold Cheng
• Department of Computer Science
• ckcheng_at_cs.purdue.edu

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Location-Based Services
Service Provider
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Non-Anonymous Applications

• When I enter the CS building, notify my project
  groupmates
• Tell me the information of my friends who are
  closest to me
• Send (identity, location) to service provider

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Linkability Location Privacy

• A persons identity has high linkability with
  her current location
• She may not want to reveal she is in that
  location (a sensitive area like hospital)
• Location privacy is lost

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Protecting Location Privacy

• Reduce linkability between identity and location
• By injecting spatial uncertainty
• Called location cloaking

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Location Cloaking
true location
region seen by service provider
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Location Cloaking Model
Location cloaking uncertainty region pdf
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Effectiveness of Cloaking

• Location privacy affected by
• Size of uncertainty region
• Fraction of sensitive areas covered by
  uncertainty region
• Information leak (entropy) of uncertainty pdf

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Location Cloaking Service Quality

• Cloaking protects location privacy
• More uncertainty, more privacy
• Service quality may drop
• Lowering spatial accuracy increases ambiguity
• Cloaking agent to handle these problems

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Cloaking Agent System Design
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Related Questions

• How to process cloaked locations?
• Can service quality be quantified?
• Case Study Moving Range Queries
• Return names of all people whom I know, within a
  radius of r units from me

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Imprecise Moving Range Queries

• Moving
• Range Query

Imprecise Moving Range Query

• Inexact answer (S2, 0.1, S3, 0.5, S4, 0.9)
• Quality Score measures answer ambiguity
• Details in paper

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Trajectory Tracing and Linkability
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Protecting Linkability
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Conclusions

• Location cloaking for location privacy
• A framework to relate privacy, cloaking and
  service quality
• Apply the framework to moving range queries
• Solve the problem of trajectory tracing attack by
  patching and delaying

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References

• A. Beresford and F. Stajano. Location Privacy in
  Pervasive Computing. IEEE Pervasive Computing,
  2(1)46-55, 2003.
• R. Cheng, D. Kalashnikov and S. Prabhakar.
  Evaluating Probabilistic Queries over Imprecise
  Data. In Proc. of ACM SIGMOD, June 2003.
• M. Gruteser and D. Grunwald. Anonymous Usage of
  Location-based Services through Spatial and
  Temporal Cloaking. In Proc. of the 1st Intl.
  Conf. on Mobile Systems, Applications and
  Services, May 2003.