privacy-preserving publication of user locations in the proximity of sensitive sites bharath...
DESCRIPTION
3 Attack Attack: Associate a site s with fewer than K users Attack is successful in the previous slide:TRANSCRIPT
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Privacy-Preserving Publication of User Locations in the Proximity of Sensitive Sites
Bharath KrishnamachariGabriel GhinitaPanos Kalnis
National University of Singapore
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Privacy Threat
u2
u3
u1
u4
u5
u1EXPOSED
Location Publishing• Traffic congestion control• Infrastructure planning• Snapshot at 2pm
h
Hospital Data (external)
Hu et al., “Privacy Aware Location Publishing for Moving Clients”
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AttackAttack: Associate a site s with fewer than K users
Attack is successful in the previous slide:<u1, h>
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Solution Outline (K-anonymity)
u2u3
u1
u4
u5
s1
s2
ASR3,4
ASR1,5
Attack, K=2<u1, s1><u5, s1><u3, s2><u4, s2>
NOT successful
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Problem Statement User set U, sensitive sites set S Mapping M:S -> 2U
Minimize Generalization Cost (GGC)
Ss
sMsMBRAreaMGGC )))(}({()(
)()(,,|)(|,
2121 sMsMSssKsMSs
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Related work: Query Privacy in LBS Relies on Spatial K-anonymity as well
Gedik & Liu, ICDCS ’05 Mokbel et al., VLDB ’06 Kalnis et al., TKDE ’07 …
But anonymizes a single query Equivalent to |S|=1
In our problem |S|>>1 More difficult to solve
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Related work: “Local” algorithm
u
s1
s4
s3
s2
DE1 DE2
DN1
DS1
DW1
[HXD+07] Hu H., Xu J., Du J., Ng J.K.Y., “Privacy Aware Location Publishing for Moving Clients”, TR, Hong Kong Baptist Univ., 2007www.comp.hkbu.edu.hk/~haibo/privacy_join.pdf
Benefit:NumOfSites/Area
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Drawback of Local’s Publication Format
2-by-2 publishing
Local
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Our ApproachMK: Monochromatic K-anonymity
Phase 1: Transform user locations to 1D Anonymization w.r.t. user set U ONLY Linear algorithm*, 1-D optimal User groups independent of sites S
Phase 2: Assign each anonymous group to nearest site Resolve potential conflicts
E.g., choose assignment with minimum enlargement Repeat until all sites are covered
[GKKM07] Ghinita G., Karras P., Kalnis P., Mamoulis N. “Fast Data Anonymization with Low Information Loss”. In Proc. of VLDB 2007
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MK Example
2D -> 1D
G3G2G1
G2
Output (s1,G1), (s3,G3)
Output (s2,G2)
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Our ApproachBK: Bichromatic K-anonymity
Properties of optimal mapping in 1-D1. Each ASR/group has exactly K users2. ASRs have consecutive users in 1-D order3. Groups do not overlap in 1-D order
Bichromatic clustering of U and S Each cluster has 1 site and K users DP algorithm, linear in K and |U|
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BK Example
Allowable start values for sj
min{Cost[i-1][j], Cost[i-K][j-1]+GC(ui,…,ui+K-1,sj)}
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Experimental Evaluation Naïve competitor: K-Nearest-Neighbors NA Dataset (569120 locations)
U and S randomly sampled from NA Performance metrics:
Anonymization overhead (CPU time) Generalization Cost
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Comparison with “Local”
N=10,000 Users
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Variable number of sites
N=569,120 Users
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Variable K
N=569,120 Users
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Points to Remember Publication of user locations in the proximity
of sensitive sites More difficult than Query-privacy in LBS
“Local” algorithm Very Slow Bad quality, if a secure publishing format is used
Naïve KNN Also slow
Our algorithms: MK, BK Fast & Accurate
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Bibliography on LBS Privacy
http://anonym.comp.nus.edu.sg