©2009 carnegie mellon university : 1 an overview of location privacy for mobile computing jason...

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An Overview of Location Privacy for Mobile Computing

Jason [email protected]

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Ubiquity of Location-Enabled Devices

•2009: 150 million GPS-equipped phones shipped

•2014: 770 million GPS-equipped phones expected to ship (~ 5x increase!)

•Future: Every mobile device will be location-enabled

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[Berg Insight ‘10]

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Location-Based Services Growing

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Lots of Location-Based Services

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Claims over 5 million users

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5Potential Benefits of Location

• Okayness checking• Micro-coordination• Games

– Exploring a city

• Info retrieval / filtering– Ex. geotagging of photos

• Activity recognition– Ex. walking, driving, bus

• Improving trust– Co-locations to infer tie strength and trust

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6Potential Risks

• Little sister• Undesired social obligations• Wrong inferences• Over-monitoring by employers

Failing to address accidents and legitimate concerns could blunt

adoption of a promising technology

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7Protecting Location Privacy

• System architecture– How you get location– Where and how data stored and used

• User interface and policies– When is it shared– How is it displayed

• User studies– How do people manage in practice

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8Protecting Location Privacy




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How You Get and Use Location

• Some location-based content,even if old, still useful

• Different time-to-live

Shah Amini et al, Caché: Caching Location-Enhanced Contentto Improve User Privacy. (Under Review)

Real-time

Daily

Weekly

Monthly

Yearly

Traffic, Parking spots, Friend Finder

Weather, Social events, Coupons

Movie schedules, Ads, Yelp!

Geocaches, Bus schedules

Maps, Store locations, Restaurants

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How You Get and Use Location

• Pre-fetch all the content you might need for a geographic area in advance– SELECT * from DB where City=‘Pittsburgh’

• Then, use it locally on your device only– We assume that you determine your

location locally using WiFi or GPS– So a content provider would only know

you are in Pittsburgh

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Feasibility of Pre-Fetching

• Are people’s mobility patterns regular?– Pre-fetching useful only if we can

predict where people will be– Locaccino: Top 20 of 4000, 460k traces– Place naming: 26 people, 118k traces

• For each person, 5mi radius around two most common places (home + work) accounts for what % of mobility data?

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5mi

Work

Home

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Radius

5mi

10mi

15mi

Locaccino

86%

87%

87%

Place Naming

79%

84%

86%

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• Content doesn’t change that often– Average amount of change per day

(over 5 months)

• Downloading it doesn’t take long– NYC has 250k POI = 100MB, 65MB for map

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Caché Toolkit

• Android background service for apps– Apps modified to make requests to service

– User specifies home and work locations– Caché service pre-fetches content in

background when plugged in and WiFi– Caché also gets content for your

region if you spend night there

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Protecting Location Privacy




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Why People Use Foursquare

• Started in Mar 2009, 5 million users• After two decades of research,

finally a LBS beyond navigation– Large graveyard of location apps– Critical mass of devices and developers

• Opportunity to study value proposition and how people manage privacy

Janne Lindqvist et al, I’m the Mayor of My House: Examining Why People Use a Social-Driven Location Sharing Application, CHI 2011

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What is Foursquare?

• “Foursquare is a mobile application that makes cities easier to use and more interesting to explore. It is a friend-finder, a social city guide and a game that challenges users to experience new things, and rewards them for doing so. Foursquare lets users "check in" to a place when they're there, tell friends where they are and track the history of where they've been and who they've been there with.”

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How Does Foursquare Work?

• Check-in– See list of nearby places– Manually select a place– “Off the grid” option – Can create new places– Facebook + Twitter too

• Can see check-ins of friends, plus who else is at your location

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Leave tips for others

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Earn badges for activities

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Become mayor of a place if youhave most check-ins in past 60 days

Wean Hall http://foursquare.com/venue/209221 Gates http://foursquare.com/venue/174205

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News of the Weird

• People fighting to be mayors of a place– One pair eventually got engaged

• Some people mayor of 30+ places• Some businesses offering discounts to

mayors

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Three-Part Study of Foursquare

• Why do people use foursquare?– How do they manage privacy concerns?– Surprising uses?

• Interviews with early adopters of LBS (N=6)

• First survey to understand range of uses of foursquare (N=18)

• Second survey to understand details of use, especially privacy (N=219)

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Why People Check-In

• Principal components analysis based on survey data– See paper for details

• Foursquare’s mission statement quite accurate– Fun (mayorships, badges)– Keep in touch with friends– Explore a city– Personal history

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Privacy IssuesWhy people don’t check-in

• Presentation of Self issues– Didn’t want to be seen

in McDonalds or fast food– Boring places, or at Doctor’s

• Didn’t want to spam friends– Facebook and Twitter

• Didn’t want to reveal location of home– Tension: “Home” to signal availability– Tension: Some checked-in everywhere

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Privacy Issues

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Privacy Issues

• Surprisingly few concerns about stalkers– Only 9/219 participants (but early adopters)

• Checking in when leaving (safety)– Surprising use, 29 people said they did this– 71 people (32%) used for okayness checking

• Over half of participants had a stranger on their friends list– Want to know where interesting people go– Perceived like Twitter followers– Suggests separating Friends from friends

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Protecting Location Privacy




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Sharing One’s Location

• Place naming– “Hey mom, I am at 55.66N 12.59E.”

vs “Home”

• User study + machine learning to model how people name places– Semantic: business, function, personal– Geographic: city, street, building

Jialiu Lin et al, Modeling People’s Place Naming Preferencesin Location Sharing, Ubicomp 2010

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• Location abstractions

share nothing &

no social benefits

share precise location (GPS) &

max social benefits

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share nothing &

no social benefits

share precise location (GPS) &

max social benefits

use location abstractions to scaffold privacy

concerns

use location abstractions to scaffold privacy

concerns

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type of description example

geographic 100 Art Rooney AveNear Golden TriangleDowntownPittsburgh

semantic Heinz FieldSteelers vs. BengalsSteelers’ homeFootball field

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• Place entropy

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Understanding Human Behavior at Large Scales

• Capabilities of today’s mobile devices– Location, sound, proximity, motion– Call logs, SMS logs, pictures

• We can now analyze real-world social networks and human behaviors at unprecedented fidelity and scale

• 2.8m location sightings of 489 volunteers in Pittsburgh

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• Insert graph here• Describe entropy

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Early Results

• Can predict Facebook friendships based on co-location patterns– 67 different features

• Intensity and Duration• Location diversity (entropy)• Mobility• Specificity (TF-IDF)• Graph structure (mutual neighbors, overlap)

– 92% accuracy in predicting friend/not

Justin Cranshaw et al, Bridging the Gap BetweenPhysical Location and Online Social Networks, Ubicomp 2010

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Using features such a location entropy significantly improves performance over shallow features such as number of co-locations

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Inte

nsity

feat

ures

Inte

nsity

feat

ures

Num

ber

of

co-

loca

t ions

Num

ber

of

co-

loca

t ions

With

out intensit

y

Full model

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Early Results

• Can predict number of friends based on mobility patterns– People who go out often, on weekends,

and to high entropy places tend to have more friends

– (Didn’t check age though)

Justin Cranshaw et al, Bridging the Gap BetweenPhysical Location and Online Social Networks, Ubicomp 2010

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Ongoing Work

• Managing geotagged photos• Enhanced social graph• Understanding real-world human

behavior at large scales

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Managing Geotagged Photos

• 4.3% Flickr photos, 3% YouTube, 1% Craigslist photos geotagged

• Idea: Use place entropy to differentiate between public / private

• But need to radically scale up entropy– 2.8m sightings, 489 volunteers, N years

Wired Magazine story

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Enhanced Social Graph

• Family, friends, co-workers, acquaintances all mixed together

• Gay friends and 12yo swimmers

• Family friends and high school friends

• Friends and boss• My personal use

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Enhanced Social Graph

• Create a more sophisticated graph that captures tie strength and relationship

• Take call data, SMS, FB use, co-locations

• More appropriate sharing

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• What does me going to a placesay about me and that place?

• Scale up to thousands of people, what does it say about people in a city?

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• Utility for individuals– Predict onset of depression– Infer physical decline– Predict personality type

• Utility for groups– Architecture and urban design– Use of public resources (e.g. buses) – Traffic Behavioral Inventory (TBI)– Ride-sharing estimates– What do Pittsburgher’s do?– What do Chinese people in Pittsburgh do?

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• Get location from thousands of people in a city– Or, what if we could give smart phone to every

incoming freshman?

• New metrics to describe people and places– Churn, transience, burst

• Ways of sharing data with other researchers while maintaining privacy of individuals?– Very high cost in collecting data– How to offer k-anonymity (or other) guarantees?– Privacy server rather than sharing data

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Research Angle of Attack

Sensed DataLocation, sound, proximity, motion

Computer DataFacebook, Call Logs,

SMS logs

Intermediate MetricsCharacterize People and Places at Large Scale

Human Phenomena We Care AboutPrivacy, Health Care, Relationships,

Info Overload, Architecture, Urban Design

Privacy M

od

els

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End-User Privacy in HCI

• 137 page article surveying privacy in HCI and CSCW

Iachello and Hong, End-User Privacy in Human-Computer Interaction, Foundations and Trends in Human-Computer

Interaction

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WYEP Summer FestivalBlizzard …same guyTrigger happy guyRandom peak

EventEvent

Non-eventNon-event

2010 Photos in Pittsburgh

©2009 carnegie mellon university : 1 an overview of location privacy for mobile computing jason...

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