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Analyzing the Privacy of Smartphone Apps

Apr 22, 2013

Shah AminiJialiu Lin

Prateek Sachdeva

Jason HongJanne LindqvistNorman Sadeh

Joy Zhang

ComputerHumanInteraction:MobilityPrivacySecurity

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How to Manage Smartphone Privacy?

• Lots of smart devices– 1B smartphones worldwide

• Lots of apps– ~700k apps and 40B+

downloads for each of Android and iOS

• Highly intimate• Lots of rich data• Lots of inferences

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Smartphones are Intimate

Mobile phones and millennials (Pew 2012):• 75% use in bed before going to sleep • 83% sleep with their mobile phones• 90% check first thing in the morning• Half use them while eating • A third use them in the bathroom (!)• A fifth check them every ten minutes

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Smartphone Data is Rich

Who we know(contact list,

social networking)

Who we call(call log)

Who we text(sms log, Kakao,

social networking)

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Smartphone Data is Rich

Where we go(gps, foursquare)

Photos(some geotagged)

Sensors(accel, sound, light)

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Inferences from DataExample: Modeling Social Relationships

• If you were in a jail in Mexico, which of the 500+ “friends” in your phone contact list would come and get you out?

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Inferences from DataExample: Modeling Social Relationships• Can we build a richer augmented

social graph?– models tie strength, group, role

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Inferences from DataExample: Modeling Social Relationships

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Inferences from DataExample: Modeling Social Relationships

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Inferences from DataExample: Modeling Social Relationships

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• Friend or not – 92% accuracy– Using just GPS co-location data

• Life facet {family, social, work} – 90%• Tie strength {low, med, high} – 75%

– Using just contacts, call logs, SMS logs

Cranshaw et al, Bridging the Gap Between Physical Location and Online Social Networks, Ubicomp 2010.

Min et al, Mining Smartphone Data to Classify Life-Facets of Social Relationships, CSCW 2013.

Inferences from DataExample: Modeling Social Relationships

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Sensor dataSleep data

(self-reported ground truth)

Inferences from DataExample: Sleep

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Smartphone Data for DepressionSocial Relationships• Isolation• Lack of close

family or friends

Physical Activities• Mobility• Consistency• Places you go to

Sleep Patterns• Excessive sleep• Too little sleep• Change over time

Cognitive Behaviors• Multitasking• Lots of phone use

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How to Manage Smartphone Privacy?

• Lots of smart devices– 1B smartphones worldwide

• Lots of apps– ~700k apps and 40B+

downloads for each of Android and iOS

• High intimacy• Lots of rich data• Lots of inferences

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Shares your location,gender, unique phone ID,phone# with advertisers

Uploads your entire contact list to their server(including phone #s)

What are your apps really doing?

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Many Smartphone Apps Have “Unusual” Permissions

App Permissions UsedTiny Flashlight + LED Internet Access, phone#

Backgrounds Contact List

Dictionary Location

Bible Quotes Location

• Advertising, malware, bootstrapping social networks, future permissions

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Android

• What do these permissions mean?

• Why does app need this permission?

• When does it usethese permissions?

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Two Threads of Work

• Works in progress, feedback appreciated

• CrowdScanning– Crowdsourcing approach to understand

coarse-grain privacy perceptions of apps

• Gort– Tool for analysts

to understandfine-grain app behaviors

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CrowdScanning Core Ideas

• Idea 1: find the gap between what people expect an app to do and what it actually does

• Idea 2: use crowdsourcing to do this (crowdsource privacy)

Lin et al, Expectation and Purpose: Understanding User’s Mental Models of Mobile App Privacy thru Crowdsourcing. Ubicomp 2012.

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Nissan Maxima Gear Shift

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Privacy as Expectations

• Apply this same idea of mental models for privacy– Compare what people expect an app

to do vs what an app actually does– Emphasize the biggest gaps,

misconceptions that many people had

App Behavior(What an app actually does)

User Expectations(What people think

the app does)

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Crowdsourcing Privacy

• Few people read privacy policies– We want to install the app– Reading policies not part of main task– Complexity of these policies (the pain!!!)– Clear cost (time) for unclear benefit

• Crowdsourcing can mitigate these problems

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10% users were surprised this app wrote contents to their SD card.

25% users were surprised this app sent their approximate location to dictionary.com for searching nearby words.

85% users were surprised this app sent their phone’s unique ID to mobile ads providers.

0% users were surprised this app could control their audio settings.

See all

90% users were surprised this app sent their precise location to mobile ads providers.

95% users were surprised this app sent their approximate location to mobile ads providers.

95% users were surprised this app sent their phone’s unique ID to mobile ads providers.

See all

0% users were surprised this app can control camera flashlight.

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Our Study on App Privacy

• Showed crowd workers screenshots anddescription of app (from Google Play)– 56 of top 100 Android Apps

• Showed permissions one at a time– Only those related to privacy

• Expectation Condition– Why they think the app uses permission– How comfortable they were with it

• Purpose Condition– We gave an explanation (based on our analysis)– How comfortable they were with it

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Our Study on App Privacy

• Participants– Recruited from Mturk, US people only– Asked what version of Android OS they used– Between-subjects (one condition only)

• Method– Only 56 of top 100 apps requested use of

unique phone ID, contact list, or location• Led to a total of 134 app-resource pairs

– 20 participants per pair per condition• 2*20*134 = 5360 tasks

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Results for Location Data (N=20 per app, Expectations Condition)

App Comfort Level (-2 – 2)

Maps 1.52

GasBuddy 1.47

Weather Channel 1.45

Foursquare 0.95

TuneIn Radio 0.60

Evernote 0.15

Angry Birds -0.70

Brightest Flashlight Free -1.15

Toss It -1.2

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Most Unexpected Uses(N=20 per app, Expectations Condition)

• Found strong correlation between expectations & comfort level (r=0.91)

Apps using Contact List Comfort Level (-2 – 2)

Backgrounds HD Wallpaper -1.35

Pandora -0.70

GO Launcher EX -0.75

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Showing Purpose Lowers Concerns

• All differences statistically significant• Big increases for dictionary, Shazam,

Air Control Lite, and others (> 1.0)

App Comfort w/ Purpose

Comfort w/o Purpose

Device ID 0.47 (=0.30) -0.10 (=0.41)

Contact List 0.66 (=0.22) 0.16 (=0.54)

Network Location 0.90 (=0.53) 0.65 (=0.55)

GPS Location 0.72 (=0.62) 0.35 (=0.73)

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Scaling Up CrowdScanning

• It took ~2 wks to crowdsource 56 apps• 700k+ apps for iOS & Android markets

• Idea: Use static & dynamic analysis + clustering for privacy models of apps– Ex. “Games uses location” -1.3– Ex. “Uses location for map” +0.5

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Scaling Up CrowdScanningCrawled Data Set

• Crawled 171k apps from Google Play– App name– Category (Arcade, Finance, etc)– Number of downloads– Average user rating (1-5)– Rating distribution– Price– Content Rating– 13M user reviews

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Scaling Up CrowdScanningStatic Analysis of Apps

• Starting assumptions:– Most apps use third-party libraries– When sensitive data is used, b/c libraries

• Ex. Location sent to ad server via library• Ex. Location sent to Google for maps

• Understanding what libraries app uses and how they are used can offer us richer semantics and explanations

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Scaling Up CrowdScanningLibraries are Major Point of Leverage

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Scaling Up CrowdScanningStatic Analysis of Apps

• Features extracted:– Libraries used– Network conn (in library or in main code)– Permissions (in library or main code)

• 124k apps processed– Uses PyDev (Python for Eclipse) and

AndroGuard (reverse eng apps)– 5 Amazon EC2 instances, 30 secs / app

• Will crowdsource core set of 400 apps and build models to predict privacy

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Scaling Up CrowdScanningTangent: Analyzing App Comments• Linear regression of most common

words to 5-star ratings– Out of 1M comments, 8% of dataset– Only 0.09% comments related to privacy

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Two Threads of Work

• CrowdScanning– Crowdsourcing approach to understand

coarse-grain privacy perceptions of apps

• Gort– Tool for analysts

to understandfine-grain app behaviors

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Gort App Analysis Tool

• Goal of Gort is to help analysts understand and vet behaviors of apps– Journalists– Privacy advocates– Three letter agencies

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Example Comparison

• CrowdScanning: Yelp uses location• Gort: When (what screens) and why?

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Gort v1Control

Flow GraphCurrentScreen

Serverscontacted

HTTPdetails

HTTPrequests

Marketdescription

Permissionsused

Personaldata sent

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Gort v2 Envisioned Workflow

• Start with a pool of apps• Use heuristics to flag unusual behaviors

to direct analyst’s attention– Static and dynamic heuristics

• See overview of apps, view individual apps, check odd behaviors and context (screens)

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Gort v2 Heuristics for Apps

• Interviewed 13 experts– Asked what characteristics and behaviors

they would check to vet an app– Got ~100 heuristics, still organizing them

Network• Sends password

w/o SSL• Connects to

fixed IP address

Permissions• Contact List• Location but not

for maps or ads• Uses mic

Phone / SMS• SMS to fixed /

premium num• Forwards SMS

to server

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Traversing Screens in Apps

• Have to traverse app for some heuristics– Ex. when exactly does the app use location?– Also want to capture screenshots

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Traversing Screens in Apps

• General case is fairly easy– Breadth-first-search from home screen– Uses TEMA to get widgets on screen– Use Android’s MonkeyRunner to simulate

input and get screenshots

• But lots of exception cases…

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Some Hard Cases for Traversal

Dialogs w/side effectsText InputsLogins

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Some Hard Cases for Traversal

Changes tosystem env

AppUpdates

Randomizeddialogs

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Scaling Up CrowdScanningMaking the Results Public

• What will we do with all these results?• Basic idea: deploy a web site

– Let public see results of our scans– Show privacy scores (and explanations)– Tell app developers how to fix their apps

• Awareness, Knowledge, Motivation

• Still early stages here, should have first iteration of site out end of May

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Public Feedback to Date

• Slate• Yahoo News• MSNBC• Pittsburgh Tribune Review

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Thanks!

More info at cmuchimps.orgor email jasonh@cs.cmu.edu

Special thanks to:• Army Research Office• National Science Foundation• Alfred P. Sloan Foundation

• Google• CMU Cylab

Join our community for researchers at:www.reddit.com/r/pervasivecomputing

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The Opportunity

• We are creating a worldwide sensor network with these smartphones

• We can now capture and analyze human behavior at unprecedented fidelity and scale

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Summary

• Smartphones offer big opportunity to understand human behavior at unprecedented fidelity and scale

• Augmented Social Graph• Urban Analytics• CrowdScanning

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Reach of Apps Growing

Finances Automobiles Homes

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Reach of Apps Growing