Privacy Management for

J. Alex Halderman Brent WatersEdward W. Felten

Princeton UniversityDepartment of Computer Science

Portable Recording Devices

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Camera Phones

170 million in 2004

= +× 170 million

=New

PrivacyThreats

Ubiquitous

Recording

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New Privacy Threats

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A Breakdown of Social Norms

Augment them, don’t replace them

Previous Approaches

Law/Policy

Usage RestrictionsLocal Bans

TechnologySignal from beacon disables recording

features

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Based on location, not full context Decide before recording, not

playback

Coarse-Grained Restrictions

Our Approach

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Privacy protection built intotrusted recording devices

Our Approach

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Recording subjects control useNegotiate using their

devices (assume discovery method)

Defers privacy decision to last possible moment

Our Approach

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Encrypt recording before storing

Key share retained by privacy stakeholders

Must ask permission to decrypt

Our Privacy Requirements

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1. Unanimous Consent2. Confidentiality of Vetoes

Colluder

Our Applications

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Laptops/WiFiAOL Instant Messenger

• Protects audio recordings

• Manual discovery

• Protects chat logs • Discovery handled by

AIM

Alice and Bob tell Carol kAlice kBob without revealing other

informationabout kAlice or kBob to anyone

Variation on Chaum’s “Dining Cryptographers”

Secure XOR

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BobAlicekBob SecretSecret kAlice

Carol

A & B choose and exchange random blinding factorsA & B each XOR both blinding factors with their secret input

and send the result to CarolCarol XORs these messages to learn kAlice kBob

BobAlicekBob SecretSecret kAlice

Secure XOR

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BBob Blinding factorBlinding factor BAliceBBob BAlice

kAlice BBob BAlice BBob BAlice kBob

CarolkAlice BBob BAlice BBob BAlice kBob

= kAlice kBob

Carol does not learn kAlice or kBob

Private Storage Protocol

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“Create” Operation

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Identify stakeholders

Need a trusted recording device for

now

Private Storage Protocol

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“Create” Operation

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Choose random keyshares

k1=0110100k2=1011101

Securely tell recorder k1 k2

Secure XOR

k1 k2=1101001

Encrypt using k1 k2 as key

key=1101001

Recorder discards plaintext, keyStakeholders hold on to shares

id=2100624 owners=Alice,BobkAlice=0110100

Secure XOR

Private Storage Protocol

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“Decrypt” Operation

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id=2100624 owners=Bob,AlicekBob=1011101

id=2100624owners=Alice,Bob

Requestor sends request

May we decrypt <2100624>?

Cryptography provides strong protection

Stakeholders apply policies

Secure XOR

To grant, input keyshare into XOR

key=1101001 ?

To deny, give random input to XOR

1110001key=1000101 ?

Vetoes remain confidential

Private Storage Protocol

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“Create”

Location Service

Storage

Recorder BRecorder A

Data In Data In

PersistentAgent A

PersistentAgent B

Player

Agent A Agent B

Keyshare Keyshare

En

cryp

ted

Reco

rdin

g

“Decrypt”

Policy Policy

Data Out

Privacy in Practice

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A Problem of Compliance

Community of like-minded people:Social pressures, local policies, etc.

Privacy law can provide further incentives

Convince manufacturers to build it in:Regulatory pressure, customer demand

Conclusions

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Ubiquitous recording

brings privacy threats

Technology can give control

back to recording subjects

Widespread compliance among like-minded groups

Privacy Management for

J. Alex Halderman Brent WatersEdward W. Felten

Princeton UniversityDepartment of Computer Science

Portable Recording Devices