Transcript wpes2004.ppt

Privacy Management for
Portable Recording Devices
J. Alex Halderman Brent Waters
Edward W. Felten
Princeton University
Department of Computer Science
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Camera Phones
× 170 million
=
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New
Ubiquitous
= + Privacy
Recording
Threats
170 million in 2004
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New Privacy Threats
A Breakdown of Social Norms
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Previous Approaches
Coarse-Grained Restrictions
Law/Policy
Technology
Signal
from
beacon disables

Based on location, not
full
context
Usage Restrictions
Augment
them, don’t replace
them
recording features
 Local
Decide
Bans before recording, not playback
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Our Approach
Privacy protection built into
trusted recording devices
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Our Approach
Recording subjects control use
Negotiate using their devices
(assume discovery method)
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Our Approach
Encrypt
before
storing
Must
askrecording
permission
to decrypt
Key
share
retained
by privacy
Defers
privacy
decision
to last
stakeholders
possible moment
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Our Privacy Requirements
1. Unanimous Consent
2. Confidentiality of Vetoes
Colluder
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Our Applications
Laptops/WiFi
• Protects
audio recordings
• Manual discovery
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AOL •Instant
Messenger
Protects chat
logs
• Discovery handled by AIM
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Secure XOR
Alice
Bob
kBob Secret
Secret kAlice
Alice and Bob tell Carol kAlice  kBob
without revealing other information
about kAlice or kBob to anyone
Carol
Variation on Chaum’s “Dining Cryptographers”
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Secure XOR
Alice
Bob
kBob Secret
Secret kAlice
BBob Blinding factor
Blinding factor BAlice
BBob
BAlice
BBob  BAlice  kBob
kAlice  BBob  BAlice
Carol
kAlice  BBob  BAlice  BBob  BAlice  kBob
= kAlice  kBob
A & B each XOR both blinding factors with their secret input
Carolthese
does
not learn
kAlice
orblinding
kkBob
A Carol
& B choose
and
exchange
random
XORs
messages
to
learn
kBob
Alice  factors
and
send
the
result
to
Carol
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Private Storage Protocol
“Create” Operation
Need a trusted recording
device for now
Identify stakeholders
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Private Storage Protocol
k1key=1101001
k2=1101001
“Create” Operation
k1=0110100
k2=1011101
Secure XOR
Encrypt
k1 plaintext,

k2
Recorder
discards
key
Securely
tell
recorder
key
k2
Stakeholders
Chooseusing
random
hold
on
keyshares
tok1as
shares
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Private Storage Protocol

“Decrypt” Operation
key=1101001
key=1000101 ?
1110001
Secure
XOR protection
Secure
XOR
Cryptography provides
strong
May we decrypt <2100624>?
id=2100624
owners=Alice,Bob
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id=2100624
owners=Alice,Bob
kAlice=0110100
id=2100624
owners=Bob,Alice
kBob=1011101
Requestor
sends
request
To
To deny,
grant,
Stakeholders
Vetoes
give
input
remain
random
keyshare
apply
confidential
input
policies
into
to XOR
XOR
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Private Storage Protocol
Location Service
Data In
Data In
Recorder A
Recorder B
Encrypted Recording
“Create”
Agent A
Agent B
Keyshare
Keyshare
Persistent
Agent A
Policy
Persistent
Agent B
Policy
“Decrypt”
Storage
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Player
Data Out
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Privacy in Practice
A Problem of Compliance
Community of like-minded people:
Social pressures, local policies, etc.
Convince manufacturers to build it in:
Regulatory pressure, customer demand
Privacy law can provide further incentives
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Conclusions
Ubiquitous recording
brings privacy threats
Widespread
compliance among
like-minded groups
Technology can give control
back to recording subjects
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Privacy Management for
Portable Recording Devices
J. Alex Halderman Brent Waters
Edward W. Felten
Princeton University
Department of Computer Science