sddr: light-weight, secure mobile encounters
TRANSCRIPT
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SDDR: Light-Weight, Secure Mobile Encounters
Matthew Lentz, Viktor Erdélyi, Paarijaat Aditya!Elaine Shi, Peter Druschel, Bobby Bhattacharjee
University of Maryland Max Planck Institute for Software Systems
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Mobile Social Applications
Services based on user context:
1 location activity nearby peers2 3
Latitude FireChat
Foursquare Haggle
Highlight
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//
Common: Centralized Service
Service
Involves a trusted third party
UI+Sensors
UI+Sensors
//
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Alternate: Device-to-Device
Service
Service
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Alternate: Device-to-Device
Enables tracking by adversaries
Service
Service
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Alternate: Device-to-Device
Enables tracking by adversaries
Service
Service
13
5B
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13
5B
Alternate: Device-to-Device
Enables tracking by adversaries
Service
Service
GIZMODO - “Brave New Garbage: London’s Trash!Cans Track You Using Your Smartphone” (2013)
Credit: http://gizmodo.com/brave-new-garbage-londons-trash-cans-track-you-using-1071610114
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Randomize Addresses?
13
5B
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Randomize Addresses?
?
? 47
6B
Unlinkable, but does not support recognition!
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Secure Device Discovery!and Recognition
1
2
3
Secure Encounter Primitive
Strawman Protocol
System Goals and SDDR Protocol
4 Evaluation and Concurrent Work
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Secure Encounters
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Secure Encounters
Establish a Shared Key
Secure communication through untrusted channel!(e.g., pseudonymous email)
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Secure Encounters
Establish a Shared Key
Secure communication through untrusted channel!(e.g., pseudonymous email)
Unlinkable by default { , }?
? ?
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Recognition
Want to recognize each other in encounters
Encounters
{ , }?
Encounters
{ , }?
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Recognition
Want to recognize each other in encounters
… while remaining unlinkable by others
Encounters
{ , }?
Encounters
{ , }?
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Recognition
Want to recognize each other in encounters
Encounters
{ , }?
Encounters
{ , }?
Map ephemeral pseudonyms to long-lived identities { , }{ , }
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Revocation and Scoping
#&@$!
No Longer Friends
Temporary Friends
USENIX Allow recognizability by friends using context-based constraints
Context-based Scoping
B
Only At Work
Only After 8pm
A C
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Revocation and Scoping
#&@$!
No Longer Friends
Temporary Friends
USENIX Allow recognizability by friends using context-based constraints
Context-based Scoping
B
Only At Work
Only After 8pm
A C
Efficient and unilateral revocation is required
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Security Properties
Discover devices while preserving user privacy
Recognize peers with prior trust relations and support efficient, unilateral revocation
Secure communication between encounter peers
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Threat Model
Trust OS and apps on your phone
No PHY layer attacks considered
Participate with all nearby devices (arbitrary subset of colluding attackers)
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Enabling Recognition
Agree on a shared secret “link value”
Encounters
{ , }?
Encounters
{ , }?
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Enabling Recognition
Agree on a shared secret “link value”
Encounters
{ , }?
Encounters
{ , }?
= H( )
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Recognition and Revocation
Advert ListenAdvert Listen
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Recognition and Revocation
Advert
“I allow and to recognize me”
ListenAdvert Listen
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Recognition and Revocation
Advert
“I allow and to recognize me”
Listen
“I want to recognize ”
Advert Listen
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Recognition and Revocation
Advert ListenAdvert Listen
“I revoke ’s right to recognize me”
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Recognition and Revocation
Advert ListenAdvert Listen
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Recognition by Intersecting Sets
Advert ListenAdvert Listen
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Recognition by Intersecting Sets
Advert ListenAdvertListen
U U
= =
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Strawman Protocol
Advert ListenAdvert Listen
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Strawman Protocol
Diffie-Hellman (DH) ExchangeGenerate
Compute
Generate
Compute
Advert ListenAdvert Listen
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Strawman Protocol
Diffie-Hellman (DH) ExchangeGenerate
Compute
Generate
Compute
Private Set Intersection (PSI)
Advert ListenAdvert Listen
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Strawman Protocol
Diffie-Hellman (DH) ExchangeGenerate
Compute
Generate
Compute
Private Set Intersection (PSI)
Advert ListenAdvert Listen
{ , } { , }
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PSI is Prohibitively Slow
1ms
10ms
100ms
1s
10s
1 2 4 8 16 32 64 128 256
Com
puta
tion
Tim
e (lo
g sc
ale)
Size of Advert/Listen Sets (log scale)
PSI (JL10) on Samsung!Galaxy Nexus
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PSI is Prohibitively Slow
1ms
10ms
100ms
1s
10s
1 2 4 8 16 32 64 128 256
Com
puta
tion
Tim
e (lo
g sc
ale)
Size of Advert/Listen Sets (log scale)
PSI (JL10) on Samsung!Galaxy Nexus
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System Goals
Efficiency - Practical for resource-constrained devices
Scalability - Handle many peers (e.g., stadium)
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System Goals
Efficiency - Practical for resource-constrained devices
Scalability - Handle many peers (e.g., stadium)
Need to develop secure protocols with!energy efficiency as a first order goal
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Divide time into discrete epochs, across which user is unlinkable.
SDDR Protocol State
Advert Listen
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SDDR Protocol State
In each epoch, generate:
DH Key Pair1 Bloom Filter2
Advert Listen
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SDDR Protocol State
In each epoch, generate:
DH Key Pair1 Bloom Filter2
Probabilistic set digest for advertised link values
We use them for compactness, not security
Advert Listen
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DH Key Pair1 Bloom Filter2
SDDR Protocol State
In each epoch, generate:Advert Listen
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DH Key Pair1 Bloom Filter2
SDDR Protocol State
In each epoch, generate:Advert Listen
H( Public, )
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DH Key Pair1 Bloom Filter2
SDDR Protocol State
In each epoch, generate:Advert Listen
H( Public, )
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DH Key Pair1 Bloom Filter2
SDDR Protocol State
In each epoch, generate:Advert Listen
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DH Key Pair1 Bloom Filter2
SDDR Protocol State
Random padding to global maximum size
In each epoch, generate:Advert Listen
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DH Key Pair1 Bloom Filter2
SDDR Protocol State
Public
In each epoch, generate:Advert Listen
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DH Key Pair1 Bloom Filter2
SDDR Protocol State
Public
In each epoch, generate:Advert Listen
Device discovery,!recognition, and!
key exchange in a !single message
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SDDR ProtocolPublic Public
Advert ListenAdvert Listen
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SDDR ProtocolPublic Public
Public
Advert ListenAdvert Listen
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SDDR ProtocolPublic Public
Public
Advert ListenAdvert Listen
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SDDR ProtocolPublic Public
Public
Advert ListenAdvert Listen
Locally Compute1
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SDDR ProtocolPublic Public
Public
Advert ListenAdvert Listen
H( Public, )
Locally Compute1
2 Query
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SDDR ProtocolPublic Public
Public
Advert ListenAdvert Listen
H( Public, )
Locally Compute1
2 Query
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Can mitigate false positives (Details in paper)
SDDR ProtocolPublic Public
Public
Advert ListenAdvert Listen
H( Public, )
Locally Compute1
2 Query
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SDDR ProtocolPublic Public
Encounters
{ , }
Advert ListenAdvert Listen
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SDDR ProtocolPublic Public
Encounters
{ , }Encounters
{ , }
Advert ListenAdvert Listen
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SDDR Implementation
Prototype for Android using Bluetooth 2.1
BattOr for Power Measurements
Developed/Evaluated on Samsung Galaxy Nexus
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System Goals
Efficiency - Practical for resource-constrained devices
Scalability - Handle many peers (e.g., stadium)
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1ms
10ms
100ms
1s
10s
1 2 4 8 16 32 64 128 256
Com
puta
tion
Tim
e (lo
g sc
ale)
Size of Advert/Listen Sets (log scale)
PSI (JL10)
SDDR vs PSI - Computation
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1ms
10ms
100ms
1s
10s
1 2 4 8 16 32 64 128 256
Com
puta
tion
Tim
e (lo
g sc
ale)
Size of Advert/Listen Sets (log scale)
PSI (JL10)
SDDR vs PSI - Computation
10µs
100µs
1ms
10ms
100ms
1s
10s
1 2 4 8 16 32 64 128 256
Com
puta
tion
Tim
e (lo
g sc
ale)
Size of Advert/Listen Sets (log scale)
PSI (JL10)SDDR (Pfp = 3.03%)
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1ms
10ms
100ms
1s
10s
1 2 4 8 16 32 64 128 256
Com
puta
tion
Tim
e (lo
g sc
ale)
Size of Advert/Listen Sets (log scale)
PSI (JL10)
SDDR vs PSI - Computation
10µs
100µs
1ms
10ms
100ms
1s
10s
1 2 4 8 16 32 64 128 256
Com
puta
tion
Tim
e (lo
g sc
ale)
Size of Advert/Listen Sets (log scale)
PSI (JL10)SDDR (Pfp = 3.03%)
Faster by over 4!orders of magnitude
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SDDR vs PSI - Power Traces
0
500
1000
1500
2000
0 20 40 60 80 100 120
DH
+PSI
ove
r BT2
.1Po
wer
Con
sum
ed (m
W)
Time (sec)
Discovery RecognitionIncoming
Recognition
0
500
1000
1500
2000SD
DR
ove
r BT2
.1Po
wer
Con
sum
ed (m
W)
Discovery/Recognition
IncomingDiscovery/Recognition
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SDDR vs PSI - Power Traces
0
500
1000
1500
2000
0 20 40 60 80 100 120
DH
+PSI
ove
r BT2
.1Po
wer
Con
sum
ed (m
W)
Time (sec)
Discovery RecognitionIncoming
Recognition
0
500
1000
1500
2000SD
DR
ove
r BT2
.1Po
wer
Con
sum
ed (m
W)
Discovery/Recognition
IncomingDiscovery/Recognition
Nearly invisible footprint within BT discovery
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SDDR vs PSI - Power Traces
0
500
1000
1500
2000
0 20 40 60 80 100 120
DH
+PSI
ove
r BT2
.1Po
wer
Con
sum
ed (m
W)
Time (sec)
Discovery RecognitionIncoming
Recognition
0
500
1000
1500
2000SD
DR
ove
r BT2
.1Po
wer
Con
sum
ed (m
W)
Discovery/Recognition
IncomingDiscovery/Recognition
Nearly invisible footprint within BT discovery
Cheap, non-interactive protocol!enables low-energy implementation
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SDDR Evaluation
Time to Compute Recognizability
Energy Consumption - Power Traces
Energy Consumption - Micro-benchmarks
Battery Life vs. # Nearby Devices
✓✓
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EnCore - Communication PlatformAppeared in MobiSys ‘14
Supports content sharing for groups of socially meaningful
encounters
“Great discussion!” - Amy
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Summary
Mobile social applications have!significant privacy challenges
www.cs.umd.edu/projects/ebn
SDDR provides secure encounter primitive runs efficiently on mobile devices
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SDDR over Bluetooth 2.1
DiscoverableResponds to inquiry scan with address and beacon
InquirerPerforms inquiry scan, receiving and processing nearby devices’ beacons
CPU
BT
Change MAC address each epoch
B
BC