Download Differential Triangulation Attack

Preserving Caller Anonymity in
Voice-over-IP Networks
Mudhakar Srivatsa, Ling Liu
and Arun Iyengar
Presenter: Bo Wu
Agenda
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Voice-over-IP
Caller Anonymity
Threat Models
Defending Methods
Experimental Evaluation
Conclusion
Phone. The history…
PSTN
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PSTN- stands for
Public Switched
Telephone Network
Circuit-based
means reserving
resources for each
user
Kind of expensive
Voice-over-IP: another choice
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Voice over Internet Protocol
“A method for taking analog audio signals, like
the kind you hear when you talk on the phone,
and turning them into digital data that can be
transmitted over the Internet. “
Also known as:
•
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Voice over Packet (VoP)
IP Telephony (IPT)
Benefits
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#1. SAVING MONEY!
• Routing phone calls over
•
existing data networks to
avoid the need for
separate voice and data
networks.
VOIP offer features and
services for free (or at
little cost)
Benefits
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Increased Agility
Tactical Advantages
Integrate things like: emails, phone,
instant messages, etc.
VoIP is popular
Characteristics of VoIP network
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P2P topology
peer
Internet
peer
peer
peer
peer
Characteristics of VoIP network
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Additional QoS requirement
• ITU (International Telecommunication
Union) recommends up to 250ms one-way
latency for interactive voice communication.
People go mad
due to bad
quality
Anonymity in VoIP networks
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What is anonymity?
• NO leakage of
information about
identity
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Why is it important?
• Human rights
• Sensitive applications
Where is the caller?
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Source privacy
Hot topic in many
kinds of networks: Ad
hoc, Sensor networks,
Mesh networks, ……
Papers published in:
Infocom, ICDCS, CCS,
Securecomm, S&P…
What’s the difficulties?
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Strong ability of attackers
• Content analysis
• Timing analysis
Fully distributed
Link latency
……
How VoIP works?
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Establish routes:
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Sending messages
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Confidentiality
• Unstable topology
• Routes across different ASPs
• Comply to different application protocols
• Hop-by-hop encryption
• End-to-end encryption
Establishing routes
InitSearch:
Zhenhua
Bo
<SearchID, dest ID, start time>
How does it work?
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ProcessSearch
Zhenhua
Bo
How does it work?
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FinSearch
Zhenhua
Bo
What’s the problem?
Bad guys are there…
Zhenhua
Bad guy:
Mr. Y
Bad guy:
Mr. X
Bo
What’s the problem?
Bad guys are there…
Zhenhua
Bad guy:
Mr. Y
Bad guy:
Mr. X
Bo
What’s the problem?
What if Zhenhua is
surrounded by bad guys?
Bad guy:
Mr. W
Zhenhua
Bad guy:
Mr. Y
Bad guy:
Mr. Z
Bo
Bad guy:
Mr. X
Threat model
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Composed by assumptions and
formulations
Three threat models:
• Deterministic Triangulation Attack
• Statistical Triangulation Attack
• Differential Triangulation Attack
Deterministic Triangulation Attack
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“Deterministic” means fixed latency for
each link
Exploit two properties of the route set up
protocol:
• 1. It establishes the shortest route between the
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two nodes src and dst.
2. Any node can estimate its distance from src
=> Each bad guy has the knowledge of its
distance from any other node in the network
Deterministic Triangulation Attack
Mr. Y
Bo
Mr. X
Deterministic Triangulation Attack
Deterministic Triangulation Attack
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For each bad guy pi in network
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Calculate the final score:
• If
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Statistical Triangulation Attack
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“Statistical” means link latency follows some
probabilistic distribution, say Gaussian
distribution
Exploit one nice property of Gaussian
distribution
• X, Y follow Gaussian distribution
• If Z = X + Y THEN E(Z) = E(X)+E(Y)
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When calculating scores, use mean value
Differential Triangulation Attack
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The mentioned two attacks relies on
the time stamp in search packet to
make the first estimation.
What if the source remove time stamp?
• The attackers can still cooperate……
Differential Triangulation Attack
Zhenhua
Mr. Y
Bo
Mr. Y
Dist(Bo, X)-Dist(Bo,Y) < Dist(Zhenhua, X)-Dist(Zhenhua, Y)
Topology discovery
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All of the three threat
models require global
information like topology
and link latency
Malicious nodes can
collude to collect such
information
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Send ping messages with
small TTL
Infer local topology and
link latency through pong
messages
Attack efficiency
Deterministic Triangulation
Statistical Triangulation
Attack efficiency
Differential Triangulation
Defending algorithms
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General idea: break the tight
correlation of timing and distance
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Random walk Search Algorithm
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Hybrid route set up
• Best anonymity, worst QOS
• Tradeoff between anonymity and QOS
Random walk search algorithm
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Basic idea:
• Randomly select a neighbor to forward
search request instead of broadcasting
(Random walk is used in tens of papers to
defend against traffic analysis.)
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Why it works?
• According to random walk theory:
Hybrid Route set up protocol
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Controlled random walk
• Two phases
• Random walk search phase
• Search dest node by random walk
• Broadcast search phase
• Search dest node by broadcast
• One kind of probabilistic routing:
• Start at random walk search phase
• Remain in this phase with probability of p
• Transfer to Braodcast search phase with probability
of 1-p
Hybrid Route set up protocol
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Multi-Agent Random Walk
• Send out w search messages instead of one
• Every search message performs random walk
• Route established when the first search message
arrives at dest node
• Tradeoff when setting w
• Bigger w means smaller latency
• Bigger w also increases attacking efficiency
Simulation results
Latency study:
Simulation results
Anonymity study:
Comments
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Brilliant Threat models
• Capture key properties of broadcast
• A small percentage of nodes can attack
very accurately
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Not quite novel defending methods
• Random walk has been used by tens of (if
not hundreds of) papers
• No deep analysis of the performance
Conclusion
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VoIP is gaining more and more
popularity
Three threat models directly target
at caller’s anonymity
Introduce randomness to defend
against timing attack
Lesson: challenging problem to protect
privacy as well as providing QoS
 Questions?