Cross Layer Architectures for Wireless Ad Hoc Networks

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Cross Layer Architectures for Wireless Ad Hoc
Networks
PIs Mart Molle, Srikanth V. Krishnamurthy Studen
ts Ioannis Broustis, Arun Saha
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Objectives of this Work

• Specialized capabilities at the physical layer
  can offer enhanced performance.
• Layered approaches fail to effectively exploit
  these capabilities.
• Goals are to design, simulate and implement
  cross-layer architectures that exploit these
  capabilities.
• In particular, we focus on
• Smart antenna-based networking
• Power heterogeneity, and how it affects
  protocols
• UWB-based networking
• How and why to exploit the physical layer to
  support message-based protocols for
  authenticating the location of a node

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Relation to WHYNET

• Because our WHYNET funding is limited, we are
  supporting this work from multiple sources.
• We are also using some of the technologies
  developed from those other efforts.
• We are building a WHYNET testbed with Xbow Motes
  
• Plan to integrate testbed with UCLA via CENIC in
  the next year.

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In this Presentation

• Brief overview of cross-layer techniques for
  solving the proof of location problem in ad hoc
  networks
• Find the physical location of a node, relative to
  its neighbors, without trusting it
• Nodes may be lost, broken or malicious

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Proof-of-Location ProblemBackground Work

• GPS navigation system
• Inverse problem to our question
• One node privately calculates its own position
• Geometry problem is equivalent to ours
• Cellular 9-1-1 service
• Cell towers find location of mobile handset
• Towers have perfect time synchronization, known
  static positions, are all trustworthy

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Previous work on Timed-Echo Protocolsfor
proof-of-proximity problem

• Sastry, et al. combine a radio challenge with an
  ultrasound reply
• Sound is slow enough to measure easily, but easy
  to cheat
• Does not authenticate the identity of the
  respondent
• Waters and Felten use radio for all messages,
  cryptography to secure messages against ID fraud
• Users carry an external tamper-resistant, trusted
  hardware device (i.e.," smart card)
• Processing delay in the smart card is
  significant, but assumed constant and publicly
  known to all participants
• Timing accuracy requirements seem unrealistic

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Previous work related to accurate timing
measurements

• Kennell and Jamieson used timed
  challenge-response to verify the configuration of
  a remote computer
• How do I guard against being misrouted to an
  imposter?
• Brumley and Boneh steal a servers private
  encryption key one bit at a time by measuring the
  response time to a sequence of queries
• Decryption algorithm is iterative, like long
  division
• Some iterations are skipped if data and key are
  related
• Both schemes assume only millisecond timing
  accuracy
• Equivalent to distance error of LA to Santa
  Barbara
• Pasxtor and Veitch developed exotic GPS-enhanced
  network timing equipment to measure 1-way network
  delays
• Testing showed significant differences between
  actual and intended transmit time by a host
• 0.5 ms for real-time OS, gt10 ms for standard
  Linux-based system

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Our Work Use cross-layer support from Physical
Layer to resolve problems not fixable at Layer 2

• Man-in-the-Middle attacks
• Detect an intruder who inserts himself between
  nodes
• Proxy attacks
• Detect a cheater who wants to hide his absence
  from the assigned post by relaying his messages
  through a dumb relay at that location

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Distance/Timing measurements2 frequencies,
GPS-like geometry
C
A
B
D
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Principle of inter-linked challenges

• Challenge K carries data needed to compute an
  offline response to challenge K1
• Response info is cached at the physical layer
  transceiver before challenge K1 arrives
• Actual reply message is generated by the physical
  layer and transmitted immediately
• Simple bit-wise XOR of cached response info with
  incoming challenge

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Principle of partial response

• Man-in-the-Middle cannot benefit from relaying
  challenges and responses between bonafide nodes
• Each node pair generates a unique session key
• Reply message contains a small number of randomly
  chosen bits from the full response, chosen via
  the session key
• MiM will receive useless bits from response

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Challenge-Response Timing Diagram
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Cheat-Resistant Features of our Approach

• Cross-layer generation of response messages
  prevents a cheater from starting its early, or
  transmitting at a slightly higher data rate to
  send the message in less time
• Important because time stamps are based on the
  end-of-message-reception event, not
  start-of-reception
• Cant be hurried because next bit of the reply
  cannot be generated until the corresponding bit
  of new challenge is received
• Partial-response stops a man-in-the-middle
• Even by knowing and relaying the challenge, he
  gets only a useless (for him) the response

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Future Work

• Implementation using Motes or 802.11
• Robust solution of the geometrical problem
• How to handle measurement errors?
• Kalman filtering
• Byzantine algorithms to handle failures