Random Key Pre-distribution Schemes for Sensor Networks

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Random Key Pre-distribution Schemes for Sensor
Networks

• By
• Arvind Soni

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Outline

• Introduction
• Basic Techniques
• Random Key Pre-distribution
• Q-composite Scheme
• Multi-Path Key Reinforcement
• Random Pair-wise Keys
• Conclusion

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WSNs

• What are WSN?
• Self-organizing set of small battery operated
  sensors, communicating
• via wireless medium.
• Need for security in WSN
• WSNs deployed in hostile environments like battle
  fields.
• Boot-strapping problem in WSN
• Enable a newly deployed sensor network to
  initiate a secure infrastructure.
• Allow legitimate nodes deployed at a later time
  to join securely.

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Boot-strapping (contd)
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Basic Techniques

• Polynomial Based (Bloom et al)
• Pair wise secret key F_a(id_b) F_b(id_a)
• F_a() (F_b()) is the polynomial known to a (b)
• Random Key Pre-distribution (Gilgor et al)
• Location Aware
• Model and use the deployment and topological
  information in combination with the above
  methods.
• Reduces memory over head

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Random Key Pre-distribution

• Initialization
• Assign a set of k-random keys to each node from a
  pool of S keys.
• Shared key discovery
• Each node broadcasts the identifiers of its keys
• The neighboring nodes discover the shared keys
• Path key establishment

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Q-Composite Scheme

• Instead of sharing a single key, the neighboring
  nodes share Q keys and use the hash of the Q keys
  as the shared key.
• Advantage More secure against small-scale node
  capture as compared to the basic scheme.
• Disadvantage Not scalable
• Capture of 50 nodes will lead to compromise of
  1000 links if n10,000!
• Puts a limit on the maximum network size.

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Multi-path Key Reinforcement

• A and B share a secret key Kab
• Assume A knows all the secure disjoint paths to B
  (say r paths) that are h hops or less.
• A sends r random values v1 vr through each of
  the disjoint paths.
• B on receipt of the random values computes the
  common key as
• K Kab xor v1 xor xor vr

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Random Pair-wise Keys

• Generate n unique IDs (n m / p)
• ID1, ID2, ID3, ID4, ID5
• Match each ID with m random IDs
• ID1 -gt ID2, ID4 ID2-gt ID3, ID4 ID3-gt
  ID2,ID5 ID4-gtID1, ID2
• Generate a pair-wise key for each pair of nodes
  and add it to their key ring along with the ID
• Key ring of node1 K12 ID2, K14 ID4

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Advantages of Pair-Wise Method

• Perfect resilience to node capture
• A captured node doesnt reveal any information
  about links its not directly involved with.
• Node to Node identity authentication
• With additional memory and communication overhead
  the scheme can provide distributed node
  revocation and node duplication.
• distributed voting schemes

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Conclusion

• Q-composite scheme improves over basic scheme for
  small scale network attack.
• Multi-path reinforcement improves security at the
  cost of increased communication overhead
• Random pair-wise key scheme provides node-to node
  authentication and perfect resilience to node
  capture
• Combination of these techniques with location
  information and topological information would be
  interesting.
• Effectiveness of the probabilistic schemes in
  actual practical implementation has to be
  experimented.
• Need for other non-probabilistic schemes.