1. Key Distribution and Route Selection in Wireless Sensor Networks Nathan Lewis, Noria Foukia {ndlewis,nfoukia}@infoscience.otago.ac.nz Information Science Institute University of Otago Dunedin, New Zealand

2. Objectives Efficiency of distribution of pair-wise encryption keys Reliability of route selection

3. Overview Key Distribution – Trust – Neighbor-based key distribution Route Selection – Trust and Cost – Expenditure Avoiding Loops – Testing routes

4. Key Distribution By Base Station – All keys created by the Base Station – Nodes must communicate with the Base Station to receive pair-wise keys – Nodes may be many hops from the Base Station

5. Key Distribution By Neighbor – Common trusted neighbor can create a key – Initial trust calculation – Communications savings

6. Number of transmissions/node required for all nodes to acquire pair-wise keys with their immediate neighbors.

7. Route Selection Trust and Cost – Route Trust (TR) is the minimum of the trust values that each node has for the next hop on the route – Route Cost (CR) is the sum of the costs of each hop to the destination – TR A→B →BS = min(TN A →B, TR B →BS ) CR A →B →BS = CN A →B + CR B →BS

8. Route Selection Expenditure – How much we expect to pay to use a given route – E A = CR A + (1 – TR A )CR B CR A is the cost to use route A (1 – TR A ) is the probability of route A failing CR B is the cost to use route B – E B = CR B + (1 – TR B )CR A Compare two routes – Calculate E A and E B and select route with smaller Expenditure Multiple routes (C, D,...)

9. Avoiding Loops Loss of route information messages – Inconsistent picture of the state of the neighborhood – Possibility of selecting route that causes a loop First send route test message – If message is received at destination then route does not contain loop – If message returns to sender then sender knows a loop exists and can avoid using that route

10. Summary Neighbor-based pair-wise key distribution reduces communications with large numbers of nodes Route selection requires only local information, has simple calculation and only requires a single pass through the list of available routes Reliable method of avoiding loops

11. Future work May not need to test whole route, limit number of hops Add a reputation mechanism Test in environment where nodes are mobile Test in hostile environment with hostile nodes  nfoukia@infoscience.otago.ac.nz