A Key Management Scheme for Wireless Sensor Networks Using Presenter Todd Fielder Deployment Knowledge Key Agreement Schemes Trusted Server Self Enforcing Requires trusted infrastructure Asymmetric cryptography Pre Distribution Key information is pre distributed prior to deployment In sensor networks only a small portion of the keys are predistributed Key Pre distribution Use only a subset of keys within the network and probabilistically guarantee a connected graph dependent on node density Not all nodes will be connected Possible to increase this probability and connected nodes if deployment knowledge is used Nodes will be deployed in some order i e there is a higher probability that a node deployed at time t we be closer to other nodes deployed at time t than to nodes deployed at time t 1 Definitions and Assumptions Static Nodes Deployment is evenly distributed through region Is this a safe assumption Deployment Point Point location where a node may be deployed May reside in an area around deployment point which is defined by a probability density function pdf i e the helicopter where the node is dropped from Resident Point Point near the deployment point where sensor actually resides i e where the node lands Group Based Deployment Model Group of sensors are deployed at a single deployment point For a uniform distribution policy there is no knowledge about which nodes will be neighbors Increases the pdf with a group Decreases the pdf between groups Requires a larger key pool Decreases probability of sharing keys This research distributes nodes uniformly in a 2X2 grid Protocol Key Pre Distribution Global key pool S is divided into t n number of groups number of key pools Goal is to allow nearby key pools S i j to share keys with a neighboring group Si 1 j Each node contains a subset m of their groups key pool Phases 2 3 Shared key Discovery Broadcast indices of keys Setup secure links with neighbors Path Key Establishment Use previously established secure channels to setup keys with unconnected neighbors Allows intermediate nodes to determine keys Problem Intermediate nodes may be compromised choose a key known by attacker Probability of securing a link between nodes over three hops is close to one Requires communication overhead Between nodes To determine who is choosing the key Setting up Key Pools Horizontally or vertically neighboring key pools share 0 a 25 Sc keys2 Diagonal neighbors share 0 b 25 S c keys 4a 4b 1 A and B are the over lapping factors and define the amount of keys shared by neighboring groups Non neighboring groups share no keys Determining Overlapping Factors A determines shared values between horizontal vertical neighbors Connectivity 100 68 B determines shared keys with diagonal neighbors Connectivity 100 48 Key Pool Size Group S1 1 chooses Sc from S then removes those keys For each cell S1 j for j 2 n pick a Sc keys from S1 j 1 Then pick 1 a Sc from pool Repeat for each row Si j also picking b Sc keys from Si 1 j 1 Flaw There is no guarantee that a key will not percolate from one grid to the next if node j 1 can pick arbitrary keys from j Causes nodes to share keys Experimental Setup S 100 000 a 167 b 083 Number of nodes 10 000 Deployment area 1000m X 1000m t n 10 Group size number of nodes grids Grid size t X n 100m 100 nodes per group Communication Range R 40m Sc 1770 for each group Evaluation Local Connectivity Probability that two neighboring nodes share a key M number of keys Evaluation cont Global Connectivity relation between size of isolated components and size of graph Excludes nodes outside of communication range since this is due to deployment and not key distribution Communication Overhead As number of keys increase in memory communication required decreases Point of Uncertainty If each group shares only 1770 keys a lot of keys are reused unnecessarily 100 nodes per group 100 keys per node Do we need 100 keys per group Is group connectivity guaranteed to be 100 Questions