Secure Walking GPS: A Secure Localization and Key Distribution Scheme for Wireless Sensor Networks

1. Secure Walking GPS:A Secure Localization and Key Distribution Schemefor Wireless Sensor Networks Qi Mi 1, John A. Stankovic 1, Radu Stoleru 2 1 University of Virginia, 2 Texas A&M University

2. Outline • Introduction • Secure Walking GPS • Evaluation • Conclusion

3. Node Localization • Why is localization important for WSN applications? • We care about where an event takes place. • Many other WSN services depend on localization. • Challenges • Accuracy • Cost • Practicality • Security

4. Our Contributions • An integral solution to localization and key distribution • Secure against the Dolev-Yao, wormhole, and GPS-denial attacks. • The number of keys distributed to each node is small. • A security analysis demonstrating the correctness • Performance evaluation using parameters from a real WSN deployment • High localization accuracy • High neighbor connectivity • Nice scaling property • Accommodates irregular radio pattern as well • Low overhead

5. Attack Model • Attacker’s Goal • Steal sensitive data from legitimate messages • Inject false messages into the network • Disrupt the normal WSN services and applications • Attack Types • Dolev-Yao attack (overhear, intercept, synthesize) • Wormhole attack (low-latency communication) • GPS-denial attack

6. Assumptions • Assumptions • A secure base • A powerful and trustworthy master node with GPS and IG modules • Trustworthy GPS signals • Communication between the master node and each sensor node is not jammed • Manual deployment of sensor nodes

7. Pre-Deployment • Purposes • Download program code to each sensor node si • Distribute to each sensor node a unique deployment key for individual secure communication with the master node M • Note:Each deployment key is known only by the master node and one sensor node. Takes place in the secure base. Communication is unencrypted.

8. Deployment When a new sensor node is manually deployed, the master node determines its currentlocation and m communication keys, and sends them to the node securely using its deployment key.

9. Location Acquisition • The master node provides exclusive location information. • GPS Module • Acquire location from GPS signals • More accurate, but not always available • Inertial Guidance Module • Motion sensors + Accelerometers • Estimate the current location using Dead Reckoning • Less accurate, but always available • Must be recalibrated with the GPS module whenever possible to avoid error accumulation Location information provided by the GPS module is always preferred.

10. Location-Based Key Distribution • Distance-Bounding Rule • Two sensor nodes are allowed to share a communication key only if they are physical neighbors, thus protecting the WSN against the wormhole attack. • Connectivity Rule • Each sensor node needs to share a communication key with at least one of its already deployed physical neighbors so as to ensure neighbor connectivity. Each sensor node obtains m communication keys from the master node. Theorem: Assume same circular range. Let N be the max neighbor count.

11. An Example of Location-Based Key Distribution For simplicity, assume a circular uniform communication range and each sensor node obtains 5 communication keys. Notations:si: The ith deployed sensor nodeKiC: The communication key set distributed to si.kj: The jth communication key drawn from key pool P. Note:kjin grey is set to non-distributable, while kjin bold is a currently distributable key chosen to make up KiC.

12. Post-Deployment • Neighbor Discovery • Broadcast encrypted messages • ACK • Random Key Selection • Confuse attacker’s judgment • Defeat attacker’s attempt to figure out a correct key

13. Security Analysis • Resistance to Dolev-Yao Attack • All communication during the deployment is well encrypted. • Resistance to Wormhole Attack • No nodes which are beyond each other’s communication range can share a key, assuming perfect localization. • Even if there may exist potential wormhole links due to imperfect localization, the impact is small and local. • Resistance to GPS-Denial Attack • The Inertial Guidance module acts as an alternative to the GPS module.

14. Evaluation • Metrics • Average Localization Error • Average Neighbor Connectivity • # of legitimate links vs # of potential wormhole links • Simulation Setup • Probability of GPS availability p: [.75, 1.00] • Size of communication key set: 5 • Regular communication range: 30 meters in all directions • Irregular communication range: ~ U(15, 45) meters in each 1˚ direction • GPS localization error: ~ U(-1.5, 1.5) meters • IG degree estimation error: ~ U(-10, 10) degrees • IG distance estimation error: ~ U(0, 3) meters

15. Evaluation (cont’d) • Line Deployment (regular radio) • 500 nodes with the same regular radio pattern: r = 30 meters • Horizontal spacing: ~ N(10, 2) meters • Vertical offset: ~ N(0, 2) meters • 30 runs of simulations • Grid Deployments (regular radio) • 500 and 1000 nodes with the same regular radio pattern: r = 30 meters • Grid size: 10 meters • Horizontal spacing: ~ N(10, 2) meters • Vertical offset: ~ N(0, 2) meters • 30 runs of simulations

16. Evaluation (cont’d) • Grid Deployment (irregular radio) • Average localization error: [0.73, 1.31] meters • Average neighbor connectivity: [0.52, 0.85] • # of legitimate links: [1627, 1740] • # of potential wormhole links: [17, 222]

17. Evaluation (cont’d) • Overhead • Hardware overhead • The GPS and Inertial Guidance modules can be reused for multiple deployments. • Communication overhead • Increased # of messages in the network, due to the fact that not all pairs of neighbors necessarily share a communication key. • Storage overhead • We need (1+5)x8=48 bytes for keys, when m is 5 and AES 128-bit is used. • MICAz has an EEPROM of 8K bytes

18. Conclusion • Secure Walking GPS is practical, low-cost, and scales well. • It provides accurate localization results. • By carefully distributing the communication keys, it makes the deployed WSN resistant to the Dolev-Yao, wormhole, and GPS-denial attacks. • The current design only permits uni-cast or multicast. It is worth exploring an improved scheme that enables broadcast.

19. Q & A Thank you!