1. Computationally Secure Hierarchical Self- Healing Group Key Distribution for Heterogeneous Wireless Sensor Networks Y.J. Yang, J.Y. Zhou, R.H. Deng, F. Bao Institute for Infocomm Research, Singapore

2. Introduction Heterogeneous WSN Architecture Basic Hierarchical Self-healing group Key Distribution Scheme Extended Scheme Conclusion Agenda

3. Introduction Heterogeneous WSN Architecture Basic Hierarchical Self-healing group Key Distribution Scheme Extended Scheme Conclusion

4. Wireless Sensor Networks Wireless Sensor Networks (WSNs)

5. Self-healing Group Key Distribution Key Distirubtion & Management is Fundamental to Other Security Issues –Pairwise key distribution –Group key distribution Self-healing group key distribution especially suits WSNs’ lossy channel.

6. All Existing Work Consider Homogeneous WSNs Homogeneous WSN –All sensor nodes have the same capability –Homogeneous WSNs have scalability problem. Theoretical and empirical studies have corroborated this Homogeneous WSNs

7. Hierarchical Self-healing Key Distribution Motivated to Study Self-healing Group Key Distribution for Heterogeneous WSNs Hierarchical Self-healing Group Key Distribution –Adapting to the heterogeneous WSN architecture

8. Introduction Heterogeneous WSN Architecture Basic Hierarchical Self-healing group Key Distribution Scheme Extended Scheme Conclusion

9. Heterogeneous WSNs Heterogeneous WSNs Are A Better Alternative to Homogeneous ones –The network is partitioned into groups, and each group is placed a group manager –Group managers have better capability than sensor nodes –A group manager acts an intermediary between sensor nodes and the base station

10. Heterogeneous WSNs

11. Introduction Heterogeneous WSN Architecture Basic Hierarchical Self-healing group Key Distribution Scheme Extended Scheme Conclusion

12. Key Hierarchy

13. Key Generation rK = [rk 1, rk 2 ] mK i = [mk 1, mk 2 ] =[h(G i,rk 1 ), h(G i,rk 2 )] gK i = …

14. Key Generation gK i [j] = k R [m-j+1]+k F [j] k R [j] = h R j (mk 1 ) = h R (h R (h R (…h R (mk 1 )))) k F [j] = h F j (mk 2 ) = h F (h F (h F (…h F (mk 2 )))) reverse hash chain foward hash chain

15. Key Distribution mk 2 is given to each sensor as seed s F for the forward hash chain At the start of each session, the group manager generates k R [m-j+1] using mk 1 as seed for the reverse hash chain, and broadcasts to sensors within its group –The broadcast scheme is essentially the Dutta et al.’s scheme, with a slight modification to rectify its weakness gK i [j] = k R [m-j+1]+k F [j]

16. Key Distribution The reverse hash chain is used to achieve self-healing property The forward hash chain is used to achive forward secrecy, i.e., sensors joined later cannot compute group keys of earlier sessions

17. Introduction Heterogeneous WSN Architecture Basic Hierarchical Self-healing group Key Distribution Scheme Extended Scheme Conclusion

18. Untrusted Group Manager For the basic scheme, group managers are assumed trusted. However, group managers cannot be guaranteed trusted. We consider some group managers are compromised in the extended scheme Untrusted Group Manager

19. Secret sharing of mk 1 In basic scheme, if mk 1 is compromised, all sessions are compromised We are left to secret sharing of mk 1 among group managers; and compute k R [m-j+1] in a distributed way The point is that h R () can be computed in a distributed way Secret sharing of mk 1

20. Choice of h R () Normal hash function cannot be used as h R () We define h R () h R (): Z N  QR N h R (x) = x 2 (mod N) mk 1 is partitioned into t shares mk 1 = s 1.s 2 …s t-1.s t (mod N) h R j (mk 1 ) = (s 1 ) 2^j (s 2 ) 2^j (s t ) 2^j (mod N)

21. Introduction Heterogeneous WSN Architecture Basic Hierarchical Self-healing group Key Distribution Scheme Extended Scheme Conclusion

22. Heterogeneous WSNs have better scalability and performance, as the introduction of powerful group managers provides shortcut for data transmission from sensors to base station We proposed hierarchical self-healing group key distribution tailored to heterogeneous WSNs Our constructions are based Dutta et al.’s idea Conclusion

23. Thank You! Q&A