1. 1 Adaptive key pre-distribution model for distributed sensor networks Author: C.-S. Laih, M.-K. Sun, C.-C. Chang and Y.-S. Han Source: IET Communications, vol. 3, no. 5, pp.723-732, 2009. (Impact Factor = 0.751) Presenter: Yung-Chih Lu Date: 2010/08/20

2. 2 Outline Introduction Proposed Scheme Performance Evaluation Security Analysis Conclusion

3. 3 Introduction(1/3) Distributed Sensor Network Base station location finding system mobilizer transceiver Unit sensing unitprocessing unit sensor digital/ analog converter microprocessor storage device power unit Power generation Sensor Architecture

4. 4 Introduction(2/3) key agreement protocol  Key pre-distribution: Keys are distributed to all sensor nodes prior to deployment.

5. 5 Introduction(3/3) Constraints  Limited energy consumption  Low transmission range  Limited Memory overhead Requirements  High network connectivity  Robust resilience against node capture  Low communication overhead

6. 6 Eschenauer-Gligor Scheme(1/3) Key pre-distribution phase Key pool Keys Key identifier Key pool Keys Key identifier Key ring (k keys) H-sensor Key identifier = key mod 2 32 K ci = E Kx (ci) Kx = K 1 ⊕,…, ⊕ K k ci = H-Sensor ID H-Sensor : L-Sensors ID 、 L-Sensors key identifiers and K ci L-Sensor : k keys 、 key identifiers and K ci :L-Sensor L-Sensor : Low-end sensor H-Sensor : High-end sensor L. Eschenauer and V. Gligor. “A Key-Management Scheme for Distributed Sensor Networks.” In Proc. 9th ACM Conference on Computerand Communication Security, pp.41-47, Nov. 2002.

7. 7 Eschenauer-Gligor Scheme(2/3) Shared-key discovery Key ring (k keys) H-sensor :L-Sensor Step1: Each L-sensor Broadcasts a list of key identities. Step2: L-sensor runs a challenge- response protocol if L-sensor find the common key. E ki (α) α = D ki [E ki (α)]

8. 8 Eschenauer-Gligor Scheme(3/3) Path-key establishment Key ring (k keys) H-sensor :L-Sensor E kc (k p ) E kp (α) α = D kp [E kp (α)]

9. 9 Proposed Scheme(1/5) Shamir’s threshold scheme P T : prime number P T ≧ a 0 t : degree of polynomial a 0 : group key Example: t=3 ; a 0 =1234 ; n = 6 g(x) = 94x 2 +166x+1234 (1,1494);(2,1942);(3,2578); (4,3402);(5,4414);(6,5614) g(x) = 94x 2 +166x+1234 g(0) = 1234

10. 10 Proposed Scheme(2/5) Key pool S1S1 S1S1 S2S2 S2S2 SvSv SvSv Sub-key pool …………………. |S| :the number of keys in key pool v :the number of sub-key pools GK: group key |d| = |S| / v sk = sub-key ID = sub-key identifier sk ij = g i (ID ij ) i=1,2,…,v j=1,2,…,|d| g 1 (x) GK 1 g 2 (x) GK 2 g v (x) GK v

11. 11 Proposed Scheme(3/5) Key pre-distribution phase Key ring ( τ keys and key ID) S1S1 S1S1 S2S2 S2S2 SvSv SvSv ……………… Sub-key pool sensor

12. 12 Proposed Scheme(4/5) Shared-key discovery phase H-sensor :L-Sensor Step1: Each L-sensor Broadcasts a list of key ID. Step2: L-sensor runs a challenge- response protocol if L-sensor find the communication key. q’: the number of common keys E ski (α) α = D ski [E ski (α)]

13. 13 Proposed Scheme(5/5) Shared-key discovery phase Step1 ︰ Each L-sensor computes their respective bonus key rings Step2: Each L-sensor Broadcasts a list of group key ID. Step3: L-sensor runs a challenge-response protocol if L-sensor find the communication key. q’: the number of common keys Key ring ( τ keys and key ID) bonus key ring ( w group keys And group key ID)

14. 14 Performance Evaluation(1/4) a. number of groups v ＝ 30, size of the key pool |S| = 10000, size of key rings τ = 75 b. value of threshold t = 2, size of the key pool |S| = 1000, size of key rings τ = 40 Connectivity

15. 15 Performance Evaluation(2/4) Local connectivity Network connectivity

16. 16 Performance Evaluation(3/4) Connectivity

17. 17 Performance Evaluation(4/4) Communication overhead a. EG scheme b. Proposed scheme

18. 18 Security Analysis Resilience against node capture a. τ =40 and p =0.33 b. τ =40 and p =0.5 p: local connectivity

19. 19 Conclusion Dependent keys High connectivity It is able to adjust its system parameters