1. A secure and scalable rekeying mechanism for hierarchical wireless sensor networks Authors: Song Guo, A-Ni Shen, and Minyi Guo Source: IEICE Transactions on Information and Systems, Vol.E93D, No.3, p.p.421-429, 2010. Presenter: Yung-Chih Lu ( 呂勇志 ) Date: 2010/12/02 1

2. Outline Introduction Related Work ◦ Basic Predistribution and Local Collaboration- Based Group Rekeying Scheme (B-PCGR) Proposed Scheme Security Analysis Performance Evaluation Conclusion Comment 2

3. Introduction (1/2) Goal ◦ Rekeying ◦ Against attack  Eavesdropping attack  Node capture attack  Forward secrecy  Backward secrecy ◦ Saving resource  Computation cost  Communication cost  Storage Overhead 3

4. Introduction (2/2) Wireless Sensor Networks Cluster Head: High-End Sensor AP: Access Point Sensor Node: Low-End Sensor Pure flat WSNsThree-tier hierarchical WSNs 4

5. Basic Predistribution and Local Collaboration- Based Group Rekeying Scheme (1/3) Key pre-distribution phase ◦ Sensor Node   Ex: g(x)=3x 2 +5x 1 +2, x=0,1,2,… g(x) distribution Base Station g(x): a t-degree g-polynomial :Sensor node g(x) W. Zhang and G. Cao, IEEE INFOCOM, 2005. 5

6. Basic Predistribution and Local Collaboration- Based Group Rekeying Scheme (2/3) Setup phase SISI g(x) Step1: Generates Step2: Calculates Step3: Sends e si (x,S j ) to Sj Step4: Removes g(x) and e si (x,y) Ex: g(x) =3x 2 +5x 1 +2, t=2 Step1: e(x,y) = x 2 y 1 +4y 1 +5, t=2, u=1 Step2: e(x,1) = x 2 +9 g’(x) = 4x 2 +5x+11 Step3: e(x,2)=2x 2 +13 e(x,3)=3x 2 +17 e(x,y): a bivariate (t,u)-degree e-polynomial s i : the Id of sensor node i S 1 : 1 S 2 : 2 S 3 : 3 S3S3 S2S2 Secure Channel Step3 g’(x) Step4 6

7. Basic Predistribution and Local Collaboration- Based Group Rekeying Scheme (3/3) Rekeying Phase ◦ Sensor node  g’(x), x=0,1,2,…  e sj (x,S i ), j ≠i SISI S3S3 S2S2 Secure Channel g’(x) Step1: e(0,2)=2x 2 +13 =13 e(0,3)=3x 2 +17 =17 Step2: S 2 sends (2,13) to S 1 S 3 sends (3,17) to S 1 Step3: To reconstruct the polynomial e(0,y)=5+4y Step4: computes g(0)=g’(0)-e(0,1) =11-9 =2 e(x,2)=2x 2 +13 e(x,3)=3x 2 +17 Step2 7

8. Proposed Scheme (1/2) Key pre-distribution phase ◦ Cluster Head  Id  K BS,CHa  K CHa,Si ◦ Sensor node  Id  K BS,Si  K CHa,Si K: a pair-wise key BS: Base Station 8

9. Proposed Scheme (2/2) Group key establishment and rekeying CH a SiSi Generates a R k i E(R k i, K CHa,Si ) 1. Generates a Group key GK k a 2. E(g k a (x), GK k-1 a ) GK k a = g k a (R k i ) Ω a : a set of all compromised nodes detected in cluster-a k: k-th 9

10. Security Analysis n c : The average number of sensor nodes in a cluster ω: The number of compromised nodes in a cluster t,u: The degree of a polynomial L key : The number of bits of a key L id : The number of bits of an id Verification-Based Group Rekeying (VGR) 10

11. Performance Evaluation n c : The average number of sensor nodes in a cluster ω: The number of compromised nodes in a cluster t,u: The degree of a polynomial L key : The number of bits of a key L id : The number of bits of an id 11

12. Conclusion Robustness to the node capture attack Reactive rekeying capability to malicious nodes Low communication and storage overhead 12

13. Comment the degree of a polynomial ≧ the number of sensor nodes in a cluster Compare ECC with polynomial IDS is a heavy burden for the cluster head. IDS: Intrusion Detection System ECC: Elliptic Curve Cryptography 13