1. Using Auxiliary Sensors for Pair-Wise Key Establishment in WSN Source: Lecture Notes in Computer Science (2010) Authors: Qi Dong and Donggang Liu Presenter: Hsing-Lei Wang Date: 2010/09/03

2. Outline Introduction Pair-Wise Key Establishment Analysis and Discussion Comparison Security Reinforcing Version Conclusions 2

3. Introduction The proposed scheme ’ s main idea: Deploy assisting sensor nodes to help key establishment between two regular sensor nodes Advantages: Very high probability of establishing a shared key Majority of sensors only need to store a single key High resilience to node compromise Implementation on TelosB Motes 3

4. Protocol Description(1/3) Initialization Let = network size, = assisting sensor nodes Base station generates Master Key for node Assisting node will get preloaded with For instance, 1MB flash memory can store the hash images for 128,000 nodes (1 hash image=8bytes) 4

5. Protocol Description(2/3) Pair-Wise Key Establishment Assisting node i = 1,2,…,m 5

6. Protocol Description(3/3) Supplemental Key Establishment 6

7. Analysis and Discussion (1/3) Probability of Establishing Keys: 7

8. Analysis and Discussion (2/3) Resilience against Node Capture 8

9. Analysis and Discussion (3/3) Overheads Storage: regular sensor: a single master key assisting sensor: n hash values Computation: a few symmetric key operations and hash operations Communication: only one-hop range communication are needed in most case 9

10. Comparison (1/2) Security Performance Setting: Network size n =20,000 nodes Neighbors d =50 nodes Each sensor store =200 keys P=Probability of direct key between two sensor 10

11. Comparison (2/2) Security Performance Setting: Network size n =20,000 nodes Neighbors d =50 nodes Each sensor store =200 keys P=Probability of direct key between two sensor 11

12. Security Reinforcing Version Security issue: Once an assisting node is compromised, the attacker will get all the hash values and discover all the random keys generated by the node Method to fix: Set a sequence number =0 and in initialization After setup a pair-wise key between u and v, 12

13. Conclusion This paper developed a novel scheme to establish the pair-wise keys in WSN Using of assisting sensor The analysis indicates the scheme has several significant advantages over existing scheme High probability to establishing shared keys Good resilience against node capture Lower overhead (storage, computation, etc.) 13