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Adaptive Random Key Distribution Schemes for Wireless Sensor Networks

Adaptive Random Key Distribution Schemes for Wireless Sensor Networks. Shih-I Huang Dept. of Comp. Sci. & Info. Eng. National Chiao Tung University WADIS’03. Outline. Introduction Motivation Related Work Proposed Schemes Analysis Conclusion. Introduction.

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Adaptive Random Key Distribution Schemes for Wireless Sensor Networks

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  1. Adaptive Random Key Distribution Schemes for Wireless Sensor Networks Shih-I Huang Dept. of Comp. Sci. & Info. Eng. National Chiao Tung University WADIS’03

  2. Outline • Introduction • Motivation • Related Work • Proposed Schemes • Analysis • Conclusion

  3. Introduction • Wireless Sensor Networks (WSNs) • It consists of a set of small devices with sensing and wireless communication capabilities • Those small devices are named sensor nodes, and are deployed within a special area to monitor a physical phenomenon. • Ex: Anthrax • Multifunctional • Depends on what sensors are attached • Features • Widely deployed. (100~1M↑) • Low communication bandwidth • Limited memory space and computation power

  4. Motivation • A large WSN consists of thousands of nodes • Need shared communication keys to ensure secure peer-to-peer wireless communication • Limited memory storage (512 bytes ~ 4K) • To deliver data without being compromised, WSN services rely on secure communication and key distribution

  5. Conventional Scheme (Random Pair-wise) K2 K3K4K5K6K7 K5 K1 K2K3K4K6K7 K1 K1 K2K3K5K6K7 K1 K3K4K5K6K7 K2 K4 K1 K2K3K4K5K6 K7 K3 K6 K1 K2K4K5K6K7 K1 K2K3K4K5K7 * Requires a large storage space for keys in a large WSN

  6. Motivation • The existing key distribution solutions require a large memory space in a large WSN • We propose two symmetric key distribution schemes to minimize storage requirement • Adaptive Random Pre-distributed scheme (ARP) • Unique Assigned One-way Hash Function scheme (UAO)

  7. Related Work

  8. Random Graph Theory • A Random Graph G(n, p) is a graph of n nodes, and the probability that a link exists between any two nodes is p. • Given a desired probability Pc for the graph connectivity • ex: Pc=0.99999 to get a connected graph. • Then we can get a threshold of p to form a connected graph. • ……. (1) • The expected degree of a node • ….…(2) * The scheme only needs to select d keys to keep a network connected under probability p

  9. Communication keys Sensor nodes Random Key Based Schemes • Basic Scheme • L. Eschenauer, V. D. Gligor, “A Key-Management Scheme for Distributed Sensor Networks,” 9th ACM Conference on Computer and Communication Security, pp.41-47, November 2002. (CCS’02) • Each node randomly picks r keys from a unordered key pool S. • Use the common shared key to establish a secure link. • Relies on probabilistic key sharing among the nodes of a random graph. B B B A A A C C C D D D Secure link * Map Random Graph Theory to key selecting problem

  10. Adaptive Random Pre-distributed Scheme (ARP Scheme) • The features of ARP scheme • A Random Key based key distribution scheme for WSNs. • To minimize the memory requirement. • ARP scheme consists of • Two-Dimension Key Pool • Key Selecting Algorithm

  11. Two-Dimension Key Pool • Use t one-way function F1, F2,…,Ft and t seed keys K1,0, K2,0,…,Kt,0 to generate t one-way key chains. • For a key chain KCi, it consists of Ki,0, Ki,1,…Ki,s-1. • Where Ki,j = Fi(Ki,j-1), and the length of KCi is s. • The key pool size = s * t.

  12. Key Selecting • Each node randomly choose a one-way key chain, and memorized its one-way function Fi and its seed key Ki,0. • Randomly select d-t key chains KCt1, KCt2,…,KCt(d-t), from the rest of key chains. • For each key chain KCtjselected, randomly pick a key Ktj,sj from KCtj and memorized Ktj,sj.

  13. Unique Assigned One-way Hash Function Scheme (UAO Scheme) • The features of UAO scheme • Provide node-to-node authentication. • Great resistance to node capture. • The maximum supported network size is greater than the existing schemes. • The UAO scheme consists of • Key Decision Algorithm • Node-to-Node Authentication Protocol

  14. K2 = F2(IDi) SN5 SN4 SN3 SN7 SN1 SNi SN6 SN2 K5 = F5(IDi) K2 ID2 K5 ID5 K7 ID7 K7 = F7(IDi) Key Decision Algorithm • Suppose each sensor node SNi has a unique identity IDi. • First, we assign a unique one-way hash function Fi to each sensor node SNi. • Second, SNi randomly selects d other sensor nodes. • Third, each selected node use following formula to generate the unique key for SNi. • Finally, SNi memorizes those unique keys and the generating identities. IDi Fi

  15. SNj SNi Node-to-node Authentication Protocol 1 • SNi broadcasts its identity • SNj verifies its key ring, if IDi is combined with any key then • SNi calculates the Ks = Fi(IDj), and decrypts the message, then sends the ACK and challenge message. • SNjreceives the challenge and sends the response 2 3 4

  16. Analysis of ARP Scheme • We analyze the ARP scheme in following aspect: • Probability of connectivity. • Analyze the link probability of using Two-Dimension Key Pool. • The link probability is equal to 1 – Pr[any two nodes do not share any key]

  17. Probability of Connectivity (1/2) • To calculate the probability that any two nodes A and B do not share any common key: • A’s one-way key chain does not match with B’s one-way key chain. • A’s one-way key chain does not match with any B’s selected keys. • The probability of above two parts is equal to • A’s selected keys do not match with B’s one-way key chain. • The probability is equal to • A’s selected keys do not match with any B’s selected keys. • The probability is equal to • The link probability is equal to • ……(3)

  18. Probability of Connectivity (2/2) Key pool size = 100,000 * ARP needs fewer keys to achieve the same connectivity probability

  19. Analysis of UAO Scheme • The link probability p’ can be evaluate by 1 – Pr.[two nodes do not have any key derived from the other’s one-way function] • p’ is equal to • Substitute p’ by a function of d: • Substitute d by a function of n: • Evaluate the root of the above equation: r: Key ring size

  20. Evaluation of UAO Scheme Key size = 128 bits Pc=0.99999

  21. Conclusion • Key distribution is a critical and fundamental issue for the security service in WSNs. • The pre-distributed and symmetric cryptosystem based scheme is well suitable for the resource constrained sensor networks. • We propose two schemes based on one-way function and Random Graph theory to provide memory efficient key distribution for WSNs. • ARP scheme • Provide efficient trade-off between memory space and security strength. • UAO scheme • Provide node-to-node authentication. • Great resistant to node capture. • If there is enough memory space, we suggest using UAO scheme as the key distribution scheme for WSNs. • Otherwise, we suggest using ARP scheme. • To achieve an efficient trade-off between memory space and security strength.

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