1. KAIS T A lightweight secure protocol for wireless sensor networks 윤주범 2007.12. 4 ELSEVIER Mar. 2006

2. Contents Introduction Security goals Assumption LCG-based security protocols Performance analysis Conclusions and future work 2 A lightweight secure protocol for wireless sensor networks

3. Introduction (1/2) Linear Congruential Generator (LCG) One of the oldest and best-known pseudorandom number generator algorithms Easy to understand, easily implemented and fast Asymmetric cryptography Not suitable in wireless sensor networks Require expensive computations and long messages Symmetric cryptography can be used in WSN RC5, MD5, SHA1, … The performance depends on the encryption primitives. 3 A lightweight secure protocol for wireless sensor networks

4. Introduction (2/2) In this paper We propose a more lightweight block cipher that is suitable for WSN Propose a lightweight block cipher based on LCG Our proposed block cipher is more lightweight than RC5 Related work All sequences generated by the LCG are predictable (by Knuth). To use LCGs is dangerous, unless the sequence can be isolated from another generator. (Ritter[9]) 4 A lightweight secure protocol for wireless sensor networks

5. Security goals Confidentiality Achieved through encryption Integrity Detect tampering Authenticity Come from the intended sender 5 A lightweight secure protocol for wireless sensor networks

6. Assumption Existence of a key management scheme Network-wide shared key among the nodes Compromise of any single node Locally shared by a node and its neighbors Only decrypt the messages from nodes in its own group Setting up pairwise keys on the fly How to set up pairwise keys on the fly is a non-trivial task Assumption There exists a key management subsystem The assumption is reasonable Based on the key pre-distribution protocol, each sensor node could share a secret key with other nodes 6 A lightweight secure protocol for wireless sensor networks

7. LCG-based security protocols (1/4) Why selecting LCG Simplest, most efficient, well-studied PRNG To protect the random sequences Enough amount of sequences is not known to the attacker Linear congruential generators Generate random numbers for keys X n+1 = a X n + b mod m, n = 0, 1, 2, …, (1) Parameters of LCG X 0, a, b, m 7 A lightweight secure protocol for wireless sensor networks

8. LCG-based security protocols (2/4) Predictability of LCGs How many numbers are needed to infer the entire sequence?  Implement Plumstead’s inference algorithm[7] against LCG Plumstead’s algorithm 8 A lightweight secure protocol for wireless sensor networks

9. LCG-based security protocols (3/4) Analysis of Plumstead’s algorithm O(log 2 m) in worst case Empirical results of Plumstead’s algorithm  Prevent the adversary from retrieving five or more 9 A lightweight secure protocol for wireless sensor networks

10. LCG-based security protocols (4/4) Key selection Goal Hide all random numbers Chosen-plaintext attack cannot be conducted a, b, m – open X 0 – only shared secret Our system relies on the LCG’s statistical randomness For efficiency 2 63 < a < 2 64 and 2 127 < m < 2 128 10 A lightweight secure protocol for wireless sensor networks

11. Basic hop by hop message transmission (1/3) Our secure data transmission scheme Secure data aggregation - example 11 A lightweight secure protocol for wireless sensor networks

12. Basic hop by hop message transmission (2/3) Message encryption Goal of encryption Prevent recovering all the random numbers 16 bytes in size P + X1 mod 256 Permutation Decryption X1 -> C1,C2 -> p1,p2 12 A lightweight secure protocol for wireless sensor networks

13. Basic hop by hop message transmission(3/3) Security analysis Confidentiality Not feasible to exhaustively search Use a half of each byte in Bi  collision  difficult to recover Bi Authenticity and Integrity Cipher Block Chaining - MAC 4-byte MAC (brute forcing take about 20 months in 19.2 kbs channel) 13 A lightweight secure protocol for wireless sensor networks

14. Performance analysis (1/2) Number of basic operations aX n + b mod m  (2 63 < a < 2 64 and 2 127 < m < 2 128 ) Result 14 A lightweight secure protocol for wireless sensor networks Ideal case Don’t consider random number generation 8-bit Atmega

15. Performance analysis (2/2) 15 A lightweight secure protocol for wireless sensor networks

16. Conclusions Lightweight block cipher Security Random noise Random permutation Secure protocol for WSNs More efficient than RC5 Future work Implement our mechanisms on MICA2 sensor nodes Integrate our protocol with other existing WSN applications 16 A lightweight secure protocol for wireless sensor networks