A lightweight secure protocol for wireless sensor networks

1. 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 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. 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]) A lightweight secure protocol for wireless sensor networks

5. Security goals • Confidentiality • Achieved through encryption • Integrity • Detect tampering • Authenticity • Come from the intended sender 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 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 • Xn+1 = a Xn + b mod m, n = 0, 1, 2, …, (1) • Parameters of LCG • X0, a, b, m 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 A lightweight secure protocol for wireless sensor networks

9. LCG-based security protocols (3/4) • Analysis of Plumstead’s algorithm • O(log2 m) in worst case • Empirical results of Plumstead’s algorithm  Prevent the adversary from retrieving five or more 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 • X0 – only shared secret • Our system relies on the LCG’s statistical randomness • For efficiency • 263 < a < 264 and 2127 < m < 2128 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 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 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) A lightweight secure protocol for wireless sensor networks

14. Performance analysis (1/2) • Number of basic operations • aXn + b mod m  (263 < a < 264 and 2127 < m < 2128) • Result Don’t consider random number generation Ideal case 8-bit Atmega A lightweight secure protocol for wireless sensor networks

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