Annual Conference of ITA ACITA 2009

1. C C C C F F F F Annual Conference of ITA ACITA 2009 H[m] Bob Alice H[m] HAE[m] HEB[m] HBE[m] HEA[m] Bootstrapping Coalition MANETs: Physical-Layer Security under Active Adversary Murtaza A. Zafer, Dakshi Agrawal and Mudhakar Srivatsa IBM T. J. Watson Research, Hawthorne, NY, USA Eve Why we may need wireless secret-key exchange.. What should a secret-key protocol provide ? the size of secret-key shared Good secret-key protocol should trade-off Bob(B) Alice (A) the message-bits needed in the protocol Eve (E) - adversary • Alice and Bob want to setup secure communication • Phy-layer problem ? – Establish an un-jammed, efficient wireless channel under an active adversary; Solution:CDMA/FDMA phy-layer • Where’s the key ? – Low probability of detection modulations require a shared secret key ! • Pre-shared secret key may NOT be always available • Coalition network with dynamically changing membership • Centralized key management expensive for large scale networks • Need for on-demand sharing of secret key in the field !! • Why minimize message-bits ? – communicating bits is expensive over open wireless channels due to adversarial jamming! A self-evident fact overlooked by the prior literature. We propose a more relevant performance metric: What is the research problem that we solved ? Our results & conclusions.. • Recently, a class of information-theoretic protocols that exploit “wireless-channel reciprocity” has become very popular (Mobicom’08 [1], CCS’07 [2], ISIT’06 [3], etc.) for secret-key establishment • Our questions • Can we exploit channel reciprocity in military scenarios? • Is there a fundamental limit on this class of secret-key establishment protocols? • [1] S. Mathur, W. Trappe, N. Mandayam, C. Ye, and A. Reznik, “Radio-telepathy: Extracting a secret key from an unauthenticated wireless channel,” in ACM Intl. Conf. on Mobile Computing and Networking (Mobicom 2008), Sept. 2008 • [2] B. Azimi-Sadjadi, A. Kiayias, A. Mercado, and B. Yener, “Robust key generation from signal envelopes in wireless networks,” in CCS ’07: Proceedings of the 14th ACM Conference on Computer and Communications Security, Nov. 2007, pp. 401–410 • [3] C. Ye, A. Reznik, and Y. Shah, “Extracting secrecy from jointly Gaussian random variables,” in 2006 IEEE International Symposium on Information Theory (ISIT’06), July 2006, pp. 2593–2597 • Graph above: X-axis is adversary’s relative signal strength, Y-axis is the performance limit of info-theory protocols • Perf. criterion – number of message-bits required per bit of secret key • Cautionary conclusion: Info-theory schemes based on channel reciprocity are ineffective against an active Eve – they require an increasing number of (and too many) message-bits per key-bit with increasing Eve’s signal power Theoretical analysis details Secret-key protocol steps Two-step Quantization Wireless signal model High-rate Quantization Lower bound on the performance metric r(p) • Slepian-Wolf limit on message-bits • Entropy limit on key size that can be shared