Two-Hop Secure Communication Using an Untrusted Relay
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Research Article Two-Hop Secure Communication Using an Untrusted Relay Xiang He and Aylin Yener Wireless Communications and Networking Laboratory, Electrical Engineering Department, The Pennsylvania State University, University Park, PA 16802, USA Correspondence should be addressed to Aylin Yener, [email protected] Received 4 December 2008; Revised 8 August 2009; Accepted 8 October 2009 Recommended by Hesham El-Gamal We consider a source-destination pair that can only communicate through an untrusted intermediate relay node. The intermediate node is willing to employ a designated relaying scheme to facilitate reliable communication between the source and the destination. Yet, the information it relays needs to be kept secret from it. In this two-hop communication scenario, where the use of the untrusted relay node is essential, we find that a positive secrecy rate is achievable. The center piece of the achievability scheme is the help provided by either the destination node with transmission capability, or an external “good samaritan” node. In either case, the helper performs cooperative jamming that confuses the eavesdropping relay and disables it from being able to decipher what it is relaying. We next derive an upper bound on the secrecy rate for this system. We observe that the gap between the upper bound and the achievable rate vanishes as the power of the relay node goes to infinity. Overall, the paper presents a case for intentional interference, that is, cooperative jamming, as an enabler for secure communication. Copyright © 2009 X. He and A. Yener. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction Information theoretic security was proposed by Shannon [1]. The idea of measuring secrecy using mutual information lends itself naturally to the investigation of how the channel can influence secrecy and further to the characterization of the fundamental limit of secure transmission rate. Wyner, in [2], defined the wiretap channel, and showed that secure communication from a transmitter to a “legitimate” receiver is possible when the signal received by the wiretapper (eavesdropper) is degraded with respect to that received by the legitimate receiver. Reference [3] identified the secrecy capacity of the general discrete memoryless wiretap channel. The secrecy capacity of the Gaussian wiretap channel is found in [4]. Recent progress in this area has extended classical information theory channel models to include secrecy constraints. Examples are the multiple access channel, the broadcast channel, the two-way channel, the three-node relay channel and the two-user interference channel [5–13]. These studies are beginning to lead to insights for designing secure wireless communication systems from the physical layer up. Prominent such examples include using multiple antennas
to steer the transmitted signal away from an eavesdropper [14–1
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