Tracing Malicious Relays in Cooperative Wireless Communications

A cooperative communication system explores a new dimension of diversity in wireless communications to combat the unfriendly wireless environment. While this emerging technology is promising in improving communication quality, some security problems inherent to cooperative relay also arise. This paper investigates the security issues in cooperative communications under the context of multiple relay nodes using decode-and-forward strategy, where one of the relay nodes is adversarial and tries to corrupt the communications by sending garbled signals. We show that the conventional physical-layer signal detector will lead to a high error rate in signal detection in such a scenario, and the application-layer cryptography alone will not be able to distinguish the adversarial relay from legitimate ones. To trace and identify the adversarial relay, we propose a cross-layer tracing scheme that uses adaptive signal detection at the physical layer, coupled with pseudorandom tracing symbols at the application layer. Analytical results for tracing statistics as well as experimental simulations are presented to demonstrate the effectiveness of the proposed tracing scheme