Security Issues in Cooperative Communications: Tracing Adversarial Relays

Cooperative communication system explores a new dimension of diversity in wireless communications to combat unfriendly wireless environment through strategic relays. While this emerging technology is promising in improving communication quality, some security problems inherent to cooperative relay also arise. In this paper we investigate the security issues in cooperative communications that consist of multiple relay nodes using decode-and-forward strategy. In particular, we consider the situation 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 detection will not be effective in such a scenario, and the application-layer cryptography alone is not sufficient to identify the adversarial relay. To combat adversarial relay, we propose a cross-layer scheme that uses pseudo-random tracing symbols, with an adaptive signal detection rule at the physical layer, and direct sequence spread spectrum symbol construction at the application layer for tracing and identifying adversarial relay. Our experimental simulations show that the proposed tracing scheme is effective and efficient