In this paper, we investigate a four single-antenna node network, constituted of a transmitter, a receiver, a cooperative node and a wiretapper. The wiretapper has the ability to eavesdrop the communication or disrupt the transmission by jamming. This results in both cases in the decrease of the secrecy rate. The cooperative node on the other hand aims to improve secrecy by either relaying or jamming. We investigate the secrecy performance of the decode-and-forward and cooperative jamming strategies against this kind of adversary. To model the interaction between the helper and the wiretapper, we define an extensive form game, for which we derive the pure and mixed strategies equilibria. Finally, we compare the performance of the schemes and we analyze the equilibrium outcomes through simulation results.
In this paper, we investigate a four single-antenna node network, constituted of a transmitter, a receiver, a cooperative node and a wiretapper. The wiretapper has the ability to eavesdrop the communication or disrupt the transmission by jamming. This results in both cases in the decrease of the secrecy rate. The cooperative node on the other hand aims to improve secrecy by either relaying or jamming. We investigate the secrecy performance of the decode-and-forward and cooperative jamming strategies against this kind of adversary. To model the interaction between the helper and the wiretapper, we define an extensive form game, for which we derive the pure and mixed strategies equilibria. Finally, we compare the performance of the schemes and we analyze the equilibrium outcomes through simulation results.
The growth of wireless networks has been considerable over the last decades. Due to the broadcast nature of these networks, security issues have taken a critical role in today’s communications. A promising direction towards achieving secure communications is information theoretic secrecy, which is an approach exploiting the randomness of the channels to ensure secrecy. Based on this approach, there has been a recent surge of interest in a potential cooperation between users to enhance the secrecy of communications. In this thesis we investigate the interaction between cooperation and secrecy. In particular the contributions of the thesis can be divided into two parts. In the first part, we study cooperative strategies for secrecy for wireless channels. Our goal is to evaluate the effect of fading and limited CSI on the eavesdropper’s channels. In that purpose we consider a scenario where a helper aims at increasing the secrecy of the communication between a source and destination in the presence of an eavesdropper. Several strategies are discussed for the helper, namely decode-and-forward, amplify-and-forward, and cooperative jamming. We introduce the secrecy outage probability, the conditional secrecy outage probability and the secure throughput as secrecy measures. For each measure, we investigate and compare the secrecy performance of cooperation. We furthermore elaborate a system optimization in terms of strategy selection, node positioning, power allocation and rate design. In the second part, we consider cooperation in the 4-node scenario against a more sophisticated adversary: an active eavesdropper, which can either passively eavesdrop, or jam the transmission. A game-theoretic perspective is a natural way to analyze the competitive interaction between the helper and the eavesdropper. Therefore we define several secrecy games, for which we find the Nash and Stackelberg equilibria as well as the corresponding secrecy rate outcomes. Another important consideration in this scenario is the interaction between the source and the helper, which we model and solve as a Stackelberg game, and we illustrate its impact on the achievable secrecy rates.
This paper investigates reliable and covert transmission strategies in a multiple-input multiple-output (MIMO) wiretap channel with a transmitter, receiver and an adversarial wiretapper, each equipped with multiple antennas. In a departure from existing work, the wiretapper possesses a novel capability to act either as a passive eavesdropper or as an active jammer, under a half-duplex constraint. The transmitter therefore faces a choice between allocating all of its power for data, or broadcasting artificial interference along with the information signal in an attempt to jam the eavesdropper (assuming its instantaneous channel state is unknown). To examine the resulting trade-offs for the legitimate transmitter and the adversary, we model their interactions as a two-person zero-sum game with the ergodic MIMO secrecy rate as the payoff function. We first examine conditions for the existence of pure-strategy Nash equilibria (NE) and the structure of mixed-strategy NE for the strategic form of the game. We then derive equilibrium strategies for the extensive form of the game where players move sequentially under scenarios of perfect and imperfect information. Finally, numerical simulations are presented to examine the equilibrium outcomes of the various scenarios considered.
This paper investigates transmission strategies in a MIMO wiretap channel with a transmitter, receiver and wiretapper, each equipped with multiple antennas. In a departure from existing work, the wiretapper is able to act either as a passive eavesdropper or as an active jammer per channel use, under a half-duplex constraint. The transmitter therefore faces a choice between dynamically allocating all of its power for data; or broadcasting artificial noise along with the information signal in order to selectively degrade the eavesdropper's channel. We model the network as a zero-sum game in strategic form with the MIMO secrecy rate as the payoff function. We first carry out a detailed analysis of the various rate outcomes that result from the possible actions of the agents. We then discuss the conditions for equilibrium outcomes in the strategic form of the game. Finally, numerical simulations are presented to corroborate the analytical results.
This paper investigates transmission strategies in a MIMO wiretap channel with a transmitter, receiver and wiretapper, each equipped with multiple antennas. The secrecy rate between the transmitter and the legitimate receiver is chosen as the performance metric. In a departure from existing work, the wiretapper is able to act either as a passive eavesdropper or as an active jammer, under a half-duplex constraint. The transmitter therefore faces a choice between allocating all of its power for data; or broadcasting artificial noise along with the information signal in order to selectively degrade the eavesdropper's channel. We model the network as a dynamic zero-sum game in extensive form with the secrecy rate as the payoff function. We first examine subgame-perfect equilibrium strategies in the extensive form of the game with perfect information. We then discuss sequential and trembling hand perfect equilibria for the case of imperfect information. Finally, numerical simulations are presented to corroborate the analytical results.
In this paper, we study how to defend against full-duplex active eavesdropping attacks in the cooperative communication system. Unlike passive eavesdropping attackers, a full-duplex active eavesdropper acts as both a jammer and a classical eavesdropper in full-duplex mode, and seeks to maximize eavesdropping. Furthermore, in a real-world network, the relays may be selfish and have their own objectives due to competing/limited resources. This may lead to the failure of cooperative communication if there is no incentive to stimulate relays to participate in forwarding the transmitter's messages. Therefore, in this paper, we propose a three-stage Stackelberg game approach to model the behaviors of attacker, and the competitions among the transmitter, relays and attacker. Through finding the Stackelberg equilibrium of our scheme, the legitimate users can achieve cooperative communication to improve the secrecy capacity and to defend against full-duplex active eavesdropping attacks. Findings from the evaluations demonstrate that with an increasing number of channels, our scheme can significantly reduce the intercept probability; therefore, the security performance is improved. It is shown that our scheme can greatly improve the utilities of both the transmitter and multiple relays over the results of the Nash equilibrium scheme and rand power control scheme, which means that the relays are more willing to participate in the cooperative communication, and the transmitter can achieve better secure transmission in our scheme. We also demonstrate that our scheme outperforms other existing schemes, i.e., power control with smart jamming game in a single-channel model/multiple-channel model.
Security issue is of paramount importance yet significant challenge for wireless communications, and this problem can be even more intricate when facing with a full-duplex adversary. In this paper, we investigate the physical layer security of a legitimate transmission link in the presence of a full-duplex active eavesdropper, who is capable to perform eavesdropping and jamming simultaneously. The legitimate user aims at a target secrecy rate while the eavesdropper intends to maximize its wiretap rate. To this end, the eavesdropper imposes a jamming signal at the legitimate receiver to stimulate higher-power legitimate transmissions and thus facilitates its eavesdropping. This, however, generates residual self-interference at the eavesdropper itself and is subject to a linear price for the jamming power. The problem is then formulated within a game-theoretic framework, where the closed-form strategies of both the legitimate user and active eavesdropper are obtained. Moreover, we analyze the performance in terms of secrecy outage probability for the legitimate link in such a hostile situation. Also provided are the simulation results which validate our theoretical analysis.