This work investigates the vulnerability of analog network coding (ANC) to physical layer attacks from adversarial users, when all nodes are equipped with multiple antennas. Specifically, we examine the MIMO two way relay channel (TWRC) with two users trying to communicate with each other via a relay node in the presence of a passive eavesdropper. We propose a new performance metric, namely the secrecy sum rate of the MIMO TWRC, to quantify performance. We then consider secure transmission strategies for the scenarios of no eavesdropper channel state information at the transmitters (ECSIT) and complete ECSIT, respectively. Finally, numerical results are presented to illustrate the improvement in secrecy obtained with the proposed transmission schemes.
This work investigates the vulnerability of analog network coding (ANC) to physical layer attacks from adversarial users, when all nodes are equipped with multiple antennas. Specifically, we examine the MIMO two way relay channel (TWRC) with two users trying to communicate with each other via a relay node in the presence of a passive eavesdropper. We propose a new performance metric, namely the secrecy sum rate of the MIMO TWRC, to quantify performance. We then consider secure transmission strategies for the scenarios of no eavesdropper channel state information at the transmitters (ECSIT) and complete ECSIT, respectively. Finally, numerical results are presented to illustrate the improvement in secrecy obtained with the proposed transmission schemes.
In this paper, we address the physical-layer security of two-way (bi-directional) transmissions of two terminals with the help of multiple relay nodes in the presence of an eavesdropper, where each node in the network is only equipped with single antenna. The secrecy sum rate is used as the metric of security, which is the rate difference between the legitimate information exchange between the terminals and the information leakage to the eavesdropper. We propose two-phase analog network coding (ANC) and power allocation scheme for the relay nodes and terminals to enhance the security of the data exchange. Three different schemes are proposed. The first scheme is the optimal ANC to achieve the maximum secrecy sum rate, i.e. secrecy capacity, which is found to be mathematically difficult to solve. Two suboptimal schemes are proposed with and without the instantaneous channel state information (CSI) of the eavesdropper, respectively. The solutions of both schemes are shown to be unique and globally optimum, which are solved by convex optimization techniques. Numerical evaluation results of the obtained secrecy sum rate and transmit power are provided and analyzed to show the properties and efficiency of the proposed ANCs.
In this paper, we consider the two-way relay network (TWRN) in the presence of an eavesdropper, and construct a noisy amplify-and-forward (AF) algorithm to enhance the physical (PHY) layer security capacity. All the source nodes, the relay and the eavesdropper are equipped with multiple antennas. In the proposed noisy AF scheme, the relay first receives signals from both source nodes, adds weighted artificial noise (AN), and then amplifies and forwards the modified signal to both source nodes. In this scenario, we analyze the effects of AN and the number of relay antennas on the secrecy sum rate for different conditioning channel matrices. It is shown that AN will result in an increased secrecy sum rate, and the channel condition is a key parameter of the system in deciding the sum secrecy rate. Finally, simulation results demonstrate the validity of proposed studies.
Achieving secure transmission in wireless network is a significantly important research topic. Classic cryptography encrypts a confidential message to an unreadable cipher message. Thus only the authentic receiver with correct secrecy key is able to decrypt the message. However, with the growing computational capability of adversaries, the requirement of secrecy key generation and distribution is getting stringent. Another method to achieve wireless security, which has attracted much attention in recent years, is through physical layer processing, named physical layer security. In a typical wiretap channel model consisting of a transmitter, a legal receiver and an adversary (illegal receiver), early works have proven that it is possible to achieve positive secrecy rate using multiple antenna techniques, such as beamforming, at the transmitter. In this thesis, we focus on two types of malicious behaviors of the adversary: passive eavesdropping and active attack. For the passive eavesdropping, we first consider the multi-input-single-output (MISO) wiretap channel, in which the legitimate transmitter utilizes the artificial noise aided precoding strategy to maximize the achievable secrecy rate of the channel. Both scenarios of known and unknown channel state information (CSI) for the eavesdropper channels are considered. By deriving the closed-form expression of ergodic secrecy rate, we prove that there exists an optimal power ratio between the information signal and the artificial noise. We then extend our study to a four-node fading channel model in a wireless relay network, which includes two single-antenna users, one single-antenna eavesdropper and one relay node equipped with multiple antennas. By studying the decode-and-forward (DF) scheme, cooperative jamming (CJ) scheme and one proposed hybrid relay scheme, relay-and-jamming (RJ), we aims to find the optimal relay scheme with the condition that the transmitter and the relay node are under individual power constraints and the CSI of the illegitimate channel is only statistically known. Our analysis shows that the hybrid RJ scheme is optimal when the transmitter has a relatively small power budget and/or the transmitter is far away from the intended receiver. Besides the passive eavesdropping, the adversary could also choose the active attack. The pilot spoofing attack is one active attack conducted by the adversary during the channel estimation phase of the legitimate transmission. In practical systems, the pilot signals are usually known \textit{a priori} and repeatedly used information. In this attack, an intelligent adversary spoofs the transmitter on the estimation of CSI by sending the identical pilot signal as the legitimate receiver. By doing so, the adversary could obtain a larger channel rate in the data transmission phase, and also drastically weaken the strength of the received signal at the legitimate receiver if the adversary utilizes large enough power. Due to the serious consequences caused by such an attack, we first propose an energy ratio detector (ERD) that explores the asymmetry of received signal power levels at the transmitter and the legitimate receiver when the attack occurs. Our analysis shows that the ERD could provide very high probability of detection with certain requirement on the false alarming probability. Furthermore, we design a two-way training based scheme to provide not only attack detection but also secure transmission. The two-way training based detector (TWTD) exploits the intrusive component created by the adversary, followed by a secure beamforming-assisted data transmission. In addition to the good detection performance, our scheme could estimate both legitimate and illegitimate channels, with which the beamforming could be designed for data transmission.
In this paper, we propose a novel secure transmission scheme for multiple-input multiple- output (MIMO) Two-Way relay channels, where multi- pair communication partners exchange information securely with the help of relay. By utilizing the properties of transmission medium in physical layer, our scheme can achieve high transmission efficiency as well as information theoretic security. With the secrecy capacity analysis, we show that our scheme is a secure approach under two different adversarial models: 1) untrusted relay attack model; 2) trusted relay with eavesdropper attack model. Finally, we conduct three simulations of our proposed scheme. The simulation results agree with the theoretical analysis illustrating that our proposed scheme can achieve a better performance than the existing schemes.
In this paper, a secure communication system model for massive multiple-input multiple-output (MIMO) relay networks is investigated. Specifically, physical layer secure transmission is provisioned in multi-user relay networks by employing massive MIMO, linear precoder/detectors and artificial noise generation in the presence of a passive multi-antenna eavesdropper. In particular, the achievable asymptotic secrecy rate for infinitely many relay antennas is derived. The use of random artificial noise shaping matrices is advocated for massive MIMO relays for the sake of reducing the system implementation complexity. The effects of the numbers of antennas at the relay and the eavesdropper in achieving secure communication are investigated by comparing the corresponding achievable secrecy rates.
In this letter, we propose a secure beamforming scheme for physical layer network coding (PNC)-based multiple-input multiple-output (MIMO) two-way relaying system. The relay node performs PNC mapping. An eavesdropper is attempting to intercept the user information. The channel state information (CSI) of the user-to-eavesdropper channel is imperfect at the user nodes. A robust optimization problem is formulated to design beamforming vectors at the user nodes and relay. The problem is non-convex, and an algorithm is proposed to solve that. In the numerical analysis, we discuss the convergence of the proposed algorithm and the impact of the CSI error on the performance.