This paper considers the use of polar codes to enable secure transmission over parallel relay channels. By exploiting the properties of polar codes over parallel channels, a polar encoding algorithm is designed based on Channel State Information (CSI) between the legitimate transmitter (Alice) and the legitimate receiver (Bob). Different from existing secure transmission schemes, the proposed scheme does not require CSI between Alice and the eavesdropper (Eve). The proposed scheme is proven to be reliable and shown to be capable of transmitting information securely under Amplify-and-Forward (AF) relay protocol, thereby providing security against passive and active attackers.
This paper considers the use of polar codes to enable secure transmission over parallel relay channels. By exploiting the properties of polar codes over parallel channels, a polar encoding algorithm is designed based on Channel State Information (CSI) between the legitimate transmitter (Alice) and the legitimate receiver (Bob). Different from existing secure transmission schemes, the proposed scheme does not require CSI between Alice and the eavesdropper (Eve). The proposed scheme is proven to be reliable and shown to be capable of transmitting information securely under Amplify-and-Forward (AF) relay protocol, thereby providing security against passive and active attackers.
In this study, by exploiting the properties of finite‐length polar codes, the authors introduce a physical layer encryption scheme to make secure (from a computational security perspective) and efficient communication between a sender (Alice) and a legitimate receiver (Bob) against both active and passive attacks, simultaneously. To prevent active attacks, two techniques are considered: (i) a novel method is introduced to keep the generator matrix of polar code secret from an active attacker (Oscar); (ii) a proper joint polar encoding/encryption algorithm based on the hidden generator matrix is introduced. Two additional strategies are considered against passive attacks: (i) a new method is introduced to partition the bit‐channels into good and bad bit‐channels and then the scrambled information bits are transmitted over those bit‐channels that are good for Bob but bad for a passive attacker (Eve); (ii) the secret key cryptography is implemented at the physical layer, such that Eve cannot decode the eavesdropped data without the knowledge of the secret key shared between the authorised parties. Besides, this study discusses efficiency analysis results consisting key size, error performance and computational complexity of the proposed scheme.
Physical layer security (PLS) enables secure communication which is independent of cryptography. It generally requires the legitimate channel being advantageous, otherwise, relaying techniques can be adopted to enhance the legitimate transmission and/or suppress the wiretap one. However, untrusted relays become new threatens since unknown passive eavesdroppers may approach either the transmitter or the receiver to wiretap the secure messages. Regarding the threatens in this setup, we propose a nonlinear transmit and relaying approach to protect the secure messages during the overall transmission. The essential idea is that Alice transmits a nonlinear transform of the original secure signal and the relays collaboratively invert the nonlinear transform at Alice when forwarding it to Bob. By carefully designing the layout of the relays, only a confined region where Bob locates is accessible to the non-distortion version of the original secure signal, and there is no secure signal leakage nearby Alice or the relays. Specifically, the proposed scheme consists of two phases. In the first one, a well-chosen nonlinear transform is applied to the secure signal of Alice, and she then broadcasts the transformed signal to both the relays and the eavesdropper. Each relay determines its forwarding approach by using either the Taylor series or the Lagrange inversion theorem on the nonlinear function of Alice to facilitate the perfect recovery of the original secure signal for Bob. In the second phase, the relays process the received signals using the well-designed forwarding approach and then cooperatively send them to Bob. The forwarding signals are aggregated at Bob and the original secure signal can be recovered directly without any further complicated equalization. We therefore define the region with this property by the secure-information-accessible region, and then provide the secrecy suggestions of laying the relays to shrink it. In contrast, the eavesdropper cannot get any useful secure information from either the first phase or the second one if it locates out of this region. Finally, we analyze both the bit error rate and the secrecy rate, and compare them with the existing secrecy methods. Numerical results validate the proposed nonlinear secrecy approach.
In this article, a new relay-aided secure communication system is investigated, where a transmitter sends signals to a destination via an amplify-and-forward (AF) relay in the presence of an eavesdropper. We consider a general system configuration, where the source, relay, destination, and eavesdropper are all equipped with multiple antennas. In the practical scenarios of unknown eavesdropper's channel state information (CSI) and uncertainty of the eavesdropper's location, we aim to maximize the expected value of the system secrecy rate over the presumed distribution of the eavesdropper's channels, by exploiting the artificial noise (AN) transmitted by the source and relay nodes. The system design issue is formulated as a nonconvex stochastic optimization problem with a source transmission power constraint and a nonconvex relay transmission power constraint. A novel computational method is proposed to solve this challenging problem. The new method is developed based on an exact penalty function method together with a parallel stochastic decomposition algorithm. Numerical simulations are performed to study the effectiveness of the proposed scheme at various locations of the eavesdropper. Simulation results show that for most cases, secure communication can be achieved without the CSI knowledge of eavesdropper's channels, and the achievable secrecy rate follows the trend of a benchmark system where the eavesdropper's full CSI is available. In particular, the achievable system secrecy rate increases with the number of antennas at the legitimate users. Moreover, the optimal power allocated for the transmission of the AN increases with the system signal-to-noise ratio. The proposed computational method achieves a higher system secrecy rate than a conventional penalty function based approach.
The security of the multi-relay wiretap system with an eavesdropper is investigated in this paper, where the amplify-and-forward (AF) relaying protocol is used. Appropriate distributed precoding design at the relay nodes can be utilized to guarantee the secure communication, which means maximizing the ratio of received signal power at the destination node and the eavesdropper node. In decode-and-forward relaying systems, an iterative algorithm has been proposed to find sub-optimum distributed precoding angles at all the relay nodes [1]. In this paper, this algorithm is extended to be used in AF systems with some modifications. In the algorithm, after receiving the equivalent channel state information (CSI) from the last relay node, the current relay node derives the optimum distributed precoding angle, and updates the equivalent CSI for the next one, so that each relay node shares much less CSI information with each other, compared with the exhaustive search scheme. Numerical and simulation results demonstrate that in the AF protocol system, the iterative algorithm can help achieve considerable secrecy capacity with a little CSI sharing overhead.
We consider secret key agreement based on radio propagation characteristics in two-way relaying system where two legitimate parties named Alice and Bob communicate with each other via a relay. In this system, Alice and Bob share secret keys generated from their radio propagation characteristics by the help of the relay. In this paper, we present two secret key agreement schemes: an amplify-and-forward (AF) scheme and a multiple-access amplify-and-forward (MA-AF) scheme. In both of the schemes, the basic idea is to share the effective fading coefficient between Alice and Bob and use it as the source of secret keys. The AF scheme is based on a conventional amplify-and-forward two-way relaying method, while the MA-AF scheme utilizes the inherent combining of signals provided by simultaneous transmissions over a multiple-access channel in order to share the secret keys more securely efficiently. We analyze eavesdropping strategy in terms of eavesdropper's location and show that if the eavesdropper is located near the relay and can receive signals from the relay without multipath fading and noise, the AF scheme is not secure. Simulation results show that the MA-AF scheme is more secure and efficient than the AF scheme.
The Physical Layer Security (PLS) technology has been proved to be an effective way to reduce information leakage in wireless communication networks. This paper discusses the problem of secure transmission for Amplify-and-Forward (AF) cooperative network which contains both an external eavesdropper and some untrusted relays at the same time, where each relay acts as a helper of transmitting information and a potential eavesdropper. We adopt the technology of Cooperative Jamming (CJ), which yields a significant performance in terms of providing a better level of security against eavesdropping and improving the secure transmission performance of the system. First we discuss the security performance of this new system model, give the secrecy rate in theory and derive a tight lower bound of this secrecy rate. Then we propose a relay selection scheme, which avoids using the channel state information (CSI) of external eavesdropper, to transmit information. Afterward, we also discuss the problem of power allocation in order to maximize the secrecy rate.