Legitimate Receiver Research Articles

A novel scatterer model for the security of key generation based on DISC model

Physical layer security is a method of extracting encryption keys according to the randomness of reciprocal propagation channels between legitimate users, and the security under normal circumstances is ensured according to the decorrelation between these channels and those tapped by eavesdropper. However, evidences show that in some scenarios, such as the environment of quasi-static or insufficient scattering, the tapped channel still has a strong correlation with the legitimate channel, leading to bits leakage and security imperilment of key generation. The effect of introducing scatterers has been experimentally proved, however, these studies are based on fixed positions or special models and there is yet a lack of research on the influences brought by various scatterer distributions. In this paper, we introduce scatterers into single-bounced DISC model and control their distributions through a probability density function with two degrees of freedom, aiming to deeply investigate the impacts of scatterer distribution on channel decorrelation as well as key security. Simulation results prove that spiral correlation between tapped channel and legitimate channel can be effectively reduced by increasing scatterers and arranging them around the legitimate receiver, which make contributions to reduce key leakage and improve security.

Energy Minimization for Robust Secure Transmission in UAV Networks With Multiple Colluding Eavesdroppers

This letter investigates an unmanned aerial vehicle (UAV) aided wireless network where a UAV transmits confidential data to multiple legitimate receivers (LRs) in the presence of multiple colluding eavesdroppers (Eves) with imperfect location information. We formulate a mixed-integer non-convex optimization problem to minimize the UAV energy consumption by jointly designing the robust trajectory and user scheduling, while ensuring that the required amount of data can be safely transmitted to LRs. Instead of resorting to $\mathcal S$ -Procedure commonly used in existing studies, we equivalently convert the problem to a more tractable form with the difficulty arising from the uncertainties in Eves’ locations effectively resolved. After that, a penalty-based iterative algorithm is proposed to obtain a suboptimal solution with the aid of the block coordinate descent and successive convex approximation techniques. The remarkable energy-saving effect of the proposed scheme is demonstrated by numerical results.

Improving the covertness in the physical-layer authentication

A well-designed Physical-Layer Authentication (PLA) scheme should consider three properties: covertness, robustness, and security. However, the three properties always cause some dilemmas, e.g., higher covertness leading to lower robustness. This paper concerns the problem of improving the covert- ness without sacrificing the robustness. This problem is important because of the following reasons: reducing the errors in recovered source message, improving the security, and ease of constructing a multi-factor authentication system. In this paper, we propose three covert PLA schemes to address the problem. In the first scheme, we improve the covertness by reducing the modification ratio on the source message based on an encoding mechanism. In the second scheme, we improve the covertness by optimizing the superimposing angle, which maximizes the minimum distance between the tagged symbols and the boundary line of the demodulation decision for the source message. In the third scheme, referred to as the hybrid scheme, we further improve the covertness by jointly using the advantages of both the above two schemes. Our experimental results show that when the SNR at a legitimate receiver is 25 dB, as compared with the prior scheme, the first scheme improves the covertness by 17.74%, the second scheme improves the covertness by 28.79%, and the third scheme improves the covertness by 32.09%, while they have similar robustness as that of the prior scheme.

Reconfigurable Intelligent Surface: Reflection Design Against Passive Eavesdropping

The reconfigurable intelligent surface (RIS) is envisioned to create ultra-secure wireless networks. Previous works on the RIS-assisted security provisioning techniques assumed wiretap channel information at the transmitter, which is practically unavailable in a passive eavesdropping scenario. In this article, we consider a point-to-point anti-eavesdropping system in which a RIS is used to enable the secure transmission from a multi-antenna transmitter to a multi-antenna legitimate receiver. A passive eavesdropper, whose channel state information is completely unknown, attempts to decode the secret messages. We propose a security approach by using the reflection at the RIS as multiplicative randomness against the wiretapper. Specifically, the reflection coefficients in terms of amplitude and phase are updated in each transmission and kept private at the RIS. Through the reflection designs, the effective channel matrix is diagonalized at the legitimate receiver. In contrast, the eavesdropper receives coupled signals with the weights of the randomness at RIS. The main contributions of this article are three reflection designs and correspondingly three secure transmission schemes, which fulfills diverse requirements of the balance amongst performance metrics including the degrees of randomness, spectral efficiency, and reliability. The main benefits of the proposed secure transmission schemes are four-fold. First, the transmitter does not need to know the eavesdropper's channel states. Second, closed-form solutions for the reflection coefficients are provided. Third, the legitimate receiver has a linear decoding complexity. Fourth, the unauthorized wiretapper is unable to cancel out the multiplicative randomness and thus cannot extract much useful information. Numerical results show that exploiting the RIS as a source of multiplicative randomness provides a new perspective to improve the security of the wireless networks.

Secrecy analysis of short-packet transmissions in ultra-reliable and low-latency communications

In this paper, we investigate the secrecy performance of short-packet transmissions in ultra-reliable and low-latency communications (URLLC). We consider the scenario where a multi-antenna source communicates with a single-antenna legitimate receiver requiring ultra-high reliability and low latency, in the presence of a single-antenna eavesdropper. In order to safeguard URLLC, the source transmits the artificial noise (AN) signal together with the confidential signal to confuse the eavesdropper. We adopt a lower bound on the maximal secrecy rate as the secrecy performance metric for short-packet transmissions in URLLC, which takes the target decoding error probabilities at the legitimate receiver and the eavesdropper into account. Using this metric, we first derive a compact expression of the generalized secrecy outage probability (SOP). Then, we formally prove that the generalized SOP is a convex function with respect to the power allocation factor between the confidential signal and the AN signal. We further determine the optimal power allocation factor that minimizes the generalized SOP. The results presented in this work can be useful for designing new secure transmission schemes for URLLC.

SDR Proof-of-Concept of Full-Duplex Jamming for Enhanced Physical Layer Security.

In order to secure wireless communications, we consider the usage of physical-layer security (PLS) mechanisms (i.e., coding for secrecy mechanisms) combined with self-interference generation. We present a prototype implementation of a scrambled coding for secrecy mechanisms with interference generation by the legitimate receiver and the cancellation of the effect of self-interference (SI). Regarding the SI cancellation, four state-of-the-art algorithms were considered: Least mean square (LMS), normalized least mean square (NLMS), recursive least squares (RLS) and QR decomposition recursive least squares (QRDRLS). The prototype implementation is performed in real-world software-defined radio (SDR) devices using GNU-Radio, showing that the LMS outperforms all other algorithms considered (NLMS, RLS and QRDRLS), being the best choice to use in this situation (SI cancellation). It was also shown that it is possible to secure communication using only noise generation by the legitimate receiver, though a variation of the packet loss rate (PLR) and the bit error rate (BER) gaps is observed when moving from the fairest to an advantageous or a disadvantageous scenario. Finally, when noise generation was combined with the adapted scrambled coding for secrecy with a hidden key scheme, a noteworthy security improvement was observed resulting in an increased BER for Eve with minor interference to Bob.

Secrecy Zone Achieved by Directional Modulation With Random Frequency Diverse Array

This work analyzes the impact of the transceivers' relative locations on the physical layer security achieved by directional modulation with a random frequency diverse array (DM-RFDA). Based on the adopted path loss model, we first derive the probability of non-zero secrecy capacity, denoted by pn, achieved at a legitimate receiver for an eavesdropper with a fixed location. We then examine how far we need to push the eavesdropper away from the transmitter in order to guarantee pn ≥ δ, where δ is a given value determining a certain level of security. The results reveal that the DM-RFDA system ensures a high level of security (e.g., δ = 0.95) for the legitimate user who is significantly further away from the transmitter than the eavesdropper. Furthermore, the results demonstrate that it is easier to guarantee the required level of security when there are more resource (e.g., higher bandwidth and a larger number of transmit antennas) in the DM-RFDA system.

Secrecy Enhancing of SSK Systems for IoT Applications in Smart Cities

The secure exchange of messages between different communication devices is a major issue of Internet-of-Things (IoT) applications in future smart cities. Current security mechanisms focus on multiple antennas technology, such as spatial modulation (SM), but in space shift keying (SSK), there is still a space to explore. In this article, we propose a secrecy-enhancing SSK scheme for IoT applications by applying security technologies in the physical layer wherein the number of transmit antennas is arbitrary rather than the value of power of two. In this scheme, the security performance of the communication system is improved by using two technologies, namely, artificial noise (AN) and antenna selection. We assume that the application scenario of the SSK system is under the classic eavesdropping model. First, we design ANs according to the channel state information (CSI) to interrupt the eavesdropper and benefit the legitimate receiver via the appropriate cancellation technology. Second, the antenna selection method is designed based on the signal to leakage noise ratio (SLNR) to further boost the secrecy performance by expanding the mutual information difference between the main channel and the eavesdropping channel. Results from our simulations indicate that by the use of the proposed scheme, significant secrecy enhancing can be achieved in terms of bit error ratio (BER) and secrecy rate (SR) when compared with existing schemes. This achieved secrecy enhancing can benefit the suitable IoT communication applications in the smart city environment to avoid the leakage of data transmission.

Defending wireless communication against eavesdropping attacks using secret spreading codes and artificial interference

The broadcast nature of wireless communication makes it intrinsically vulnerable to eavesdropping attacks. This article suggests the using of secret spreading codes (i.e. only a legitimate receiver knows the spreading sequence) and artificial interference (i.e. by intentionally adding noise to the broadcast channel) on countering eavesdropping attacks. We have made a theoretical analysis on the potential performance degradation at the eavesdropper and at the legitimate receiver for a point-to-point wireless communication system using direct-sequence spread spectrum (DSSS) with coherent phase-shift keying (PSK) modulation. We have also proposed a lightweight non-cryptographic secret code generation scheme which leads to low correlation between the spreading codes used at the transmitter and at the eavesdropper. Simulation results confirms the good anti-eavesdropping performance on using the proposed non-cryptographic secret code generation scheme. Simulation results also conform with the theoretical analysis and motivate the using of artificial interference on countering eavesdropping attacks.

Secure Millimeter-Wave Ad Hoc Communications Using Physical Layer Security

Millimeter-wave (mmWave) communications are highly promising to improve the capacity of modern wireless networks, while the physical layer security (PLS) techniques hold great potential to enhance the critical secrecy performance therein. By carefully exploiting the significant signal difference between the Non-Light-of-Sight (NLoS) and Line-of-Sight (LoS) mmWave links, this paper proposes a Sight-based Cooperative Jamming (SCJ) scheme to improve the PLS performance of mmWave ad hoc communications. In this scheme, each potential jammer that has no LoS link to its nearest receiver but may have LoS links to eavesdroppers is selected with a certain probability to generate artificial noise such that channel advantages at legitimate receivers can be achieved. For performance modeling of the new jamming scheme, novel and efficient theoretical approximation approaches are firstly developed to enable the challenging issue of interference distribution modeling to be tackled, and then a theoretical framework based on stochastic geometry is proposed to capture the secrecy transmission capacity behavior under the SCJ scheme. Finally, extensive numerical results are provided to illustrate the SCJ scheme under various network scenarios.

Hardware Impaired Ambient Backscatter NOMA Systems: Reliability and Security

Non-orthogonal multiple access (NOMA) and ambient backscatter communication have been envisioned as two promising technologies for the Internet-of-things due to their high spectral efficiency and energy efficiency. Motivated by this fact, we consider an ambient backscatter NOMA system in the presence of a malicious eavesdropper. Under the realistic assumptions of residual hardware impairments (RHIs), channel estimation errors (CEEs) and imperfect successive interference cancellation (ipSIC), we investigate the physical layer security (PLS) of the ambient backscatter NOMA systems with emphasis on reliability and security. In order to further improve the security of the considered system, an artificial noise scheme is proposed where the radio frequency (RF) source acts as a jammer that transmits interference signals to the legitimate receivers and eavesdropper. On this basis, the analytical expressions for the outage probability (OP) and the intercept probability (IP) are derived. To gain more insights, the asymptotic analysis and corresponding diversity orders for the OP in the high signal-to-noise ratio (SNR) regime are carried out, and the asymptotic behaviors of the IP in the high main-to-eavesdropper ratio (MER) region are explored as well. Finally, the correctness of the theoretical analysis is verified by the Monte Carlo simulation results. These results show that compared with the non-ideal conditions, the reliability of the considered system is high under ideal conditions, but the security is low.

Improved physical layer security of visible light communications with focused light emitters

A conventional secure visible light communication (VLC) system that is composed of one transmitter, one friendly jammer with multiple light-emitting-diodes, one legitimate receiver and one eavesdropper is considered. We propose the use of an optical lens at the legitimate transmitter as an additional effective and practical security measure. We investigate the secrecy rate of a Gaussian wiretap channel VLC scenario inside a room. First, we consider friendly jamming through optimal power allocation between the information and the jamming signal. Then, we investigate the improved security through the use of the optical lens into the system. The use of this collimating thin lens spatially limits the transmitted information to a confined and adjustable area that is beneath the transmitter. Through simulation results we demonstrate that the use of the optical lens can significantly improves the secrecy rate by focusing the information transmission. We also design and implement an experimental test-bed and demonstrate the applicability of the proposed approach. We experimentally validate that the system is practically realizable, and the numerical simulations are consistent with our measurement results. Although the proposed scenario necessitates the receiving unit to be located in a stationary position, we showcase that the hardware implementation is simple, practical, and significantly lower in cost as opposed to a beam-forming type VLC system that offers directional beam forming to send the information towards a dynamic receiver. Furthermore, through a careful adjustment of the distance between the transmitter and the lens, it is possible to control the size of the region where a receiver can access the data. Both experimental and simulation results show that, with the utilization of a lens at the transmitter, VLC is a promising candidate for applications where the secrecy is a critical concern.

Antenna Grouping-Based Blind Artificial Noise for TDD Secure Transmission

The artificial noise (AN-) aided techniques have been considered as promising candidates to enhance the physical layer security. However, the effect of AN on an eavesdropper (Eve) can be severely degraded as the number of antennas at Eve increases. To resolve this problem, we propose an antenna grouping-based blind artificial noise (AG-BAN) to prevent Eve from being aware of the existence of AN in multiple-input, single-output, and multi-antenna eavesdropper (MISOME) and multiple-input, multiple-output, and multi-antenna eavesdropper (MIMOME) channels. In the proposed AG-BAN, antennas at a legitimate transmitter (Alice) are classified into two antenna groups, which are used to transmit the data and AN, respectively. In the antenna group for transmitting the AN, the null-space-based AN scheme is employed, which makes the AN be nullified at a legitimate receiver (Bob). Any reference signals are not transmitted from the antenna group assigned to transmit the AN. As a result, Eve cannot perceive the AN, which makes the AG-BAN be effective even if there is a sufficient number of antennas at Eve. In the proposed AG-BAN, the estimated secrecy capacity at Alice is used for the antenna grouping criterion, which is derived based on the Eve’s channel statistics without the instantaneous channel information between Alice and Eve. Furthermore, to reduce the computational complexity of the exhausted search based optimal antenna grouping, the proposed AG-BAN employs one-by-one antenna search procedures. The simulation and numerical results show that the proposed AG-BAN scheme effectively improves the secrecy capacity compared to the conventional AN schemes and achieves the near-identical secrecy capacity compared to the exhausted search based optimal AG-BAN scheme.

Improved LPD Characteristics for QS-DS-CDMA Employing Randomization Techniques

Easily and flexibly deployable ad-hoc communication networks emerging in tactical military or even civilian contexts, frequently suffer from poor synchronization due to lack of coordinating infrastructure. In addition to synchronization issues, and especially in military settings, security from the aspect of detectability is also of crucial importance. Imperfect synchronization can be dealt with by making use of Quasi-Synchronous Code Division Multiple Access (QS-CDMA), relying on Loosely Synchronous Codes to maintain orthogonality in the presence of limited time delays. Security, in terms of low probability of detection (LPD) from the standpoint of a malicious adversary, can be improved (reduced detection) by employing randomization techniques that disrupt the inherent structure of the transmitted QS-CDMA signals. This is based on the fact that QS-CDMA signals are Cyclostationary, having (almost) periodic Auto-Correlation functions (ACF) due to eminent signal periodicities (such as spreading code repetition). In this paper, we propose techniques to disturb the ACF and equivalently the Spectral Correlation function, and reduce the Degree of Cyclostationarity (DCS), our LPD measure. Specifically, we investigate randomization via 1) random per symbol time dithering and 2) random selection of spreading sequences, as well as a hybrid approach combining time dithering and code randomization. In all proposed techniques knowledge of the randomization pattern is not required at the legitimate receiver. We derive the Spectral Correlation function of the QS-CDMA signal under the proposed randomization schemes and compare it to simulations. We show through analysis and extensive numerical simulations that the proposed technique can reduce the DCS by almost two orders of magnitude. We also show that enhanced LPD can be achieved using the proposed techniques while sacrificing a part of the reduced time synchronization requirement. We further analyze the implications of the friendly receiver not knowing the randomization pattern and present results on the resulting communication performance.

Covert MIMO Communications Under Variational Distance Constraint

The problem of covert communication over Multiple-Input Multiple-Output (MIMO) Additive White Gaussian Noise (AWGN) channels is investigated, in which a transmitter attempts to reliably communicate with a legitimate receiver while avoiding detection by a passive adversary. The covert capacity of the MIMO AWGN is characterized under a variational distance covertness constraint when the MIMO channel matrices are static and known. The characterization of the covert capacity is also extended to a class of channels in which the legitimate channel matrix is known but the adversary's channel matrix is only known up to a rank and a spectral norm constraint.

Security Model of Authentication at the Physical Layer and Performance Analysis over Fading Channels

Compared with conventional authentication schemes, which utilize cryptographic mechanisms and operate at an upper layer, authentication at the physical (PHY) layer possesses many advantages, such as, higher information-theoretic security by introducing uncertainty to an adversary, better efficiency, and better compatibility by avoiding any operations at the upper layer. An effective PHY-layer authentication scheme should consider covertness, security, and robustness together. However, in published literature, these three properties have been separately analyzed. This paper proposes a generic security model for PHY-layer authentication, and we design a new systematic metric, which is referred to as the probability of security authentication (PSA). According to the proposed generic security model, we can not only systematically analyze the effect of the parameter of a certain PHY-layer authentication scheme on the final performance, but also fairly compare the performance of different PHY-layer authentication schemes under the same channel conditions at the legitimate and adversary receivers. For performance analysis, the probability of detection (PD) and the probability of false alarm (PFA) of two PHY-layer authentication schemes over fading channels are defined, and their closed-form expressions are well derived. On the basis of the proposed generic security model, a systematic performance comparison between different PHY-layer schemes is provided.

Secrecy Energy‐Efficient UAV Communication via Trajectory Design and Power Control

This paper investigates the problem of maximizing the secrecy energy efficiency (SEE) for unmanned aerial vehicle‐ (UAV‐) to‐ground wireless communication system, in which a fixed‐wing UAV tries to transmit covert information to a terrestrial legitimate destination receiver with multiple terrestrial eavesdroppers. In particular, we intend to maximize the worst‐case SEE of UAV by jointly optimizing UAV’s flight trajectory and transmit power over a finite flight period. However, the formulated problem is challenging to solve because of its large‐scale nonconvexity. For efficiently solving this problem, we first decouple the above optimization problem into two subproblems and then propose an alternating iterative algorithm by adopting block coordinate descent method and Dinkelbach’s algorithm as well as successive convex approximation technique to seek a suboptimal solution. For the sake of performance comparison, two benchmark schemes, the secrecy rate maximization (SRM) scheme and constrained energy minimization (CEM) scheme are considered to obtain more useful insights. Finally, simulation results are executed to verify that our proposed SEE maximization (SEEM) algorithm is superior to two benchmark schemes for the UAV‐ground communication system.

Optimal Secure GDoF of Symmetric Gaussian Wiretap Channel With a Helper

We study a symmetric Gaussian wiretap channel with a helper, where a confidential message is sent from a transmitter to a legitimate receiver, in the presence of a helper and an eavesdropper, under a weak notion of secrecy constraint. For this setting, we characterize the optimal secure generalized degrees-of-freedom (GDoF). The result reveals that, adding a helper can significantly increase the secure GDoF of the wiretap channel. The result is supported by a new converse and a new scheme. In the proposed scheme, the helper sends a cooperative jamming signal at a specific power level and direction. In this way, it minimizes the penalty in GDoF incurred by the secrecy constraint. In the secure rate analysis, the techniques of noise removal and signal separation are used.

Toward Physical-Layer Security for Internet of Vehicles: Interference-Aware Modeling

The physical-layer security (PLS) of wireless networks has witnessed significant attention in next-generation communication systems due to its potential toward enabling protection at the signal level in dense network environments. The growing trends toward smart mobility via sensor-enabled vehicles are transforming today's traffic environment into Internet of Vehicles (IoVs). Enabling PLS for IoVs would be a significant development considering the dense vehicular network environment in the near future. In this context, this article presents a PLS framework for a vehicular network consisting a legitimate receiver and an eavesdropper, both under the effect of interfering vehicles. The double-Rayleigh fading channel is used to capture the effect of mobility within the communication channel. The performance is analyzed in terms of the average secrecy capacity (ASC) and secrecy outage probability (SOP). We present the standard expressions for the ASC and SOP in alternative forms, to facilitate analysis in terms of the respective moment generating function (MGF) and characteristic function of the joint fading and interferer statistics. Closed-form expressions for the MGFs and characteristic functions were obtained and Monte Carlo simulations were provided to validate the results. Approximate expressions for the ASC and SOP were also provided, for easier analysis and insight into the effect of the network parameters. The results attest that the performance of the considered system was affected by the number of interfering vehicles as well as their distances. It was also demonstrated that the system performance closely correlates with the uncertainty in the eavesdropper's vehicle location.

Physical-Layer Security of SIMO Communication Systems over Multipath Fading Conditions

The present work investigates the physical layer security of wireless communication systems over non-homogeneous fading environments, i.e., η-μ and λ-μ fading models, which are typically encountered in realistic wireless transmission scenarios in the context of conventional and emerging communication systems. This study considers a single-input multiple-output system that consists of a single-antenna transmitter, a multi-antenna legitimate receiver, and an active multi-antenna eavesdropper. To this end, novel exact analytical expressions are derived for the corresponding average secrecy capacity and secrecy outage probability, which are corroborated by respective results from computer simulations. Capitalizing on the offered results, the physical layer security is quantified in terms of different parameters, which leads to useful insights on the impact of non-homogeneous fading environment and the number of employed antennas on the achieved physical layer security levels of the underlying system configuration. The offered results and insights are useful for the design of such systems as well as for the computational requirements and sustainability relating to such systems, since emerging communications are largely characterized by stringent quality of service and complexity requirements.