This paper considers communication between a base station (BS) to two users, each from one side of a simultaneously transmitting-reflecting reconfigurable intelligent surface (STAR-RIS) in the absence of a direct link. Rate-splitting multiple access (RSMA) strategy is employed and the STAR-RIS is subjected to phase errors. The users are equipped with a planar fluid antenna system (FAS) with position reconfigurability for spatial diversity. First, we derive the distribution of the equivalent channel gain at the FAS-equipped users, characterized by at-distribution. We then obtain analytical expressions for the outage probability (OP) and average capacity (AC), with the latter obtained via a heuristic approach. Our findings highlight the potential of FAS to mitigate phase imperfections in STAR-RIS-assisted communications, significantly enhancing system performance compared to traditional antenna systems (TAS) with only modest hardware complexity and negligible training or feedback overhead at the user side. Furthermore, we quantify the impact of practical phase errors on system efficiency, emphasizing the importance of robust and energy-efficient strategies for next-generation wireless networks.

Ambient backscatter communication (AmBC) has become an integral part of ubiquitous Internet of Things (IoT) applications due to its energy-harvesting capabilities and ultra-low- power consumption. However, the open wireless environment exposes AmBC systems to various attacks, and existing authentication methods cannot be implemented between resource-constrained backscatter devices (BDs) due to their high computational demands. To this end, this paper proposes PLCRA-BD, a novel physical layer challenge-response authentication scheme between BDs in AmBC that overcomes BDs’ limitations, supports high mobility, and performs robustly against impersonation and wireless attacks. It constructs embedded keys as physical layer fingerprints for lightweight identification and designs a joint transceiver that integrates BDs’ backscatter waveform with receiver functionality to mitigate interference from ambient RF signals by exploiting repeated patterns in orthogonal frequency division multiplexing (OFDM) symbols. Based on this, a challenge-response authentication procedure is introduced to enable low-complexity fingerprint exchange between two paired BDs leveraging channel coherence, while securing the exchange process using a random number and unpredictable channel fading. Additionally, we optimize the authentication procedure for high-mobility scenarios, completing exchanges within the channel coherence time to minimize the impact of dynamic channel fluctuations. Security analysis confirms its resistance against impersonation, eavesdropping, replay, and counterfeiting attacks. Extensive simulations validate its effectiveness in resource-constrained BDs, demonstrating high authentication accuracy across diverse channel conditions, robustness against multiple wireless attacks, and superior efficiency compared to traditional authentication schemes.

Passive eavesdropping compromises confidentiality in wireless networks, especially in resource-constrained environments where heavyweight cryptography is impractical. Physical layer security (PLS) exploits channel randomness and spatial selectivity to confine information to an intended receiver with modest overhead. However, typical PLS techniques, such as beamforming, artificial noise, and reconfigurable intelligent surfaces, often require additional active power or specialized deployment and rely on precise time synchronization and perfect CSI estimation, which limits their practicality. Meanwhile, the role of ambient backscatter devices (AmBDs) in potentially strengthening the legitimate channel while limiting eavesdroppers in generalized wireless network settings has not been fully investigated. To this end, we propose AmbShield, an AmBD-assisted PLS scheme that leverages naturally distributed AmBDs to simultaneously strengthen the legitimate channel and degrade eavesdroppers' reception without requiring extra transmit power and with minimal deployment overhead. In AmbShield, AmBDs are exploited as friendly jammers that randomly backscatter to create interference at eavesdroppers, and as passive relays that backscatter the desired signal to enhance the capacity of legitimate devices. We further develop a unified analytical framework that analyzes the exact probability density function (PDF) and cumulative distribution function (CDF) of legitimate and eavesdropper signal-to-interference-noise ratio (SINR), a closed-form secrecy outage probability (SOP), its high-SNR asymptote, and a secrecy diversity order (SDO). The analysis provides clear design guidelines on various practical system parameters to minimize SOP. Extensive experiments that include Monte Carlo simulations, theoretical derivations, and high-SNR asymptotic analysis demonstrate the security gains of AmbShield across diverse system parameters under imperfect synchronization and CSI estimation.

Ambient backscatter communication (AmBC) has become increasingly popular for facilitating ubiquitous Internet of Things (IoT) due to its ultra-low-power consumption and energy-harvesting capabilities. However, the open nature of wireless channels and the resource-limited devices in AmBC systems expose them to threats such as identity impersonation and wireless spoofing attacks. Recently, physical layer authentication (PLA) offered a lightweight solution to address the above security challenges by utilizing inherent wireless properties, like channel fading and signal patterns, as unique fingerprints to identify legitimate devices and distinguish them from attackers. Despite its promise, current research still lacks an effective PLA mechanism that can accurately authenticate backscatter devices (BDs) and defend against spoofing attacks in AmBC systems. This paper presents AmbAu, a two-stage PLA scheme designed to authenticate BDs by leveraging the signal correlation between an ambient source and the BD. In the initialization stage, the verifier extracts a complex covariance matrix from the downlink signals between the ambient source and the BD. This matrix is later used during the authentication stage to verify the BD's identity and detect spoofing attempts. Through security analysis, we demonstrate AmbAu's resilience against replay, relay, and counterfeiting attacks. Simulations under various conditions demonstrate AmbAu's accuracy, efficiency, and superior performance when compared to traditional PLA schemes.

This paper investigates the impact of deploying the fluid antenna system (FAS) on the performance of covert communications. In particular, we focus on a scenario where a transmitter seeks to covertly communicate with a receiver, while a warden attempts to detect the transmission. Both the receiver and the warden are assumed to utilize planar FAS. We derive compact analytical expressions for the covertness outage probability (COP), defined as the complement of the sum of false alarm (FA) and missed detection (MD) probabilities. By determining the optimal detection threshold that maximizes the COP, we characterize the success probability for the legitimate transmission, highlighting the trade-off between covertness and transmission success. Our numerical results confirm that while deploying FAS at the warden enhances its detection ability compared to fixed-position antennas (FPAs), equipping the receiver with FAS rather than FPAs significantly improves reception quality, leading to more reliable transmission.

This paper examines the impact of emerging fluid antenna systems (FAS) on reconfigurable intelligent surface (RIS)-aided secure communications. Specifically, we consider a classic wiretap channel, where a fixed-antenna transmitter sends confidential information to an FAS-equipped legitimate user with the help of an RIS, while an FAS-equipped eavesdropper attempts to decode the message. To evaluate the proposed wireless scenario, we first introduce the cumulative distribution function (CDF) and probability density function (PDF) of the signal-to-noise ratio (SNR) at each node, using the central limit theorem and the Gaussian copula function. We then derive a compact analytical expression for the secrecy outage probability (SOP). Our numerical results reveal how the incorporation of FAS and RIS can significantly enhance the performance of secure communications.

The rapid evolution of communication technologies and the emergence of sixth-generation (6G) networks have introduced unprecedented opportunities for ultra-reliable, low-latency, and energy-efficient communication. Integrating technologies like non-orthogonal multiple access (NOMA) and wireless powered communication networks (WPCNs) brings new challenges. These include energy constraints and increased security vulnerabilities. Traditional antenna systems and orthogonal multiple access schemes struggle to meet the increasing demands for performance and security in such environments. To address this gap, this paper investigates the impact of emerging fluid antenna systems (FAS) on the performance of physical layer security (PLS) in WPCNs. Specifically, we consider a scenario in which a transmitter, powered by a power beacon via an energy link, transmits confidential messages to legitimate FAS-aided users over information links while an external eavesdropper attempts to decode the transmitted signals. Additionally, users leverage the NOMA scheme, where the far user may also act as an internal eavesdropper. For the proposed model, we first derive the distributions of the equivalent channels at each node and subsequently obtain compact expressions for the secrecy outage probability (SOP) and average secrecy capacity (ASC), using the Gaussian quadrature methods. Our results reveal that incorporating the FAS for NOMA users, instead of the TAS, enhances the performance of the proposed secure WPCN.

This paper proposes a novel physical layer authentication (PLA) scheme for backscattering tag-to-tag networks (BTTNs), where aTalker Tag(TT) communicates passively with a Listener Tag (LT) in the presence of a potential adversary. Designed for ultra-low power tags without cryptographic capability, the proposed PLA leverages the unique voltage profiles generated by the tags’ energy harvesting and demodulation circuits to form physical-layer signatures for authentication. In addition, to enhance the reliability of voltage measurements, especially under weak signal conditions inherent within BTTNs, an indoor reconfigurable intelligent surface (RIS) is integrated to improve the received signal quality at LT. The proposed approach maintains a high authentication success rate even as the distance between TT and LT increases. A detailed security analysis demonstrates strong resilience against impersonation, man-in-the-middle, relay, and replay attacks, as long as the RIS controller remains secure. This robustness stems from the adversary’s inability to recreate the exact voltage profiles at LT, due to the inherent location-specific channel characteristics and the RIS-assisted signal shaping that the attacker cannot replicate. Furthermore, the simulation results confirm the effectiveness of the proposed RIS-assisted PLA, showing significant gains in authentication performance and secrecy capacity across diverse deployment scenarios.

Physical Unclonable Functions (PUFs) are hardware-based mechanisms that exploit inherent manufacturing variations to generate unique identifiers for devices. Dynamic Random Access Memory (DRAM) has emerged as a promising medium for implementing PUFs, providing a cost-effective solution without the need for additional circuitry. This makes DRAM PUFs ideal for use in resource-constrained environments such as Internet of Things (IoT) networks. However, current DRAM PUF implementations often either disrupt host system functions or produce unreliable responses due to environmental sensitivity. In this paper, we present EPUF, a novel approach to extracting random and unique features from DRAM cells to generate reliable PUF responses. We leverage bitmap images of binary DRAM values and their entropy features to enhance the robustness of our PUF. Through extensive real-world experiments, we demonstrate that EPUF is approximately 1.7 times faster than existing solutions, achieves 100% reliability, produces features with 47.79% uniqueness, and supports a substantial set of Challenge-Response Pairs (CRPs). These capabilities make EPUF a powerful tool for DRAM PUF-based authentication. Based on EPUF, we then propose a lightweight authentication protocol that not only offers superior security features but also surpasses state-of-the-art authentication schemes in terms of communication overhead and computational efficiency.

Fluid antenna system (FAS) is gaining attention as an innovative technology for boosting diversity and multiplexing gains. As a key innovation, it presents the possibility to overcome interference by position reconfigurability on one radio frequency (RF) chain, giving rise to the concept of fluid antenna multiple access (FAMA). While FAMA is originally designed to deal with interference mainly by position change and treat interference as noise, this is not rate optimal, especially when suffering from a strong interference channel (IC) where all positions have strong interference. To tackle this, this paper considers a two-user strong IC where FAMA is used in conjunction with simultaneous non-unique decoding (SND). Specifically, we analyze the key statistics for the signal-to-noise ratio (SNR) and interference-to-noise ratio (INR) for a canonical two-user IC setup, and subsequently derive the delay outage rate (DOR), outage probability (OP) and ergodic capacity (EC) of the FAMA-IC. Our numerical results illustrate huge benefits of FAMA with SND over traditional fixed-position antenna systems (TAS) with SND in the fading IC.

Backscatter communication (BC) represents a wireless communication technology that facilitates the transmission of data by low-power devices, referred to as backscatter devices (BDs), through the modulation or reflection of pre-existing wireless signals, typically sourced from an access point (AP). The advent of the Internet of Things (IoT) has garnered significant attention and witnessed the widespread adoption of BC, primarily due to its exceptional energy- efficiency characteristics. Nevertheless, the security of BC systems faces substantial threats when deployed in practical scenarios due to their inherent openness. Specifically, wireless BDs, which directly engage with users, are susceptible to detrimental consequences in the event of interactions with counterfeit wireless APs. Owing to their non-authenticated and unconditional reflection properties, BDs are vulnerable to spoofing attacks orchestrated by malicious APs. Moreover, their limited computing capabilities make it challenging to employ intricate cryptographic algorithms. To tackle these challenges, we introduce APAuth, a lightweight authentication scheme that leverages the power value of BD to establish AP authentication. In this scheme, BDs and APs share a confidential key and engage in negotiations to determine a key generation algorithm. Subsequently, the current stored power value of BD is utilized to calculate the power value that must be delivered to BD from AP. If the computed charging power value aligns with the value determined by the key generation algorithm, the AP successfully passes the authentication of BD. We perform a thorough theoretical analysis of the security aspects inherent in our proposed scheme. We further conduct numerical simulations to validate the practical viability and desired performance of APAuth in diverse real-world scenarios.

This paper studies the performance of a wire-less powered communication network (WPCN) under the non-orthogonal multiple access (NOMA) scheme, where users take advantage of an emerging fluid antenna system (FAS). More precisely, we consider a scenario where a transmitter is powered by a remote power beacon (PB) to send information to the planar NOMA FAS-equipped users through Rayleigh fading channels. After introducing the distribution of the equivalent channel coefficients to the users, we derive compact analytical expressions for the outage probability (OP) in order to evaluate the system performance. Additionally, we present asymptotic OP in the high signal-to-noise ratio (SNR) regime. Eventually, results reveal that deploying the FAS with only one activated port in NOMA users can significantly enhance the WPCN performance compared with using traditional antenna systems (TAS).

A smart grid (SG) is an advanced electrical grid that enhances the efficiency and reliability of traditional power grids. Reconfigurable intelligent surfaces (RISs) have been recently proposed to enhance communication performance in the SG. However, the communication links between different SG components could suffer from eavesdropping and unauthorized access, which makes physical layer security (PLS) a promising solution for addressing these concerns. In this article, we focus on exploring the effect of applying RIS on enhancing the PLS performance of SG communications. Specifically, we consider an RIS with reflecting elements besides a smart meter, a neighborhood gateway (NG), and an eavesdropper to develop a smart environment in the SG to improve PLS performance in terms of secrecy outage probability (SOP) and average secrecy capacity (ASC). For this purpose, we first derive a probability density function and a cumulative distribution function for the signal-to-noise ratio (SNR) at both the NG and the eavesdropper. Then, we derive closed-form expressions of SOP and ASC to evaluate the impact of various system parameters on the secrecy performance of RIS-aided SG communications. Furthermore, considering the significance of system behavior under high-SNR conditions, we conduct an asymptotic analysis of the SOP and ASC. Finally, we apply the Monte Carlo simulation to validate the analytical results. Our results indicate that using the RIS can significantly enhance the secrecy performance of SG communications compared to the conventional SG scenarios without the RIS.

With the maturity of the Internet of Things (IoT), many IoT applications have been popularized and promoted. As one of the IoT technology, backscatter communication (BC) has aroused research interest due to its low-cost and ultra-low power consumption characteristics. Due to their simple design and battery-less functionalities, backscatter devices (BDs) have been introduced as the main candidates for deploying in smart home networks (SHN). Although batch authentication in BC systems is crucial and efficient for SHN security, existing schemes have only focused on radio frequency identification (RFID) devices and no literature has given a general solution for BD batch authentication. In this paper, we propose a scheme named BatAu for authenticating batch BDs applied in SHN by extracting physical layer features in multiplexing signals. We conduct numerical simulations with various settings to show its desirable performance.

Abstract In 2018, Abbasinezhad‐Mood and Nikooghadam (IEEE Transaction on Smart Grid, pp 6194–6205, 9(6), 2018) proposed an ultra‐lightweight secure scheme for neighbourhood area network () communications in smart grid. They have claimed that their protocol is secure against all known attacks in environment by providing informal security analysis besides a formal analysis which was done by using an automatic verification tool. However, by performing several attacks, this study shows that their scheme has serious security flaws. After performing each attack, lightweight countermeasures is proposed for securing their protocol against that attack.

Recently, bionic signals have been used to achieve covert underwater acoustic communication (UWAC) with high signal-to-noise ratios (SNRs) over transmission systems. A high SNR allows the attackers to proceed with their mischievous goals and makes transmission systems vulnerable against malicious attacks. In this paper we propose an improved Merkle hash tree based secure scheme that can resist current underwater attacks, i.e., replay attack, fabricated message attack, message-altering attack, and analyst attack. Security analysis is performed to prove that the proposed scheme can resist these types of attacks. Performance evaluations show that the proposed scheme can meet UWAC limitations due to its efficiency regarding energy consumption, communication overhead, and computation cost.