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.

Backscatter Communication (BC) is an innovative wireless communication technology that is characterized by energy harvesting capability, low cost, ultra-low power consumption, and ease of maintenance. Secure communications among a group of Backscatter Devices (BDs) are crucially important to facilitate its wide applications. However, current Group Key Generation (GKG) technologies in BC systems suffer from such problems as inadequate key consistency, low key generation efficiency, suboptimal key randomness, high key generation complexity, as well as lack of group key management to ensure backward and forward secrecy. In response, this paper proposes PosGKG, a position-based group key generation and management scheme with high key consistency, efficiency, and randomness, tailored for easy deployment in a BC system with low computation and communication complexity. PosGKG leverages position information to construct shared information between devices for GKG, thereby addressing over-reliance on channel reciprocity and enhancing group key consistency. In particular, PosGKG incorporates a dynamic update mechanism for private weight vectors of BDs that are used to obtain global positions for GKG, which guarantees that the generated group key retains a high degree of randomness, even in a static environment. PosGKG not only diminishes communication and computational complexities due to the adoption of randomly changed global positions as shared information for GKG but also exhibits enhanced security under various attacks, both passive and active ones. In addition, group key management is applied to guarantee the forward and backward secrecy of PosGKG, irrespective of the changes of the BC system. Theoretical analysis and comprehensive experiments with diverse configurations validate the performance of PosGKG in terms of communication and computational complexity, key generation efficiency, key consistency, robustness, security, and environmental feasibility, with demonstrated advantages over existing technologies.

Backscatter communication (BC) is a promising wireless communication technology due to its low cost, ultra-low power consumption, and ease of maintenance. However, the broadcasting and openness nature of BC by backscattering incident radio signals for message transformation introduces severe security threats, creating a bottleneck that hinders its further development. Mutual and handover authentication across multiple access points (APs) is essential to secure large-scale BC systems containing mobile backscatter devices (BDs). However, an effective scheme is still absent in the current literature. In this paper, we propose HABC, a mutual and handover authentication scheme designed to secure BC systems, which can resist various attacks. HABC leverages the physical layer feature channel impulse response (CIR) to authenticate BD. Using secret keys, the BD can verify the source of a received signal. When a BD transits from the coverage of a source AP to a target AP, HABC supports handover authentication through the control of a server based on BD location prediction to maintain continuous communications. Theoretical analysis and numerical experimental evaluation validate the satisfactory performance of HABC in terms of accuracy and robustness, as well as its superiority through comparison with cutting-edge related work.

Backscatter communication (BC) enables resource-constrained backscatter devices (BDs) to communicate by reflecting signals from external radio frequency sources (RFSs), thereby avoiding active RF components, making it a cutting-edge technology for the ubiquitous Internet of Things (IoT). However, the open nature of BC makes it vulnerable to passive and active attacks, and existing methods fail to offer robust mutual authentication suitable for mobile BC systems while keeping a low computational overhead. To address this issue, we propose AuthScatter, an accurate, robust, and scalable physical-layer mutual authentication scheme between the RFS and multiple BDs by leveraging channel fading and random numbers as a one-time pad to protect the identity key exchange procedure during the authentication. Specifically, AuthScatter constructs shared identity keys as physical-layer fingerprints for efficient identification and employs a challenge-response authentication mechanism to enable secure key exchange between the RFS and the BD. In the authentication, the one-time pad effectively prevents eavesdropping, spoofing, replay, and counterfeiting attacks, while legitimate devices leverage channel reciprocity and random number knowledge to authenticate efficiently without channel estimation or complex processing. It is tailored for high-mobility scenarios by completing the exchange within the channel coherence time while incorporating a key-update mechanism to ensure sustained security in the long term. Additionally, it includes a re-authentication mechanism to enhance resistance against wireless attacks and a batch authentication framework leveraging time-division duplexing (TDD) to enable scalability in large-scale BC deployments. Comprehensive security analysis demonstrates the resistance of AuthScatter to various threats, including eavesdropping, identity spoofing, replay, and counterfeiting attacks. Extensive simulations further validate its high authentication accuracy across diverse channel conditions, robustness against various attack vectors, and scalability with a large number of BDs, highlighting its superiority over state-of-the-art schemes.

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.

Backscatter communication (BC) is an emerging radio technology for achieving sustainable wireless communications. However, the literature still lacks an effective secret group key generation scheme for safeguarding communications among multiple resource-constrained backscatter devices (BDs). In this paper, we propose a novel physical layer group key generation framework, BGKey, for securing backscatter communications among multiple BDs. BGKey contains three schemes: Centralized Group Key Generation (CGKG), Decentralized Group Key Generation (DGKG), and Decentralized Hierarchical Group Key Generation (DHGKG). Each scheme has its own advantages, applicable in different scenarios. We analyze the performance of BGKey schemes regarding computation and communication complexity and security under eavesdropping and three active attacks. We conduct extensive simulations with different system parameters to evaluate their performance. CGKG is the most efficient and accurate for generating a group key, but it depends on a trusted radio frequency source (RFS) and is the least secure under eavesdropping and three active attacks among three schemes. DGKG exhibits better security and higher key generation rate (KGR) against eavesdropping and three active attacks compared with CGKG. However, the bit disagreement ratio (BDR) of group key increases when the size of BD group increases. DHGKG dramatically enhances the performance of group key generation compared with DGKG and retains its excellent security against eavesdropping and three active attacks.

Backscatter communication (BC) offers a promising power-efficient communication paradigm for wireless devices with constrained energy resources. However, the innate openness and broadcast characteristics of BC raise considerable security concerns. To address this, physical layer authentication has emerged as a primary solution to enable secure BC. To facilitate efficient authentication on multiple backscatter devices (BDs), batch authentication becomes essential. Nevertheless, existing schemes have not yet bridged the research gap regarding effective batch authentication on mobile BDs with high scalability support. This paper proposes BatchAuth, a physical layer batch authentication scheme designed to authenticate multiple BDs simultaneously by leveraging orthogonal frequency-division multiple access (OFDMA) technology. BatchAuth utilizes two factors, received signal strength (RSS) and multiple channel impulse responses (CIRs), to authenticate a group of BDs and leverages a channel correlation coefficient to offset performance loss and support BD dynamicity. What’s more, a backscatter waveform design facilitates an access point (AP) in estimating the CIRs from backscattered signals. Additionally, BatchAuth possesses the capability to detect and trace potential attackers by analyzing the specific characteristics of orthogonal subcarriers to facilitate countermeasure. In particular, BatchAuth demonstrates significant potential on scalability in large-scale BC systems and multiple-input multiple-output (MIMO) systems. Theoretical analysis on BatchAuth security and extensive simulations under various settings by comparing with cutting-edge schemes further validate its commendable performance with regard to accuracy, robustness, efficiency, and scalability.

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.

Ambient backscatter communication (AmBC) enables ultra-low-power communications by backscattering ambient radio frequency (RF) signals and harvesting energy simultaneously. It has emerged as a cutting-edge technology for supporting a variety of Internet of Things (IoT) applications. However, existing research lacks effective secret key sharing schemes for safeguarding communications between resource-constrained backscatter devices (BDs) in AmBC systems. In this paper, we present, Tri-Channel, a novel physical layer key generation scheme between two BDs by multiplying downlink signals and backscatter signals to obtain the information of a triangle channel as a shared random secret source for key generation. In particular, we analyze the security of our scheme under both passive and active attacks, concretely Eavesdropping Attack (EA), Control Channel Attack (CCA), Signal Manipulative Attack (SMA), and Untrusted RF-Source Attack (URSA). Through theoretical analysis and simulations by comparing with a traditional scheme (named Tradi-Channel), we found that our scheme consistently outperforms the Tradi-Channel under the EA and two active attacks (CCA and SMA). In addition, it shows better security performance under URSA, which is proposed based on the unauthenticated characteristic of BDs in Tri-Channel, even though URSA is more vital than SMA. Concretely, Tri-Channel’s secret key rate (SKR) outperforms Tradi-Channel’s under the above four passive and active attacks. This implies that our scheme is advanced in terms of both security and efficiency of key generation. Numerous extensive simulations further prove our theoretical analysis results.