Untrusted Relay Node Research Articles

Cooperative Jamming-Assisted Untrusted Relaying Based on Game Theory for Next-Generation Communication Systems

In this contribution, we investigate the performance of an untrusted relaying system when Cooperative Jammers (CJs) are available. We propose two scenarios, Untrusted Relaying-aided Multiple Cooperative-Jammers-based Simultaneous Transmission (UR-MCJST) and an Untrusted Relaying-aided Multiple Cooperative Jammers-based Time-Division Transmission (UR-MCJTDT). The performances of both UR-MCJST and UR-MCJTDT schemes are investigated. The source node is the primary user (PU) that has access to a transmission bandwidth. An untrusted relay is employed for improving the reliability of the PU transmission, while CJs are invoked for improving the secrecy rate of the PU transmission. The transmission strategy for the scheme proposed in this paper is split into three unique phases. The first phase is called the broadcast-and-jamming phase, while the second phase is called the relaying phase, and the final phase is called CJ’s secondary phase, which is used for transmitting the secondary user message. More explicitly, CJs transmit noise for impairing the untrusted relay node’s ability to decode the message during the broadcast-and-jamming phase. In compensation for their help, CJs are allocated part of the available spectrum by the PU for their transmission during the secondary transmission phase. A Stackelberg leader–follower game was considered between the PU and the CJs, while a power control game that is based on the well-known Nash equilibrium is employed by the CJs. Furthermore, an investigation into the effect of invoking simultaneous transmission and time-division-based transmission scenarios during the CJs’ secondary transmission phase was carried out. Finally, we evaluated the achievable secrecy rate of the PU and the utility rate of the CJs in our proposed scheme.

Topology-Abstraction-Based Protection Scheme in Quantum Key Distribution Networks with Partially Trusted Relays

Quantum key distribution (QKD) can protect the exchange process of confidential information between communicating parties. By using the basic principles of quantum mechanics and combined with “one-time pad” cipher encryption, information can be unconditionally secure. The BB84 protocol first describes the method of transmitting information by photon polarization state, and it expounds the transmission process of services between trusted relays. However, due to the defects of real experimental devices, there are security vulnerabilities in QKD in a real system. The birth of measurement-device-independent quantum key distribution (MDI-QKD) protocol solves the problem, providing immunity to hacker attacks at the end of the detector. It can enable both sides of the transmission service to establish a connection and generate secret keys through an untrusted relay node to ensure information security. However, the types and properties of link nodes in quantum key distribution network (QKDN) based on partially trusted relay are more complex, which can easily result in network fault. Therefore, how to prevent the impact of failure on QKDN has become an urgent problem. In this paper, we propose a protection scheme for QKDN with partially trusted relays. The method deals with trusted and untrusted relays differently and constructs the working and protection paths of the secret key for each service. It reduces resource conflict between the protection and working paths by establishing a key protection threshold, which realizes the resource trade-off between the two factors. Simulation results show that the scheme provides effective protection to the services, and it improves the stability and reliability of QKDN based on partially trusted relay.

Impact of Outdated CSI on the Secure Communication in Untrusted In-Band Full-Duplex Relay Networks

To provide reliable connectivity in recent and future wireless communication systems, it is necessary to deploy several relay nodes. Further, a full-duplex (FD) technique has been in the spotlight since it can significantly improve spectral efficiency, and thus recent studies in relaying networks have considered FD relays. In relaying networks, confidentiality between the source and destination nodes from the relay node should be carefully kept since the relay node cannot be fully trusted, so called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">untrusted</i> relay node. To this end, in this paper, we consider physical-layer security taking into account an untrusted FD relay node. We investigate a secure relaying protocol against the untrusted relay node where the destination generates artificial noise to prevent the untrusted relay from decoding the source information. We derive the analytical expression of the lower bound of the ergodic secrecy rate ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bar {R}$ </tex-math></inline-formula> ). We find two main factors affecting the secrecy performance: residual self-interference (RSI) at the FD-available nodes (i.e., relay and destination), and outdated channel state information (CSI) at the destination. Thereafter, we evaluate their effects on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bar {R}$ </tex-math></inline-formula> and suggest the algorithm to find the sub-optimal artificial noise power level at the destination for maximizing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bar {R}$ </tex-math></inline-formula> . Through simulations, we have verified our mathematical derivation and shown that our secure relaying protocol can achieve near-optimal secrecy performance. Numerical results imply that the artificial noise power level should be carefully considered when the channel is severely outdated and RSI is irresistible.

Secrecy rate maximization for hardware impaired untrusted relaying network with deep learning

This paper investigates the physical layer security (PLS) design of an untrusted relaying network where the source node coexists with a multi-antenna eavesdropper (Eve). While the communication relies on untrustworthy relay nodes to increase reliability, we aim to protect the confidentiality of information against combined eavesdropping attacks performed by both untrusted relay nodes and Eve. Considering the hardware impairments (HIs), both total power budget constraint for the whole network and the individual power constraint at each node, this paper presents a novel approach to jointly optimize relay beamformer and transmit powers aiming at maximizing average secrecy rate (ASR). To safeguard the first cooperative phase, destination-aided cooperative jamming (DACJ) is employed, while for the second phase, the relay beamformer is adjusted. The resultant optimization problem is non-convex, and a suboptimal solution is obtained through the sequential parametric convex approximation (SPCA) method. In order to prevent any failure due to infeasibility, we propose an iterative initialization algorithm to find the feasible initial point of the original problem instead of an arbitrary point, as in the conventional SPCA. To satisfy low-latency as one of the main key performance indicators (KPI) required in beyond 5G (B5G) communications, a computationally efficient data-driven approach is developed exploiting a deep learning model to evaluate the proposed scheme while the computational burden is significantly reduced. Simulation results assess the effect of different system parameters on the ASR performance as well as the effectiveness of the proposed deep learning solution in large-scale cases.

Secrecy Performance of a Multi-NOMA-MIMO System in the UEH Relaying Network Using the PSO Algorithm

In this paper, we investigate the secrecy performance of the nonorthogonal multiple access (NOMA) system in an untrusted relaying energy harvesting (UEH) network with the multiple-input multiple-output (MIMO) architecture using the maximum ratio transmission (MRT) and maximal ratio combining (MRC) techniques. In this network, a source communicates with users with the help of a relaying network composed of multiple untrusted components using the amplify-and-forward (AF) protocol. These untrusted relay nodes are equipped with a single antenna and employ the power-splitting (PS) protocol to harvest energy from received signals. Moreover, to improve the secrecy outage performance and protect the confidential information from the untrusted relaying network, the source acts as the jammer to generate artificial noise (AN). To evaluate the secrecy performance of each user and the overall system, we derive the closed-form expressions of the secrecy outage probability (SOP) over the Rayleigh fading channels and use a Monte Carlo simulation to verify the accuracy of these analytical results. Moreover, to analyze the secrecy data rate, the maximization problem of the sum secrecy rate (SSR) of the system is solved by applying the particle swarm optimization (PSO) algorithm based on power allocation (PA). These results are also validated with the optimal exhaustive search method. Furthermore, we compare the MIMO/NOMA and MIMO/OMA systems and examine the effects of various system parameters to characterize the secrecy effectiveness of both systems.

Simultaneous two-way classical communication and measurement-device-independent quantum key distribution with coherent states

Simultaneous quantum and classical communication integrates both continuous variable quantum key distribution and classical coherent optical communication by using the same communication infrastructure. Given its compelling benefits, we proposed a protocol relying on both two-way classical communication and on measurement-device-independent quantum key distribution, in which the superposition-modulation-based coherent states depend on the information bits of both the secret key and on the classical communication ciphertext, which are measured by an untrusted relay node. The proposed scheme strikes a beneficial balance between its level of security and its grade of practicability. Explicitly, on the one hand, the secret key obtained is secure against all attacks on the detectors, and it is eminently suitable for bidirectional classical communication in the metropolitan network as a benefit of its relay-based configuration. Our results show a convincing bit error rate vs secret key rate trade-off for transmission over dozens of kilometers in the quantum channel, hence striking an excellent integrity (bit error rate) vs security trade-off.

On the Secrecy Performance and Power Allocation in Relaying Networks With Untrusted Relay in the Partial Secrecy Regime

Recently, three useful secrecy metrics based on the partial secrecy regime were proposed to analyze secure transmissions on wireless systems over quasi-static fading channels, namely: generalized secrecy outage probability, average fractional equivocation, and average information leakage. These metrics were devised from the concept of fractional equivocation, which is related to the decoding error probability at the eavesdropper, so as to provide a comprehensive insight on the practical implementation of wireless systems with different levels of secrecy requirements. Considering the partial secrecy regime, in this paper we examine the secrecy performance of an amplify-and-forward relaying network with an untrusted relay node, where a destination-based jamming is employed to enable secure transmissions. In this regard, a closed-form approximation is derived for the generalized secrecy outage probability, and integral-form expressions are obtained for the average fractional equivocation and the average information leakage rate. Additionally, equal and optimal power allocation schemes are investigated and compared for the three metrics. From this analysis, we show that different power allocation approaches lead to different system design criteria. The obtained expressions are validated via Monte Carlo simulations.

Asymmetric Protocols for Scalable High-Rate Measurement-Device-Independent Quantum Key Distribution Networks

Measurement-device-independent quantum key distribution (MDI-QKD) can eliminate detector side channels and prevent all attacks on detectors. The future of MDI-QKD is a quantum network that provides service to many users over untrusted relay nodes. In a real quantum network, the losses of various channels are different and users are added and deleted over time. To adapt to these features, we propose a type of protocols that allow users to independently choose their optimal intensity settings to compensate for different channel losses. Such protocol enables a scalable high-rate MDI-QKD network that can easily be applied for channels of different losses and allows users to be dynamically added/deleted at any time without affecting the performance of existing users.

Securing Untrusted Full-Duplex Relay Channels in the Presence of Multiple External Cluster-Based Eavesdroppers

We investigate the physical layer security of a wireless cooperative network where communication between Alice and Bob is assisted by a full-duplex (FD) untrusted relay, Ray, in the presence of multiple external eavesdroppers, Eves. A cluster-based colluding eavesdropping setting is considered, where illegitimate nodes with common interests are grouped in a cluster. To confuse the different eavesdropping clusters, we employ artificial-noise (AN) aided beamforming at the source node. Moreover, FD relay jamming is used to improve the system's security. To maintain secure communications against the untrusted relay node, an FD destination jamming scheme is adopted. Our proposed scheme is designed based on the channel state information of the legitimate nodes only. We optimize the transmit power allocation factors between data and AN signals, the data and AN precoders at Alice, the AN precoder at Bob, and the data and AN precoders at Ray. Numerical results show that the optimal power allocation factor between data and AN depends on the total number of antennas of the different colluding eavesdropping clusters.

Polarization-based plug-and-play measurement-device-independent quantum key distribution

Measurement-device-independent quantum key distribution (MDI-QKD) has received much attention, with the goal of overcoming all of the security loopholes caused by an imperfect detection system. We here propose a plug-and-play MDI-QKD (P&P MDI-QKD) scheme whereby an untrusted relay node, Charlie, owns a laser and sends photons to Alice and Bob. Alice (Bob) modulates the polarization of the incident photons and returns them to Charlie. Charlie uses a modified Bell state analyzer (BSA) to perform Bell state measurements (BSM). In comparison with the original version of MDI-QKD, our scheme exploits a single untrusted laser as the photon source. This makes the signal photons identical and enhances the Hong-Ou-Mandel effect. Second, because of the P&P structure, the setup can automatically eliminate the birefringence influence of the fibers, which makes the setup highly stable. Finally, our modified BSA can identify $${{\left| \varPhi \right\rangle }^{+}}$$ and $${{\left| \varPhi \right\rangle }^{-}}$$ of four Bell states with polarization encoding but not $${{\left| \varPsi \right\rangle }^{+}}$$ and $${{\left| \varPsi \right\rangle }^{-}}$$ . Based on practical experimental parameters, a simulation showed that the maximum theoretical secure transmission distance could reach more 280 km.

Secrecy Transmission for Self-Energy Recycling Untrusted Relay Networks With Imperfect Channel State Information

For the self-energy recycling (SER) untrusted relay network, a two-phase destination-based jamming (DBJ) protocol is proposed, in which the destination transmits the jamming signal to reduce the received SNR of the untrusted relay node in the first phase and the relay node operated in full-duplex (FD) mode for simultaneous energy transfer and information relaying in the second phase. In addition, the loopback interference (LI) generated by FD relay node can be reused as part of energy. To satisfy some practical application scenarios, we consider the imperfect channel estimation error at the destination. Considering the total power constraint and the quality of service (QoS) requirement at the destination, the secrecy rate maximization problem is formulated by optimizing the transmission power of source and destination. However, the formulated problem is non-convex and difficult to solve directly. To cope with this difficulty, an iterative power allocation algorithm is proposed. The key idea of the proposed algorithm first integrates the non-convex constraint into the objective function by the exact penalty method. Then the difference of convex functions (DC) programming can be utilized to convert the non-convex objective function into the approximate convex function and the sub-optimal transmission power of source and destination can be obtained by the traditional convex programming. Simulation results show the superiority security performance of the proposed scheme with the traditional schemes.

Adaptive Secure Transmission for RF-EH Untrusted Relaying with Alien Eavesdropping

An adaptive cooperative scheme is proposed to improve the security of a wireless-powered relay network. A source node sends data to a destination node in the presence of an amplify-and-forward untrusted relay node and an alien eavesdropper where both are assumed to attempt to decode the source’s information signal. The source uses a fraction of its transmit power to send a jamming signal to keep its information confidential. To save energy, the energy-harvesting relay node transmits with the minimum power level that ensures secure transmissions. We derive a closed-form upper bound on the system’s secrecy outage probability. The proposed cooperative scheme is more efficient than the conventional scheme, where once the relay has accumulated sufficient energy, it assists the source’s information transmission.

Multi-Terminal Two-Hop Untrusted-Relay Networks With Hierarchical Security Guarantees

We consider a two-source two-destination two-hop relay network, where all data communication must be kept secret from the relay node. The model considered is the simplest primitive that embodies a multi-transmitter multi-receiver network that needs to communicate sharing an untrusted relay node. We focus on two scenarios. In the first scenario, each source aims to send two messages to be kept secret from the relay: a common message that should be decoded by both destinations, and a private message that should be decoded by the first destination while kept secret from the second one. We define an achievable rate region by utilizing stochastic encoding at the sources, the Gaussian noise cooperative jamming from the destinations, and compress-and-forward at the relay. In the second scenario, each source aims to send a confidential message to its intended destination, which should be kept secret from the other one as well as the relay. We define an achievable rate region using a combination of nested lattice codes and random binning at the sources, structured cooperative jamming from destinations, and scaled compute-and-forward at the relay. We also derive genie-aided outer bounds on the secrecy rate regions. We present numerical results that demonstrate the performance of the proposed achievable schemes. Overall, this paper provides insights into how to utilize an untrusted relay to communicate to destinations with different levels of security clearance, and how intentional interference is an enabler of communication.

Robust Relay in Narrow-Band Communications for Ubiquitous IoT Access

We propose a robust wireless relay scheme in narrow-band communications for IoT access, which matches the typical features of IoT often carrying relatively low data rate with limited bandwidth. This framework is towards offering robustness in QoS guarantees with emphases on security and/or reliability, and we use the security-assured network as the typical scenario. In particular, we consider a dual-hop relay network including a transmitter, a receiver, an amplify-and-forward (AF) untrusted relay, and a jamming node. The jamming node is treated as a helper. Specifically, the jammer broadcasts artificial noise (AN), which in fact pollutes both the untrusted relay and the destination node’s signals. However, we show that such AN can be effectively mitigated after the destination node obtains the forwarded signal from the relay, while the untrusted relay node cannot do so. The core idea for robustness assurance is to exploit higher signal dimensions at the receiver over the untrusted relay node. Simulations and analyses are also conducted to demonstrate that our proposed scheme can make the performance at the untrusted relay an interference-limited manner while completely removing the interferences at the receiver, therefore corroborating our claim in robustness in terms of security and reliability.

Securing Untrusted RF-EH Relay Networks Using Cooperative Jamming Signals

We propose a new scheme to secure a wireless-powered untrusted cooperative-communication network, where a legitimate source node (Alice) transmits her information messages to a legitimate destination node (Bob) through the multiple amplify-and-forward untrusted relays. The relay nodes are assumed to be honest but curious nodes; hence, they are trusted at the service level but are untrusted at the information level. To reduce the energy consumption of the network, only one relay node is selected in each time slot to forward Alice’s information signal. We assume a power-splitting-based energy-harvesting scheme, where each relay node splits its received signal into information and energy streams. Since the relay nodes are assumed to be untrusted at the information level, they attempt to decode the information intended to Bob while harvesting energy at the same time. When the relaying mode is selected, the scheme is realized over two non-overlapping time phases. To prevent any information leakage to the untrusted relay nodes, Bob and a cooperative jammer (John) inject jamming (artificial noise) signals during the first phase. During the second phase, the untrusted relay nodes that will not be forwarding the information signal must harvest energy to accumulate more energy to help Alice in future time slots. Moreover, the cooperative jammer will jam the untrusted relays to further power their batteries and prevent them from decoding the information-forwarding relay signal in case they decided to cheat and decode it. We model the battery state transitions at each relay as a finite-state Markov chain and analyze it. Our numerical results show the security gains of our proposed scheme relative to two benchmark schemes.

Secrecy Analysis of Multiuser Untrusted Amplify-and-Forward Relay Networks

This paper investigates the secure communications of multiuser untrusted amplify-and-forward relay networks in the presence of direct links. In the considered system, one user is selected among multiple ones for secure transmission to the destination node with the help of an untrusted relay node. To reduce the information leakage to the untrusted relay, the paper considers two selection criteria to select the user based on the direct and the relaying links, respectively. The impact of direct and the relaying link on the system secrecy performance is studied by deriving the close-form ergodic secrecy rate (ESR) as well as the asymptotic expression. From the asymptotic expression, it can be found that the asymptotic ESR increases linearly with the logarithm of the average channel gain ratio of the direct link to the relaying link.

EE‐RS and PA for untrusted relay network at high signal‐to‐noise ratio regime

In this study, the authors investigate the energy-efficient (EE) relay selection (RS) and power allocation (PA) in a cooperative secured system. Their scenario includes a multiple-antenna source, a multiple-antenna destination and multiple amplify-and-forward untrusted relay nodes, where the relay nodes only have the channel-amplitude information. To prevent the untrusted relays from intercepting the source message and to achieve positive secrecy rate, the destination-based cooperative jamming technique is used. By maintaining a minimum required secrecy rate, three optimal joint RS and power minimisation schemes are studied. The first objective is minimising the total transmit power consumption, and therefore obtaining the corresponding EE-RS and PA schemes. Second, they focus on relay power minimisation, and third sum power minimisation of the relay and one mobile node by considering a weighted factor are investigated. Closed-form solutions are presented for three practical optimised networks. Finally, some numerical results are provided to show the merits of the proposed scheme. They also give some insights to system design.

Relay Selection for Secure Successive AF Relaying Networks With Untrusted Nodes

In this paper, the security aspect of an amplify-and-forward relaying network with untrusted relay nodes is considered. The untrusted nodes can help to forward the received signal and they may also try to decode such information, which can be regarded as potential eavesdroppers (Eves). To deal with such a challenging issue, a successive relaying scheme is adopted, where the multi-antenna source transmits to two selected nodes alternately, and the conventional detrimental inter-relay interference is used to jam the untrusted nodes without external helpers. Considering different complexity requirements, several relay selection schemes are proposed, and the closed-form expressions of the lower bound of secrecy outage probability are derived accordingly. To obtain some insights for the network design, an asymptotic analysis is also given, which shows that the maximum secrecy diversity order of $N-1$ can be achieved, where $N$ is the number of the untrusted relays. Moreover, the spectral efficiency is improved dramatically with the successive relaying scheme. Simulation results show that the proposed max–min scheme has almost the same performance as that of the optimal one, and the theoretical results match well with the simulation results.

SNR based secure communication via untrusted amplify-and-forward relay nodes using artificial noise

A two-phase beamforming solution for secure communication using untrusted relay nodes is presented. To thwart eavesdropping attempts of participant relay nodes, we deliberately introduce artificial noise in the source message. We observe that for certain scenarios, the source node prefers to allocate its full power to the message signal and, therefore, in the absence of artificial noise, such transmissions will be vulnerable to eavesdropping. Therefore, we provide a signal-to-noise ratio (SNR) based framework for secure communication. We intend to bring down the SNR at each of the untrusted relay nodes below a certain predefined threshold; whereas, using beamforming, we want to boost the SNR at the destination. With this motive, we evaluate the optimal scaling vector for the beamforming phase, which not only nullifies the artificial noise transmitted initially, but also maximizes the SNR at the destination. We discuss both the total and individual power constraint scenarios and provide an analytical optimal solution and an iterative algorithm, respectively.

Joint optimal power allocation and relay selection to establish secure transmission in uplink transmission of untrusted relays network

In this paper, the authors deal with secure transmission in two-hop amplify-and-forward network with untrusted relays. To prevent the untrusted relays from intercepting the source message and to achieve positive secrecy rate, the destination-based cooperative jamming technique is used. The authors propose joint secure best relay selection (BRS) and optimal power allocation (OPA) for uplink transmission of a cellular network when the base station is equipped with very large-scale antenna arrays. Then, the common performance metrics such as ergodic secrecy rate (ESR) and secrecy outage probability are evaluated for the optimised network. Moreover, the diversity order and diversity-multiplexing tradeoff of the system are examined. The authors obtain that the diversity order of joint BRS and OPA scenario is equal to number of relays. Finally, some numerical and simulation results are presented to validate the theoretical analysis and to show the advantages offered by the presented systems. They reveal interesting results that, by increasing number of untrusted relay nodes, the system performance improves. For example, for target ESR 2 bits/s/Hz and ten untrusted relay nodes, the optimised network saves about 5 dB for uplink transmission, in comparison with the system applying the BRS and equal power allocation.