External Eavesdropper Research Articles

Encrypted Decentralized Multi-Agent Optimization for Privacy Preservation in Cyber-Physical Systems

Decentralized optimizations have been extensively applied in large-scale industrial cyber-physical systems to achieve control scalability. However, state-of-the-art methods heavily depend on explicit communications between participants, exposing the entire control framework to data confidentiality risks. To overcome this challenge, in this article, a privacy-preserving decentralized multi-agent cooperative optimization paradigm was developed via integrating cryptography into decentralized optimization. The proposed approach can effectively protect participants’ privacy against external eavesdroppers, honest-but-curious agents, and the system operator. Theoretical security and correctness analyses are provided. Simulations of numerical examples and experiments on a real-world platform are given to demonstrate the security, accuracy, and applicability of the proposed method.

Secure transmission in backhaul NOMA systems: A physical layer security design with untrusted user and eavesdropper

In order to improve the Physical Layer Security (PLS) perspective, this paper aims to empower function of PLS by considering a backhaul Non-Orthogonal Multiple Access (NOMA) system in two practical situations. In the proposed schemes, the untrusted user intercepts information transmitted to the far user, or the external eavesdropper overhears confidential information sent to the far user in the context of NOMA technique. Unlike the conventional NOMA systems, this paper emphasizes the actual situations of the existence of actual illegal users and legitimate users, especially the reasonable use of relay selection architecture to improve the confidentiality performance. To evaluate the security properties of the proposed scheme, a comprehensive analysis of the Security Outage Probability (SOP) performance is first performed, and then the corresponding SOP asymptotic expressions are derived for real scenarios related to eavesdroppers and untrusted users. Numerical results are performed to verify the analysis in terms of the secure performance metric.

Structural consensus in networks with directed topologies and its cryptographic implementation

The existing cryptosystem based approaches for privacy-preserving consensus of networked systems are usually limited to those with undirected topologies. This paper proposes a new privacy-preserving algorithm for networked systems with directed topologies to reach confidential consensus. As a prerequisite for applying the algorithm, a structural consensus problem is formulated and the solvability conditions are discussed for an explicitly constructed controller. The controller is then implemented with encryption to achieve consensus while avoiding individual’s information leakage to external eavesdroppers and/or malicious internal neighbors.

Maximizing the Secrecy Energy Efficiency of the Cooperative Rate-Splitting Aided Downlink in Multi-Carrier UAV Networks

Although Unmanned Aerial Vehicles (UAVs) are capable of significantly improving the information security by detecting the eavesdropper's location, their limited energy motivates our research to propose a secure and energy efficient scheme. Thanks to the common-message philosophy introduced by Rate-Splitting (RS), we no longer have to allocate a portion of the transmit power to radiate Artificial Noise (AN), and yet both the Energy Efficiency (EE) and secrecy can be improved. Hence we define and study the Secrecy Energy Efficiency (SEE) of a multi-carrier multi-UAV network, in which Cooperative Rate-Splitting (CRS) is employed by each multi-antenna UAV Base-Station (UAV-BS) for protecting their downlink transmissions against an external eavesdropper ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Eve$</tex-math></inline-formula> ). Furthermore, we consider the challenging scenario in which CRS is employed by each multi-antenna UAV-BS to protect their corresponding downlink transmissions against an external <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Eve$</tex-math></inline-formula> . We further consider a difficult scenario in terms of security in which only imperfect channel state information of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Eve$</tex-math></inline-formula> is available at the Tx. Accordingly, we conceive a robust secure resource allocation algorithm, which maximizes the SEE by jointly optimizing both the user association matrix and the network parameter allocation problem, including the RS precoders, time slot sharing and power allocation. Due to the non-convexity of the problem, it is decoupled into a pair of convex sub-problems. Firstly, new two-tier intra-cell optimization problems are formulated for achieving <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\xi$</tex-math></inline-formula> -optimal solutions by iterative block coordinate decent programming. Then, the power of each sub-channel is optimized by formulating the associated power control problem.

IRS-Aided Secure NOMA Networks Against Internal and External Eavesdropping

Intelligent reflecting surface (IRS) is a promising technology which can be integrated with non-orthogonal multiple access (NOMA) to improve the secrecy performance. In this paper, we propose two IRS-aided schemes to enhance the security of NOMA networks for the internal and external eavesdropping, respectively. First, to deal with an internal untrusted user, the secrecy rate maximization problem is formulated by jointly optimizing the active and passive beamforming, while meeting the quality of service (QoS) demand of the untrusted user, decoding order constraints, and unit modulus constraints of IRS elements. Furthermore, considering a worse scenario with both internal and external eavesdroppers, we minimize the transmit power of legitimate signals with both users’ QoS demands satisfied. In this way, the confidential information leakage will be mitigated and more transmit power can be allocated as artificial jamming to attenuate the eavesdropping. To tackle the non-convex optimization, the original problem in each scheme is first decomposed into two subproblems, which are approximated into convex ones via the semidefinite relaxation (SDR). Then, by means of alternating optimization, the suboptimal solutions to the original problems can be obtained. Simulation results demonstrate the superiority of the proposed schemes against the challenging internal and external eavesdropping by combining IRS and NOMA.

Quantization-Aided Secrecy: FD C-RAN Communications With Untrusted Radios

In this work, we study a full-duplex (FD) cloud radio access network (C-RAN) from the aspects of infrastructure sharing and information secrecy, where the central unit utilizes FD remote radio units (RU)s belonging to the same operator, i.e., the trusted RUs, as well as the RUs belonging to other operators or private owners, i.e., the untrusted RUs. Furthermore, the communication takes place in the presence of untrusted external receivers, i.e., eavesdropper nodes. The communicated uplink (UL) and downlink (DL) waveforms are quantized in order to comply with the limited capacity of the fronthaul links. In order to provide information secrecy, we propose a novel utilization of the quantization noise shaping in the DL, such that it is simultaneously used to comply with the limited capacity of the fronthaul links, as well as to degrade decoding capability of the individual eavesdropper and the untrusted RUs for both the UL and DL communications. In this regard, expressions describing the achievable secrecy rates are obtained. An optimization problem for jointly designing the DL and UL quantization and precoding strategies are then formulated, with the purpose of maximizing the overall system weighted sum secrecy rate. Due to the intractability of the formulated problem, an iterative solution is proposed, following the successive inner approximation and semi-definite relaxation frameworks, with convergence to a stationary point. Numerical evaluations indicate a promising gain of the proposed approaches for providing information secrecy against the untrusted infrastructure nodes and/or external eavesdroppers in the context of FD C-RAN communications.

Verifiable quantum secret sharing with multi access structures

In this paper, we propose a verifiable quantum secret sharing scheme. We share multi classical secrets by using the qudit state among the participants based on the different access structures. Moreover, it is possible to check the honesty of participants in the recovery phase. Analyses show that the proposed scheme is secure against internal and external eavesdroppers.

A Privacy-Preserving Distributed Control Strategy in Islanded AC Microgrids

As an effective method to improve the reliability, the advanced communication infrastructure also exposes the islanded AC microgrid (MG) to potential privacy threats. Although the existing differential-privacy based secondary controls provide the privacy protection through adding noise, the noise would bring about large harmonic components thereby degrading the power quality. To tackle with this problem, a novel integrated privacy-preserving distributed fixed-time (PDF) secondary control of the islanded AC MG is proposed for the accurate frequency restoration and active power sharing. The state decomposition strategy and the additional virtual proportional (AVP) coefficient are innovatively designed to achieve the privacy preservation, where the active power ratio of each DG is decomposed into several sub-states. The integrated PDF secondary control only requires each DG to transmit the first sub-state of active power ratio through communication network, which would not increase the communication burden. The designed privacy-preserving mechanism can protect the initial value and real-time running values simultaneously when the AVP coefficient is not disclosed to the external eavesdropper. The real-time simulations based on the NI-PXI real-time simulator are conducted to validate the effectiveness and advantages of the integrated PDF secondary control.

A Scheduling Scheme for Improving the Performance and Security of MU-MIMO Systems.

For the receiver of multiple-input multiple-output (MIMO) systems, linear detectors are an interesting option due to their good performance and low complexity. Nevertheless, MIMO systems lose diversity in exchange for eliminating interference when linear detectors are used. Aiming to maintain the system diversity while mitigating interference between users, this work proposes a scheduling scheme for the uplink of multiuser MIMO (MU-MIMO) systems that employ A antennas and the zero-forcing (ZF) detector at the receiver in the base station (BS). The channel model includes Rician fading and additive white Gaussian noise (AWGN) in an imperfect channel estimation scenario. The proposed scheme selects U users from a group of users to transmit simultaneously, so that the signal-to-noise ratio (SNR) is maximized. For this, an exact expression to evaluate the SNR of the users is obtained. With this result, the scheduling strategy is proposed. Results show that as increases, the outage probability (OP), and the bit error rate (BER) decrease as the system diversity increases, even when the system is completely loaded, i.e., when . Moreover, it is shown that the scheduling scheme counteracts the imperfect channel estimation effects as increases. Finally, the proposed scheme is tested in presence of an external eavesdropper trying to decode the information sent by the users. The results show that the presented proposal allows for a reduction of the secrecy-outage-probability (SOP) as increases.

Jammer-Assisted Secure Precoding and Feedback Design for MIMO IoT Networks

Great concerns on the Internet of Things (IoT) security are raised as IoT becomes an emerging paradigm to achieve ubiquitous connectivity. This article studies low-complexity secure transceiver and feedback design with the assistance of a jammer for physical-layer security in multiantenna IoT systems. We consider the general setting where a legitimate multiantenna controller broadcasts confidential messages to multiple multiantenna IoT devices in the presence of a passive external multiantenna eavesdropper. Moreover, there is only quantized downlink channel state information (CSI) at the controller and the jammer through feedback channels. We introduce several secure transceivers for different system setups, all of which employ block-diagonal precoding at the controller and null-space beamforming at the jammer but are with the different receivers at each IoT device. Considering the practical setup of IoT and for the tractability of analysis, we study the secrecy performance of the transceiver with an arbitrarily selected receive matrix independent of the channels of all devices. We derive an approximate lower bound on the ergodic secrecy rate (ESR) of each device <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">without</i> assuming any asymptotes for system parameters. The obtained result can also be viewed as a lower bound on the ESR performance of any other transceivers. We also optimize this bound to find an adaptive feedback bit allocation to the two feedback channels of each legitimate device. Numerical results are shown to illustrate the obtained analytical ESR lower bound, the feedback bit allocation algorithm, and significant ESR performance gain that results from the proposed feedback bit allocation.

Distributed privacy-preserving electric vehicle charging control based on secret sharing

Cooperative electric vehicle (EV) charging control has emerged as a key component in grid-edge resource (GER) management. However, customers’ privacy remains a major barrier to large-scale implementation of EV charging control. In this paper, we develop a distributed privacy-preserving EV charging control protocol based on secret sharing (SS) that (1) achieves scalability over EV population size; (2) enjoys higher computation efficiency compared to homomorphic encryption (HE) based methods; and (3) secures the privacy of the participating EVs against honest-but-curious adversaries and external eavesdroppers. The cooperative EV charging control is formulated to achieve overnight valley filling and framed into the projected gradient algorithm (PGA) structure as a distributed optimization problem. SS is integrated into PGA to achieve secure updates of both primal and dual variables. Theoretical security analyses and simulations in a residential area are conducted to prove the privacy preservation guarantee as well as the efficacy and efficiency of the proposed privacy preservation method. Broadly, the proposed method can be readily extended to various GER control applications.

Privacy Preservation of Optimization Algorithm Over Unbalanced Directed Graph

This paper proposes an algorithm with the property of privacy preservation to solve the multi-agent optimization problem, where the communication topology is a fixed and strongly connected directed graph with a row stochastic weight matrix. Here, we consider the external eavesdropper attack model and take the gradient information of the objective function as the agent's privacy information. In this algorithm, each agent adds an additional state variable that interacts with it with a time-varying weight. And this new variable performs gradient iterative calculation. The original state variable interacts with the new variable and the original neighbors. It is proved that the algorithm converges to the optimal solution of the problem and at the same time achieves the purpose of privacy preservation. In addition, the algorithm neither requires additional hidden signals, nor does it increase a large amount of calculation. Finally, a simulation example is given to verify the performance of the algorithm.

Performance Evaluation and Security Analysis of UAV-Based FSO/CV-QKD System Employing DP-QPSK/CD

Unmanned aerial vehicles (UAV) based on free-space optical (FSO) systems combine the benefits of both the high data rate of the FSO and the mobility of UAV. However, cumulative effects of laser beam divergence and turbulence-induced fading on the received irradiance in the FSO link might allow an external eavesdropper located near the authorized receiver to break the transmission under certain conditions. Quantum key distribution (QKD) is a technique of secure communication that employs quantum mechanics-based cryptography principles. A combination of a continuous-variable quantum key distribution (CV-QKD) and Gaussian modulation of quantum coherent states (GMCS) enables a relatively secure communication system against collective attacks over FSO transmission links. However, the performance is restricted and degraded due to the influence of atmospheric turbulence and excess noise. This paper aims to evaluate the performance of a secured UAV-based FSO system utilizing prepare and measure CV-QKD protocol based on GMCS under collective attack in terms of quantum bit error rate (QBER), outage probability, and secret key rate (SKR) considering the impairments of the FSO channel, link budget, deviations in the position and attitude angles of the UAV, channel fluctuating transmittance, and excess noise. The system parameters, including transmit power, receiver’s field-of-view, and beam divergence angle, are optimized to satisfy the system’s design criteria of threshold-QBER <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$=10^{-3}$</tex-math></inline-formula> and threshold outage probability <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$=10^{-2}$</tex-math></inline-formula> . The proposed system tolerates boresight displacement up to 7 cm with the optimized values. The Closed-form expressions and analytical results are confirmed by Monte-Carlo simulations.

Safeguarding Non-Orthogonal Multiple Access with Physical Layer Techniques

This article clarifies pivotal security issues in the context of non-orthogonal multiple access (NOMA) technology and presents potential methodologies to address them at the physical layer. Specifically, we first clarify the channel conditions for an external eavesdropper to use successive interference cancellation (SIC) for cancelling interference, which has recently been considered in the literature of physical layer security for NOMA. We then explicitly demonstrate the advantages and drawbacks of using NOMA to achieve wireless communication security; that is, NOMA improves the security of a strong user, but reduces the security of a weak user. Finally, we discuss a strategy to protect the confidentiality of a weak user's information from a strong user, while still allowing the latter to seek SIC for harnessing the benefits of NOMA. Research challenges and future works along the aforementioned three different aspects of security issues in NOMA are presented in this article.

A secure crossing two qubits protocol based on quantum homomorphic encryption

In order to solve the information leakage caused by dishonest intermediate nodes in quantum network coding, we apply quantum homomorphic encryption to the butterfly network, and propose a secure protocol for crossing two qubits. Firstly, in the communication process between two senders and the first intermediate node, two senders encrypt their measured particles and send them to the first intermediate node for encoding. If two intermediate nodes are dishonest and know the encryption rules between two senders and two receivers, or there is an external eavesdropper, none of them can recover the transmitted qubits of two senders from the encrypted transmitted particles. In this way, our protocol can transmit two qubits safely and crossly in the butterfly network. Secondly, by analyzing the internal participant attack and the external eavesdropper attack launched by dishonest intermediate nodes and an external eavesdropper respectively, it is confirmed that our protocol is secure. Finally, the experimental simulation results based on the Qiskit framework prove that our protocol is feasible.

Privacy-preserved average consensus algorithms with edge-based additive perturbations

In this paper, we consider the privacy preservation problem in continuous-time average consensus algorithms with strongly connected and balanced graphs, against either internal honest-but-curious agents or external eavesdroppers. A novel algorithm is proposed, which adds edge-based perturbation signals to the process of consensus computation. Our algorithm can be divided into two phases: a coordinated scrambling phase, which is for privacy preservation, and a convergence phase. In the scrambling phase, each agent is required to generate some perturbation signals and add them to the edges leading out of it. In the convergence phase, the agents update their states following a normal updating rule. It is shown that an internal honest-but-curious agent can obtain the privacy of a target agent if and only if no other agents can communicate with the target agent. As for external eavesdroppers, it is proved that this kind of attackers can never obtain any agent’s privacy.

Splitting an Arbitrary Three-Qubit State via a Five-Qubit Cluster State and a Bell State.

Quantum information splitting (QIS) provides an idea for transmitting the quantum state through a classical channel and a preshared quantum entanglement resource. This paper presents a new scheme for QIS based on a five-qubit cluster state and a Bell state. In this scheme, the sender transmits the unknown three-qubit secret state to two agents by the quantum channel with the Bell basis measurement three times and broadcasts the measurement results to the agents through the classical channel. The agent who restores the secret state can successfully recover the initial information to be transmitted through the appropriate unitary operation with the help of the other party. Firstly, our scheme’s process can be accurately realized by performing the applicable Bell basis measurement, single-qubit measurement, and local unitary operation instead of a multiparticle joint measurement. The splitting process of quantum information is realized through a convenient operation. Secondly, compared with some previous schemes, the efficiency of the total scheme has been improved in principle, and the qubit consumption is reduced. Finally, the security of the quantum information splitting scheme is analyzed from the perspectives of external attacks and participant attacks. It is proved that our scheme can effectively resist internal participant attacks and external eavesdropper attacks.

Privacy-preserving dynamic average consensus via state decomposition: Case study on multi-robot formation control

Dynamic average consensus is a decentralized control/estimation framework where a group of agents cooperatively track the average of local time-varying reference signals. In this paper, we develop a novel state decomposition-based privacy preservation scheme to protect the privacy of agents when sharing information with neighboring agents. Specifically, we first show that an external eavesdropper can successfully wiretap the reference signals of all agents in a conventional dynamic average consensus algorithm. To protect privacy against the eavesdropper, a state decomposition scheme is developed where the original state of each agent is decomposed into two sub-states: one succeeds the role of the original state in inter-node interactions, while the other sub-state only communicates with the first one and is invisible to other neighboring agents. Rigorous analyses are performed to show that (1) the proposed privacy scheme preserves the convergence of the average consensus; and (2) the privacy of the agents is protected such that an eavesdropper cannot discover the private reference signals with guaranteed accuracy. The developed privacy-preserving dynamic average consensus framework is then applied to the formation control of multiple non-holonomic mobile robots, in which the efficacy of the scheme is demonstrated. Numerical simulation is provided to illustrate the effectiveness of the proposed approach.

A Simple Data Privacy and Security Protection Algorithm Based on Federated Learning

Although federated learning can break the data island and enhance privacy, it is not absolutely secure. External eavesdroppers can intercept the model when clients upload their models to the server, which might be used to infer the data information. A natural solution is to add noise to the uploaded model. However, this solution has its drawback, because the added noise cannot be eliminated when the models are aggregated at the server, which leads to poor performance. In order to tackle this problem, we propose a simple but effective algorithm, FedNoise. In the vanilla federated learning algorithm, a gradually decreasing learning rate is applied at the client side. While in our algorithm, we divide the parameter update into client-side and server-side. The stochastic gradient descent update with constant learning rate is performed at the client side and a gradually decreasing learning rate is performed at the server. Our algorithm can not only ensure the data security, but also maintain comparable system performance. Simulation results validate our conclusion.

Secure reconfigurable intelligent surface aided heterogeneous VLC–RF cooperative NOMA networks

In this paper, we investigate the physical layer security for a reconfigurable intelligent surface (RIS)-aided heterogeneous visible light communication (VLC) and radio-frequency (RF) network with two legitimate user equipments (UEs) in cooperative nonorthogonal multiple access (NOMA). An external eavesdropper (Eve) tries to eavesdrop the information from the cooperative channel. Since VLC is mainly available for line-of-sight path, and the UEs and Eve under the worktable cannot directly receive signals from the optical access point, a device is naturally employed to perform optical–electrical conversion and RF transmission. Further the device and RIS are jointly employed to eliminate blind spots and extend communication coverage. With these settings, the statistical characteristics of the VLC link and RF link are determined based on the feature of the optical channel and the RIS-aided wireless channel, respectively. The close-form expression of the secrecy outage probability for the proposed RIS-aided heterogeneous VLC–RF cooperative NOMA network is derived. Simulation results show the secrecy outage performance of the proposed network depends on not only the reflecting meta-surface number of the RIS, the power allocation based on NOMA, but also the tradeoff design between the optical and electrical parameters.