Eavesdropping Strategies Research Articles

Waveguide Eavesdropping Threat for Terahertz Wireless Communications

As wireless communications move to higher frequency band for 5G networks and beyond, resiliency against eavesdropping and other security threats is still one of the key system-design considerations. Compared to data transmissions by lower frequencies, terahertz links are inherently more robust against eavesdropping attacks due to their propagation characteristics (such as high free-space path loss) and aligned link path by high-gain antennas. However, it does not indicate that eavesdropping is always impossible. Line-of-sight terahertz links have proven to be vulnerable to active/passive eavesdroppers by placing scatters in the path of data transmission, or by collecting side-lobe leakages. Here, we demonstrate a waveguide-based approach for signal eavesdropping which can be operated much more feasibly with several advantages, such as lower propagation loss and reliable data interception. Our method relies on a 3D printed rectangular dielectric waveguide and can overcome spatial limitations caused by directional modulation or near-field modulation. We demonstrate successful eavesdropping attacks for a 16 quadrature amplitude modulated (16-QAM) data link at rates up to 5 gigabits per second. Our work highlights the importance of system designs in resisting waveguide-based eavesdropping strategies and identifies aspects where

Integrated semi‐quantum layered communication

AbstractIn recent times, secure quantum communication in layered networks has emerged as an important area of study. The authors harness the potential offered by multidimensional states in secure quantum communication with only one quantum participant and all the other classical participants. Three protocols are proposed for—(i) entanglement‐based layered semi‐quantum key distribution, (ii) layered semi‐quantum secret sharing, and (iii) integrated layered semi‐quantum key distribution and secret sharing to share secret information in arbitrarily layered networks. These protocols integrate the features of semi‐quantum communication in layered networks. All three protocols allow for simultaneous distribution of secure information in all the layers of a network, thanks to the employment of multidimensional states. These protocols are presented for a small network of at most five participants and three layers and show the robustness of the same against various eavesdropping strategies. Finally, a detailed procedure is provided for generalisations of the proposed protocols to distribute keys/secrets in any arbitrarily structured quantum network.

Improved device-independent randomness expansion rates using two sided randomness

A device-independent randomness expansion (DIRE) protocol aims to take an initial random string and generate a longer one, where the security of the protocol does not rely on knowing the inner workings of the devices used to run it. In order to do so, the protocol tests that the devices violate a Bell inequality and one then needs to bound the amount of extractable randomness in terms of the observed violation. The entropy accumulation theorem lower bounds the extractable randomness of a protocol with many rounds in terms of the single-round von Neumann entropy of any strategy achieving the observed score. Tight bounds on the von Neumann entropy are known for the one-sided randomness (i.e. where the randomness from only one party is used) when using the Clauser–Horne–Shimony–Holt game. Here we investigate the possible improvement that could be gained using the two-sided randomness. We generate upper bounds on this randomness by attempting to find the optimal eavesdropping strategy, providing analytic formulae in two cases. We additionally compute lower bounds that outperform previous ones and can be made arbitrarily tight (at the expense of more computation time). These bounds get close to our upper bounds, and hence we conjecture that our upper bounds are tight. We also consider a modified protocol in which the input randomness is recycled. This modified protocol shows the possibility of rate gains of several orders of magnitude based on recent experimental parameters, making DIRE significantly more practical. It also enables the locality loophole to be closed while expanding randomness in a way that typical spot-checking protocols do not.

Quantum and Semi–Quantum key Distribution in Networks

In this paper, we utilize the potential offered by multidimensional separable states (MSS) for secure and simultaneous distributions of keys in a layered network. We present protocols for both quantum and semi-quantum key distribution and discuss their robustness against various eavesdropping strategies. We provide a procedure to identify the requisite resource states to generalize these protocols for arbitrary layered networks. Finally, we study the interrelation between the local dimensionalities of states and achievable key rates in a given layer. These proposals are realizable with current technology, thanks to the employment of MSS and many advances in the generation, manipulation, and measurement of higher-dimensional orbital angular momentum states of light.

Analysis and Optimization of STAR-RIS-Assisted Proactive Eavesdropping With Statistical CSI

In wireless surveillance, the monitor (E) should be far away from the suspicious system to maintain concealment, leading to very poor eavesdropping performance. To tackle this challenge, we propose in this paper a novel simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS)-assisted proactive eavesdropping strategy. Specifically, a STAR-RIS is deployed between E and the suspicious system to implement reflection (R) and transmission (T) for the suspicious signal of the suspicious transmitter and the jamming signal of E, to concurrently vary the channel power gains of the suspicious transmission link and the legitimate eavesdropping link and then facilitate E's eavesdropping. Assuming that E can only access the global statistical channel state information, we aim to maximize E's average (ergodic) eavesdropping rate, by jointly optimizing the energy splitting ratio of the STAR-RIS and E's jamming power. With rigorous analysis, we reveal that only two cases should be considered to achieve the optimal eavesdropping rate: i) the STAR-RIS works in T&R mode, and E does not conduct jamming; ii) the STAR-RIS only operates in T mode, and E interferes with the suspicious destination. In both cases, the optimal energy splitting ratio or jamming power is derived in (semi) closed form. Also, the eavesdropping energy (cost) efficiency is analyzed. Since our proposed strategy is adaptive, it can achieve significant eavesdropping performance gain compared to competitive benchmarks, as verified by numerical results.

Circulant Shift-Based Beamforming for Secure Communication With Low-Resolution Phased Arrays

Millimeter wave (mmWave) technology can achieve high-speed communication due to the large available spectrum. Furthermore, the use of directional beams in mmWave system provides a natural defense against physical layer security attacks. In practice, however, the beams are imperfect due to mmWave hardware limitations such as the low-resolution of the phase shifters. These imperfections in the beam pattern introduce an energy leakage that can be exploited by an eavesdropper. To defend against such eavesdropping attacks, we propose a directional modulation-based defense technique where the transmitter applies random circulant shifts of a beamformer. We show that the use of random circulant shifts together with appropriate phase adjustment induces artificial phase noise (APN) in the directions different from that of the target receiver. Our method corrupts the phase at the eavesdropper without affecting the communication link of the target receiver. We also experimentally verify the APN induced due to circulant shifts, using channel measurements from a 2-bit mmWave phased array testbed. Using simulations, we study the performance of the proposed defense technique against a greedy eavesdropping strategy in a vehicle-to-infrastructure scenario. The proposed technique achieves better defense than the antenna subset modulation, without compromising on the communication link with the target receiver.

Quantum Key Distribution Using a Single-Photon Added–Subtracted Squeezed Coherent State

We investigate the security of continuous-variable BB84 quantum key distribution protocol using a single-photon added and then subtracted squeezed coherent state (SPASSCS). We find that the SPASSCS is a non-Gaussian and nonclassical state; its non-Gaussianity and nonclassicality are exhibited through the Wigner function. We show that the proposed state is generally robust against the eavesdropping strategies, such as intercept-resend attack and superior channel attack. Further, a comparative study proves the strong efficiency of the proposed state over the coherent state, squeezed coherent state and photon-added then subtracted coherent state. In our analysis, we employ bit error rate, mutual information, and secure key gain.

Eavesdropping Strategies for Remote State Estimation Under Communication Constraints

This paper studies the confidentiality issue of wireless sensor networks under communication constraints from the perspective of an eavesdropper. The considered communication constraints include both medium access constraint and bandwidth limitation. Specifically, the former results in only one sink node gaining access to the shared network at each time step, while the latter requires data to be quantized by a probabilistic quantizer before being transmitted. The task of the eavesdropper is to develop eavesdropping strategies for the constrained network to infer the state of the system as accurately as possible. Since the data is generally unreadable to unauthorized third parties in terms of secure transmission, an eavesdropper with limited power must decide which sink nodes’ data needs to be decrypted. By analyzing the impact of different decryption strategies on the eavesdropping performance, a deciphering scheduling is proposed, which minimizes the expected estimation error without exceeding the energy budget. Besides, a recursive reset algorithm is put forward based on the properties of the probabilistic quantizer, which reflects that an eavesdropper can infer whether its own estimate is accurate enough from the decoded data. Moreover, a sufficient condition is established in which the eavesdropping performance is improved under the proposed algorithm. A numerical example is provided to demonstrate the validity of the developed approaches.

Explicit attacks on the Bennett-Brassard 1984 protocol with partially distinguishable photons

Distinguishability of photons in non-operational degrees of freedom compromises unconditional security of quantum key distribution since an eavesdropper can improve attack strategies by exploiting this distinguishability. However, the optimal eavesdropping strategies in the presence of light source side channels are not known. Here we provide several explicit attack strategies on the BB84 protocol with partially distinguishable photons. In particular, we consider the phase-covariant cloning attack, which is optimal in the absence of side channels, and show that there are even better strategies in the presence of side channels. The improved strategies exploit a measurement of the side channel state followed by an attack on the signal photon. Our results explicitly demonstrate reduction of the critical error rate, and set an upper bound on the practical secret key rate.

Security of quantum key distribution with detection-efficiency mismatch in the multiphoton case

Detection-efficiency mismatch is a common problem in practical quantum key distribution (QKD) systems. Current security proofs of QKD with detection-efficiency mismatch rely either on the assumption of the single-photon light source on the sender side or on the assumption of the single-photon input of the receiver side. These assumptions impose restrictions on the class of possible eavesdropping strategies. Here we present a rigorous security proof without these assumptions and, thus, solve this important problem and prove the security of QKD with detection-efficiency mismatch against general attacks (in the asymptotic regime). In particular, we adapt the decoy state method to the case of detection-efficiency mismatch.

Proactive Eavesdropping via Jamming in UAV-Enabled Relaying Systems With Statistical CSI

We investigate proactive eavesdropping with one half-duplex legitimate monitor (E) in unmanned aerial vehicle (UAV)-enabled suspicious relaying systems, which consist of a suspicious transmitter (ST), a suspicious UAV-based relay (SU) and a suspicious destination (SD). Under this setup, we propose two jamming-assisted eavesdropping strategies, namely, &#x201C;Eavesdrop-Then-Jam&#x201D; (ETJ) and &#x201C;Jam-Then-Eavesdrop&#x201D; (JTE), to maximize the eavesdropping throughput of E. Specifically, for ETJ, E first eavesdrops the suspicious signal of the ST in the ST-SU phase and then jams the SD in the SU-SD phase; for JTE, E first jams the SU in the ST-SU phase and then eavesdrops the suspicious signal of the SU in the SU-SD phase. <i>However, in both strategies, as the jamming power of E (independent variable) changes, the SU can also adaptively adjust its deployment (dependent variable) to maximize the benefit of the suspicious system</i>. Facing this challenge, we can only employ the undesirable exhaustive search over both the independent and dependent variables to achieve the optimal solution. To decrease the complexity, we further derive a tight approximation of the Lambert function and then develop easy-to-implement algorithms to find the sub-optimal solutions. Numerical results demonstrate the effectiveness of our proposed strategies compared to conventional passive eavesdropping.

The attack strategy for a quantum key distribution protocol based on Bell’s theorem

A new eavesdropping strategy is proposed for the Quantum Key Distribution (QKD) protocol. This scheme represents a new kind of intercept/resend strategy based on Bell’s theorem. Quantum key distribution (QKD) provides the foremost reliable form of secure key exchange, using only the input-output statistics of the devices to realize information-theoretic security. In this paper, we present an improved QKD protocol that can simultaneously distribute the quantum secret key. We are already using the QKD protocol with simulated results matched completely with the theoretical concepts.

Quantum control attack: Towards joint estimation of protocol and hardware loopholes

In this paper we present the quantum control attack on quantum key distribution systems. The cornerstone of the attack is that Eve can use unitary (polar) decomposition of her positive-operator valued measure elements, which allows her to realize the feed-forward operation (quantum control), change the states in the channel after her measurement and impose them to Bob. Below we consider the general eavesdropping strategy and the conditions those should be satisfied to provide the attack successfully. Moreover we consider several types of the attack, each of them is based on a different type of discrimination. We also provide the example on two non-orthogonal states and discuss different strategies in this case.

Generalized Discrimination Between Symmetric Coherent States for Eavesdropping in Quantum Cryptography

Symmetric coherent states are of interest in quantum cryptography, since for such states there is an upper bound for unambiguous state discrimination (USD) probability, which is used to resist USD attack. But it is not completely clear what an eavesdropper can do for shorter channel length, when USD attack in not available. We consider the task of generalized discrimination between symmetric coherent states and construct an operation which enlarges the information content of the states with fixed failure probability. We apply this transformation to develop a zero-error eavesdropping strategy for quantum cryptography on symmetric coherent states.

Jamming-Assisted Legitimate Eavesdropping and Secure Communication in Multicarrier Interference Networks

This article investigates legitimate eavesdropping and secure communication in a multicarrier interference network, where a suspicious link coexists with an unsuspicious link, in the presence of a full-duplex monitor. It is assumed that the unsuspicious users (UUs) are under illegal eavesdropping threat from the suspicious users (SUs), and the monitor can send jamming signals to interfere with the SUs. The UUs are required to cooperate with the monitor for reducing the secrecy outage probability of the UUs to be lower than that without the monitor’s jamming. Under this secrecy outage constraint along with the transmit power constraints, the problem for maximizing the successful eavesdropping probability of the monitor by jointly allocating the transmit powers of the monitor and the UUs is investigated. The problem is solved with the Lagrange duality method by proving the time-sharing property holds, where two algorithms are proposed for obtaining the dual function based on the block coordinate descent method and the successive convex approximation method. Simulation results verify that the proposed algorithms are superior to the noncooperative strategy and the passive eavesdropping strategy, and achieve high successful eavesdropping probability and low secrecy outage probability simultaneously.

Continuous variable B92 quantum key distribution protocol using single photon added and subtracted coherent states

In this paper, a continuous variable B92 quantum key distribution (QKD) protocol is proposed using single photon added and subtracted coherent states, which are prepared by adding and subsequently subtracting a single photon on a coherent state. It is established that in contrast to the traditional discrete variable B92 protocol, this protocol for QKD is intrinsically robust against the unambiguous state discrimination attack, which circumvents the requirement for any uninformative states or entanglement used in corresponding discrete variable case as a remedy for this attack. Further, it is shown that the proposed protocol is intrinsically robust against the eavesdropping strategies exploiting classical communication during basis reconciliation, such as beam splitter attack. Security against some individual attacks, key rate, and bit-error rate estimation for the proposed scheme are also provided. Specifically, the proposed scheme ensures very small bit-error rate due to properties of the states used. Thus, the proposed scheme is shown to be preferable over the corresponding discrete variable B92 protocol as well as some similar continuous variable quantum key distribution schemes.

Proactive Eavesdropping in Two-Way Amplify-and-Forward Relay Networks

This article considers a proactive eavesdropping scenario, where two suspicious nodes exchange their information via one suspicious relay in two phases, the process of which is under the supervision of one legitimate monitor. Specifically, these two suspicious nodes broadcast their suspicious data in phase 1 and the relay forwards the amplified version of its received signal in phase 2, according to which two proactive eavesdropping strategies, i.e., “passive eavesdropping first” and “jamming first,” are designed. Using the former strategy, the monitor proceeds eavesdropping with a minimum-mean-squar-error (MMSE) receiver in phase 1 and implements eavesdropping or simultaneous assisting and jamming in phase 2. Using the latter strategy, the monitor implements jamming in phase 1 and performs eavesdropping in phase 2. For these strategies, we provide the detailed analysis and formulate the corresponding optimization problems of sum eavesdropping rate maximization subject to finite transmit power of the monitor, each of which is then solved by carefully designing the power allocation scheme or the assisting/jamming beamformer at the legitimate monitor. In addition, for the “passive eavesdropping first” strategy, we also consider a more advanced MMSE with a successive interference cancellation (SIC) receiver and concurrently exploit the time-sharing (TS) technique to further improve the eavesdropping rate. Finally, simulation results indicate that the “passive eavesdropping first” strategy is more preferable compared to the “jamming first” strategy, and the SIC and TS are preferable for promoting the more effective eavesdropping.

High-dimensional quantum key distribution using polarization-phase encoding: security analysis

In this work, we introduce a high-dimensional polarization-phase (PoP)-based quantum key distribution protocol, briefly named PoP[Formula: see text], where [Formula: see text] is the dimension of a hybrid quantum state including polarization and phase degrees of freedom of the same photon, and [Formula: see text] is the number of mutually unbiased bases. We present a detailed description of the PoP[Formula: see text] protocol as a special case, and evaluate its security against various individual and coherent eavesdropping strategies, and in each case, we compare it with the BB84 and the two-dimensional (TD)-PoP protocols. In all the strategies, the error threshold and the effective transmission rate of the PoP[Formula: see text] protocol are far greater than the other two protocols. Unlike most high-dimensional protocols, the simplicity of producing and detecting the qudits and the use of conventional components (such as traditional single-photon sources and quantum channels) are among the features of the PoP[Formula: see text] protocol.

Legitimate Eavesdropping in Two-Way AF Relay Networks

This letter considers a legitimate surveillance scenario, where two suspicious nodes intend to exchange their information via one suspicious amplify-and-forward relay in two phases, the process of which is under the supervision of one legitimate monitor. To achieve the effective surveillance, one novel eavesdropping strategy is designed, in which the monitor proceeds passive eavesdropping in phase 1 and then implements passive eavesdropping or simultaneous assisting and jamming in general in phase 2. Under this setup, the monitor mainly aims to design the optimal structure of the transmit signal for each specific strategy in phase 2 and then optimize the corresponding beamformers and power allocation, in order to maximize the obtained sum eavesdropping rate subject to its power constraints. Simulation results verify that, compared to the conventional schemes, the proposed adaptive eavesdropping strategy achieves significant performance gains.

Privacy-Preserving Consensus over a Distributed Network against Eavesdropping Attacks

Motivated by the increasing risk of data leaks in distributed networks, we consider the privacy-preserving problem in a consensus network in the presence of an eavesdropper who is able to intercept the data transmitted on the network. First, we introduce a consensus protocol with privacy-preserving function, and analyze its convergence and its privacy-preserving effect. Second, we propose a criterion to measure the degree of network privacy leaks in the existence of the eavesdropper. Particularly, we consider the networks with ring topology and small-world topology, where we find a suboptimal eavesdropping strategy that maximizes the probability of privacy leaks. Finally, we verify all the derived results by numerical examples.