Submarine cable systems, serving as the critical backbone of global communications, face evolving resilience threats. This work proposes a novel sensing attack that utilizes ultra-narrow-linewidth lasers to surveil these infrastructures. First, the Narrowband Jamming Attack (NJA) is introduced as an evolution of conventional physical-layer jamming. NJA is divided into three categories according to the spectral position, and the non-overlapping class represents the proposed sensing attack. Its operational principles and the key parameters determining its efficacy are analyzed, along with its deployment strategy in submarine cable systems. Finally, the sensing capability is validated via OptiSystem simulations. Results demonstrate successful localization of vibrations within the 50–200 Hz range on a 1 km fiber, achieving a spatial resolution of 1 m, and confirm the influence of vibration parameters on sensing performance. This work reveals that the proposed sensing attack has the potential to covertly monitor environmental data, thereby posing a threat to information security in submarine cable systems.
Submarine cable systems, serving as the critical backbone of global communications, face evolving resilience threats. This work proposes a novel sensing attack that utilizes ultra-narrow-linewidth lasers to surveil these infrastructures. First, the Narrowband Jamming Attack (NJA) is introduced as an evolution of conventional physical-layer jamming. NJA is divided into three categories according to the spectral position, and the non-overlapping class represents the proposed sensing attack. Its operational principles and the key parameters determining its efficacy are analyzed, along with its deployment strategy in submarine cable systems. Finally, the sensing capability is validated via OptiSystem simulations. Results demonstrate successful localization of vibrations within the 50–200 Hz range on a 1 km fiber, achieving a spatial resolution of 1 m, and confirm the influence of vibration parameters on sensing performance. This work reveals that the proposed sensing attack has the potential to covertly monitor environmental data, thereby posing a threat to information security in submarine cable systems.
Initially considered secure against interception, fiber-optic networks were subsequently found susceptible to covert tapping, although such attacks require different coupling mechanisms and components than those used for twisted pair and coaxial cables. Fiber-optic networks carry the majority of data and voice traffic worldwide, including backhaul and fronthaul traffic in 4G and 5G radio networks, connections between data centers, and submarine cable systems. Consequently, physical access to fibers for interception has attracted the attention of intelligence agencies and industrial spies. This vulnerability is facilitated by the fact that single-mode optical fibers (SMFs) used in telecommunication networks have evolved relatively little over the last 40 years. Fibers of substantially different designs—anti-resonant hollow core fibers (HCF) and multi-core fibers (MCF)—made their commercial debut around 2023, and their susceptibility to tapping may differ substantially from that of conventional SMFs. New promising fiber monitoring techniques based on polarization measurements have also been demonstrated recently. While established tapping techniques remain feasible for conventional fibers, new fiber designs and monitoring technologies can make covert interception difficult. This review examines physical fiber tapping techniques and their practical feasibility, with particular emphasis on optical power constraints, introduced loss, detectability, and implementation limitations. It also reviews prevention and monitoring approaches, including optical time-domain reflectometry, received-power monitoring, and state-of-polarization (SOP) monitoring, and provides a prospective engineering assessment of the susceptibility of MCFs and HCFs to physical tapping.
In this paper, we investigate how data transmissions may be affected by various types of optical interference introduced into the fiber on purpose, via a clip-on coupler. The research proved that transmissions may be jammed completely using inexpensive equipment readily available on the market, provided that the attacker has physical access to the fiber optic cable. The most dangerous attacks rely on a typical, slowly modulated communication laser with a rectangular waveform. This study urges further research aimed at counteracting such attacks.
Continuous-Variable Quantum Key Distribution (CV-QKD) offers practical advantages for secure communication, but laser linewidth-induced phase noise remains a critical performance limitation. This work presents a comprehensive simulation-based analysis quantifying the impact of laser linewidth on secret key rate (SKR) in Gaussian-modulated coherent-state CV-QKD systems. We develop a detailed noise model incorporating detector electronics, Raman scattering, phase recovery, ADC quantization, and laser relative intensity noise. Through systematic parameter sweeps spanning linewidths from 10 Hz to 250 kHz, modulation variances from 1 to 20 SNU, and fiber distances up to 100 km, we identify three distinct operational regimes and optimization strategies for both transmitted local oscillator (TLO) and local–local oscillator (LLO) configurations under homodyne and heterodyne detection. Results show that metropolitan-scale links (50 km) require linewidths below 5 kHz to maintain secure operation, with performance decreasing beyond 25 kHz. We demonstrate that modulation variance must be jointly optimized with laser quality, with optimal values decreasing from 3–4 SNU at narrow linewidths to 2–2.5 SNU at moderate linewidths. The analysis reveals asymmetric sensitivity in LLO systems where local oscillator linewidth degrades performance more strongly than signal laser linewidth. These quantitative findings provide practical design guidelines for achieving secure CV-QKD operation over metropolitan distances with realistic hardware constraints, supporting deployment of defense-grade quantum communication networks.
As the backbone of global communication infrastructure, optical fibers carry vast amounts of sensitive data, making them prime targets for eavesdropping attacks that can compromise data confidentiality and national security. However, optical fibers are highly vulnerable to eavesdropping attacks-such as fiber bending or evanescent coupling-which can eavesdrop on data without interrupting the service. Accurate detection of eavesdropping remains a critical challenge, particularly under complex environmental disturbances. Environmental factors such as fluctuation and disturbances can induce signal distortions and polarization variations that mask or mimic eavesdropping characteristics, thereby posing a significant challenge to the training and generalization of machine learning-based classifiers. In this Letter, we propose a sensing framework based on a hybrid gated recurrent unit-convolutional neural network model that jointly analyzes polarization parameters and error vector magnitude. The proposed method enables accurate and robust eavesdropping detection and temporal localization under complex physical environments. Experiments conducted across seven practical scenarios demonstrate that the proposed scheme achieves a detection accuracy of 97.2%. Furthermore, we developed real-time and offline optical fiber monitoring platforms integrating mainstream detection techniques to facilitate comprehensive evaluation and deployment.
The wavelength attack utilizes the dependence of beam splitters (BSs) on wavelength to cause legitimate users Alice and Bob to underestimate their excess noise so that Eve can steal more secret keys without being detected. Recently, the wavelength attack on Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) has been researched in both fiber and atmospheric channels. However, the wavelength attack may also pose a threat to the case of ocean turbulent channels, which are vital for the secure communication of both ocean sensor networks and submarines. In this work, we propose two wavelength attack schemes on underwater discrete modulated (DM) CV-QKD protocol, which is effective for the case with and without local oscillator (LO) intensity monitor, respectively. In terms of the transmittance properties of the fused biconical taper (FBT) BS, two sets of wavelengths are determined for Eve's pulse manipulation, which are all located in the so-called blue-green band. The derived successful criterion shows that both attack schemes can control the estimated excess noise of Alice and Bob close to zero by selecting the corresponding condition parameters based on channel transmittance. Additionally, our numerical analysis shows that Eve can steal more bits when the wavelength attack controls the value of the estimated excess noise closer to zero.
Ensuring secure optical wireless communication in underwater environments is a critical challenge, but still largely unexplored. In this work, we propose a novel physical-layer jamming scheme based on multi-mirror reflection and cooperative interference. Specifically, we consider concave mirrors with low curvature paired with an optical concentrator as integrated at both the transmitter and the legitimate receiver. his architecture collects the incident jamming signal over a wide acceptance angle, focuses it onto the mirror surface, and re-radiates it over an enlarged apparent source area, yielding a significant intensity gain on the jamming path toward the eavesdropper. The resulting jamming reflections significantly impair the capability of a potential passive eavesdropper to intercept the communication. On the other hand, the integrity and quality of the legitimate link is guaranteed. Such a security framework is presented for the typical optical signaling based on intensity modulation and direct detection, and its passive, zero-overhead architecture requires no knowledge of the eavesdropper's position or channel, making it particularly suited to dynamic underwater deployments. The effectiveness of the proposed strategy is validated through simulations, including a detailed model of optical propagation in different channel scenarios and water types affected by turbulenceinduced fading. At the eavesdropper side, successive interference cancellation based detection is assumed, since it results as the most favorable strategy for the eavesdropper and yielding a conservative lower bound on the system secrecy performance. Numerical results confirm that even when the eavesdropper has perfect knowledge of the illegitimate link, the proposed scheme achieves robust physical-layer security across a wide range of underwater conditions, preserving the legitimate link reliability.