Abstract The metrology of the QKD devices and systems grows increasingly important in recent years not only because of the needs for conformance and performance testing in the standardization, but more importantly, imperfect implementation of the devices and systems or deviations from the theoretical models, which could be exploited by eavesdropper, should be carefully characterised to avoid the so-called side channel attack. In this paper, we review the recent advances in many aspects of the QKD metrology in both fibre based QKD and free space QKD systems, including a cutting edge metrology facility development and application, traceable calibration methods, and practical device characterising technologies, all of which have been contributed by the metrology communities and relative institutions.
Abstract The metrology of the QKD devices and systems grows increasingly important in recent years not only because of the needs for conformance and performance testing in the standardization, but more importantly, imperfect implementation of the devices and systems or deviations from the theoretical models, which could be exploited by eavesdropper, should be carefully characterised to avoid the so-called side channel attack. In this paper, we review the recent advances in many aspects of the QKD metrology in both fibre based QKD and free space QKD systems, including a cutting edge metrology facility development and application, traceable calibration methods, and practical device characterising technologies, all of which have been contributed by the metrology communities and relative institutions.
Quantum Key Distribution, a fundamental component of quantum secure communication that exploits quantum states and resources for communication protocols, can future-proof the security of digital communications, when if advanced quantum computing systems and mathematical advances render current algorithmic cryptography insecure. A QKD system relies on the integration of quantum physical devices, as quantum sources, quantum channels and quantum detectors, in order to generate a true random (unconditionally secure) cryptographic key between two remote parties connected through a quantum channel. The gap between QKD implemented with ideal and real devices can be exploited to attack real systems, unless appropriate countermeasures are implemented. Characterization of real devices and countermeasure is necessary to guarantee security. Free-space QKD systems can provide secure communication to remote parties of the globe, while QKD systems based on entanglement are intrinsically less vulnerable to attack. Metrology to characterize the optical components of these systems is required. Actually, the “Optical metrology for quantum-enhanced secure telecommunication” Project (MIQC2) is steering the metrological effort for Quantum Cryptography in the European region in order to accelerate the development and commercial uptake of Quantum Key Distribution (QKD) technologies. Aim of the project is the development of traceable measurement techniques, apparatus, and protocols that will underpin the characterisation and validation of the performance and quantum-safe security of such systems, essential steps towards standardization and certification of practical implementations of quantum-based technologies.
In theory, quantum key distribution (QKD) provides information-theoretic security based on the laws of physics. Owing to the imperfections of real-life implementations, however, there is a big gap between the theory and practice of QKD, which has been recently exploited by several quantum hacking activities. To fill this gap, a novel approach, called measurement-device-independent QKD (mdiQKD), has been proposed. It can remove all side-channels from the measurement unit, arguably the most vulnerable part in QKD systems, thus offering a clear avenue toward secure QKD realisations. Here, we review the latest developments in the framework of mdiQKD, together with its assumptions, strengths, and weaknesses.
Quantum Key Distribution (QKD) supports the negotiation and sharing of private keys with unconditional security between authorized parties. Over the years, theoretical advances and experimental demonstrations have successfully transitioned QKD from laboratory research to commercial applications. As QKD expands its reach globally, it encounters challenges such as performance limitations, cost, and practical security concerns. Nonetheless, innovations in satellite-based QKD and the development of new protocols are paving the way towards a worldwide network. In this review, we provide an overview of QKD implementations, with a focus on protocols, devices, and quantum channels. We discuss the challenges of practical QKD and explore long-haul QKD. Additionally, we highlight the future research directions that are expected to significantly advance the realization of a global QKD network.
Quantum Key Distribution (QKD) promises information-theoretic security based on the fundamental laws of quantum mechanics. However, practical implementations deviate from idealized models and are therefore susceptible to side-channel attacks that exploit physical imperfections rather than theoretical vulnerabilities. Over the past two decades, a wide range of attacks have been demonstrated against QKD systems, including those targeting detectors, sources, timing information, power consumption, and electromagnetic emissions. This paper addresses a selection of a few side-channel attacks reported in the literature, classifying them according to their underlying physical mechanisms and attack strategies. We analyze their impact on the security of different QKD protocols and platforms, and highlight how experimental demonstrations have shaped the community's understanding of implementation security. In addition, we present and evaluate mitigation techniques proposed to date, such as device-independent and measurement-device-independent QKD, hardware countermeasures, monitoring strategies, and so on. We also identify open challenges and promising directions for enhancing the robustness of future quantum communication systems.
Quantum Key Distribution (QKD) represents a revolutionary mechanism ensuring secure communication amidst the quantum computing era. With the evolving threat landscape due to quantum computing advancements, there’s an urgent need for a comprehensive review and assessment of existing QKD protocols and implementations. This paper systematically explores the QKD landscape, focusing on protocols, security models, practical implementations, and recent progress. We commence by elucidating the foundational principles of QKD and its pivotal role in establishing verifiably secure communication channels. Based on their underlying principles, we then categorize and scrutinize various QKD protocols, like BB84, BBM92, CV-QKD, etc. We delve into the security models utilized in QKD protocols, evaluating their strengths and limitations. Additionally, we evaluate practical QKD system implementations encompassing both fibre-based and free-space setups. We shed light on crucial technological challenges, advancements, and recent developments in quantum repeaters, memories, and network architectures aiming to enhance the reach and scalability of QKD systems. This systematic review provides insights into the current state of QKD technology, identifies research gaps, and discusses potential pathways for future progress. Our analysis is a vital resource for researchers and practitioners who are engaged in quantum cryptography and secure communication protocols.
Quantum Key Distribution (QKD) constitutes one of the most profound practical applications of quantum mechanics, enabling two parties to exchange cryptographic keys whose security is guaranteed by the fundamental laws of physics rather than the assumed computational hardness of mathematical problems. As quantum computing capabilities continue to advance, classical public-key infrastructure faces an existential threat, rendering QKD a critical component of post-quantum secure communication architectures. This paper presents a comprehensive survey of QKD spanning foundational protocols, rigorous security proofs, hardware implementation challenges, deployment experiences across metropolitan fiber networks, and recent satellite-based experiments. We analyze the BB84, E91, B92, SARG04, continuous-variable, measurement-device-independent (MDI-QKD), and twin-field (TF-QKD) protocols in depth, examining their security assumptions, achievable key rates, and practical limitations. Particular attention is given to side-channel vulnerabilities in realistic implementations, decoy-state methods for mitigating photon-number-splitting attacks, and finite-key security analysis. We review key performance benchmarks from commercial systems and discuss integration with classical network infrastructure. The paper concludes by identifying open challenges in quantum repeater development, satellite QKD scalability, and standardization efforts essential for large-scale deployment.