Abstract : Quantum Key Distribution (QKD) systems combine cryptographic primitives with quantum information theory to produce a theoretic unconditionally secure cryptographic key. However, real-world implementations of QKD systems are far from ideal and differ significantly from the theoretic model. Because of this, real-world QKD systems require additional practical considerations when implemented to achieve secure operations. In this thesis, a content analysis of the published literature is conducted to determine if established security and cryptographic standards and best practices are addressed in real world, practical QKD implementations. The research reveals that most published, real world QKD implementations do not take advantage of established security and cryptographic standards and best practices. Based upon an analysis of existing security and cryptographic standards and best practices, systems architecture methodology is used to make recommendations as to how these standards can and should be applied to establish a practical, secure, QKD system framework.
Abstract : Quantum Key Distribution (QKD) systems combine cryptographic primitives with quantum information theory to produce a theoretic unconditionally secure cryptographic key. However, real-world implementations of QKD systems are far from ideal and differ significantly from the theoretic model. Because of this, real-world QKD systems require additional practical considerations when implemented to achieve secure operations. In this thesis, a content analysis of the published literature is conducted to determine if established security and cryptographic standards and best practices are addressed in real world, practical QKD implementations. The research reveals that most published, real world QKD implementations do not take advantage of established security and cryptographic standards and best practices. Based upon an analysis of existing security and cryptographic standards and best practices, systems architecture methodology is used to make recommendations as to how these standards can and should be applied to establish a practical, secure, QKD system framework.
Abstract Quantum Key Distribution (QKD) systems combine cryptographic primitives with quantum information theory to produce a theoretic unconditionally secure cryptographic key. However, real‐world implementations of QKD systems are far from ideal and significantly differ from the theoretic models. Because of this real‐world QKD systems require additional practical considerations when implemented to achieve secure operations. In this paper, a content analysis of the published literature is conducted to determine if established security and cryptographic standards are addressed in real world, practical QKD implementations. The research reveals that a majority of real world QKD implementations examined do not take advantage of established security and cryptographic standards. Based upon an analysis of existing industry security and cryptographic standards and best practices, systems architecture guidelines are used to make recommendations for how these standards can and should be applied to establish a practical, secure, QKD system framework.
The rise of quantum computing poses a grave threat to current cryptographic methods. While Quantum Key Distribution (QKD) offers a potential solution, guaranteeing its security in real-world implementations remains challenging. This paper addresses the critical need for robust Quantum Encryption algorithms, emphasizing the importance of standardized evaluation criteria and it explores the limitations of existing evaluation methods, highlighting their shortcomings in comprehensively assessing security against both classical and quantum attacks. Furthermore, a comprehensive framework for evaluating and standardizing Quantum Encryption algorithms is proposed. This framework encompasses not only the algorithm itself but also the security of the generated key. By incorporating a broader range of attack scenarios, theoretical considerations, and key-specific criteria, this framework aims to ensure the confidentiality and integrity of communication in the quantum age.This research is believed to make a significant contribution to the development of secure and standardized Quantum Encryption algorithms. The goal is to safeguard critical information infrastructure against evolving threats. Existing works have placed a strong emphasis on standardizing QKD (Quantum Key Distribution). However, the evaluation of the effectiveness of quantum encryption algorithms lacks the same level of standardization. This gap serves as the motivation behind this work.
Quantum Key Distribution (QKD) offers information-theoretic security grounded in the laws of quantum mechanics rather than computational assumptions. While its theoretical foundations are robust, practical implementations necessarily deviate from the idealized models assumed in security analyses, opening the door to side-channel attacks and implementation loopholes. In particular, most research to date has focused on mitigating vulnerabilities in the measurement devices, leading to the development of Measurement-Device-Independent QKD (MDI-QKD) and Twin-Field QKD (TF-QKD), which effectively close all receiver-side loopholes. By contrast, the security of the source has remained less explored, despite being critical for the overall integrity of QKD systems. The goal of this thesis is to develop security proofs that explicitly account for realistic imperfections in QKD sources. Special emphasis is placed on three main aspects: correlations between emitted pulses that violate independence assumptions, imperfect phase randomization arising from practical modulation schemes, and leakage of internal settings through passive or active side channels. By formulating rigorous methods to analyze these imperfections, the work aims to provide a framework that enables practitioners to quantify and mitigate implementation risks systematically. Additionally, this thesis seeks to clarify under which conditions the commonly used decoy-state method remains secure, and to what extent source assumptions can be relaxed without compromising performance. This thesis aims to advance the understanding of how real-world deviations impact QKD security and to contribute to the development of protocols and devices. Ultimately, this work is motivated by the ambition to help bring QKD from a theoretically promising idea to a mature technology deployable with confidence in practical scenarios.
Information security becomes an inseparable part of our everyday life. An encryption \nmethod widely used today is public-key encryption. The security of this method is based on \na hard to solve mathematical problems against an adversary with limited computational \npower. Such an assumption could be broken as our understanding of the mathematics \nbeing improved or new computation tools being developed. One such tool that poses a \nthreat to the public key encryption is a quantum computer. As a result, a new encryption \nmethod with a new security assumption is required. \nQuantum key distribution is a point-to-point symmetric key distribution method with \nsecurity based on the law of physics. In theory, the key generated by QKD is informationtheoretic secured. However, in practice, physical devices could have flaws or possess some \nbehaviors deviated from the theoretical model. These imperfections could open security \nloopholes for an adversary to exploit, compromising the security. Thus the security verification and system characterization of practical implementation of QKD are necessary. \nThe necessity of this verification is further emphasized as several QKD systems are being \ncommercialized and used in several discrete communication links today. \nTo extend this new encryption system’s practical implementation on a wider network \nscale requires a set of standards or common practices for developers and service providers \nto follow. This set of rules is set to ensure the compatibility of different device models in \nthe network and ensure the security of each component in the system, which would affect \nthe security of the system as a whole. \nTo fulfill standardization and certification criteria, a record of best practice on security \nanalysis, system design, device characterization, and security verification of QKD implementation is required. The research projects throughout my Ph.D. study contribute toward \nthis practice. These studies also address some issues and provide possible solutions to the \ndevelopment of a standard for QKD. This thesis is a collection of six experimental studies \non performance evaluation and security verification of different components of practical \nquantum key distribution systems. \nThe first study is a comparison between the performance of the QKD system with \nquantum dot (QD) as a single-photon source and the performance of QKD with weakcoherent pulsed (WCP) source. The result shows that the QKD with QD could generate \nthe key at higher channel loss than WCP QKD using the same laser source. This result \nshows the potential of QKD with a single-photon source as a candidate for secret key \ndistribution over high channel loss, such as up-link satellite-based QKD. \nThe second study is a theoretical study on the method to characterize the QKD system \nagainst the Trojan-horse attack being considered as a standard for the QKD system. The \nresult shows a possible loophole of this method against a more powerful adversary than \nassumed in the previously proposed model. An improved version of characterization against \na more general form of Trojan-horse attack has been proposed. \nThe third experiment is on the information leakage from a free-space QKD receiver due \nto detector backflash, a photon produced by the detector upon detection. The result shows \nthat the backflash photons carry the information of the ’clicked’ detector that could be \ntransmitted back to the channel and discriminated by Eve. An experimental demonstration \nof this attack has been performed. Countermeasure both in theory and practical setup has \nbeen proposed. \nThe next experiment is on the effect of atmospheric turbulence on Eve’s spatial-mode \ndetection efficiency mismatch attack on the free-space QKD system. We show that, by \nusing a phase-only spatial light modulator (SLM) and hologram created by Zernike polynomials, atmospheric turbulence with various strength covered from sea level to upper \natmosphere can be experimentally emulated in the lab environment. We then use that \nsetup to show the limit of the distance that Eve’s attack is successful. The theoretical \nlimit of the attack distance also shown. \nIn the fifth study, we use the SLM and Zernike polynomial holograms to characterize a \nfree-space QKD system against spatial mode attack. The result shows that, with higherorder spatial modes and finer control of wavefront intensity distribution, Eve could bypass \nthe countermeasure proposed in our previous study. We proposed a more robust version \nof countermeasure against spatial mode attack. The new countermeasure is verified by the \nSLM setup. \nThe last study is on the fake-state attack on the transition edge sensor (TES). The \nresult shows that TES’s voltage response can be deterministically controlled by Eve using \nbright laser through the input channel. It also shows that the photon number result from \nTES can be controlled by Eve. An attack model exploiting this imperfection has been \nshown. \nIn addition to the contribution to the standardization of the QKD system, I hope that \nthe result of this thesis would emphasize the necessity of security verification of the QKD \nsystem and the verification of countermeasure and characterization method against more \ngeneral attack model. Although the unconditional security, promised in theory, could not \nyet be achieved, this loop of hacking and patching should provide us information and insight \non which security level could be claimed from the practical QKD devices implementing \ntoday.
Quantum key distribution (QKD) exploits the laws of quantum physics to generate shared secret cryptographic keys and can detect eavesdroppers during the key generation process. However, previous QKD research has focused more on theory than practice. QKD is the most mature application of the quantum information field, offering the means for two parties to generate secure cryptographic keying material. Employing the laws of quantum physics, QKD can detect eavesdroppers during the key generation process, in which unauthorized observation of quantum communication induces discernible errors. However, QKD is a nascent technology where real-world systems are constructed from nonideal components and deployed in uncertain operational environments, which can adversely impact system security and performance. In this article, we study the performance impact of QKD implementation nonidealities and practical engineering limitations, evaluating three system examples using a modularized simulation framework. We also explore the QKD security–performance trade space to gain additional understanding of critical design tradeoffs associated with interactions between physical components and system-level considerations such as hardware, software, and protocols. Such evaluations provide insight and inform designers, researchers, and users when selecting among competing solutions; decision makers can also use them to guide future investments and developmental efforts. Our research team focuses on bridging the gap between QKD theory and practice. Theoretical and experimental physicists are working to advance QKD technology, but few are strongly focused on evaluating and improving the implementation of realized systems. For a general introduction to QKD, see Chip Elliot’s “Quantum Cryptography.”