The development of fi ber-optic communication and data transmission systems gives rise to a number of new challenges, among which information protection against unauthorized access is of particular relevance. In response to this need, quantum cryptography has emerged – optical cryptographic systems with quantum key distribution. Such systems protect communication channels by encrypting data with a one-time secret key. The theoretical foundation guaranteeing secure key transmission relies on the Heisenberg uncertainty principle and the no-cloning theorem for quantum states of elementary particles. However, real-world quantum cryptography systems exhibit vulnerabilities stemming from imperfections in their components. Single photon detectors and single photon sources are critical elements of quantum key distribution systems. This work analyses the main types of attacks on quantum cryptography equipment and identifi es the key parameters of single photon sources and single photon detectors. Knowledge of their actual values can be crucial for proving a system’s resilience against attacks. Additionally, the paper describes the equipment and methods used to study single-photon sources. The study also describes the method and results of investigating the quantum effi ciency and false trigger probabilities of gated single-photon detectors with fi ber input. The described measurement methods are harmonized with the recommendations of the European Telecommunications Standards Institute. Together, the described measurement techniques and setups enable the assessment of single photon source and detector parameters during expert evaluation of quantum cryptography system vulnerabilities. The paper concludes with a call for the establishment of a reference database to support metrological assurance of key parameters for single photon sources and receivers, in order to advance quantum cryptography systems
The development of fi ber-optic communication and data transmission systems gives rise to a number of new challenges, among which information protection against unauthorized access is of particular relevance. In response to this need, quantum cryptography has emerged – optical cryptographic systems with quantum key distribution. Such systems protect communication channels by encrypting data with a one-time secret key. The theoretical foundation guaranteeing secure key transmission relies on the Heisenberg uncertainty principle and the no-cloning theorem for quantum states of elementary particles. However, real-world quantum cryptography systems exhibit vulnerabilities stemming from imperfections in their components. Single photon detectors and single photon sources are critical elements of quantum key distribution systems. This work analyses the main types of attacks on quantum cryptography equipment and identifi es the key parameters of single photon sources and single photon detectors. Knowledge of their actual values can be crucial for proving a system’s resilience against attacks. Additionally, the paper describes the equipment and methods used to study single-photon sources. The study also describes the method and results of investigating the quantum effi ciency and false trigger probabilities of gated single-photon detectors with fi ber input. The described measurement methods are harmonized with the recommendations of the European Telecommunications Standards Institute. Together, the described measurement techniques and setups enable the assessment of single photon source and detector parameters during expert evaluation of quantum cryptography system vulnerabilities. The paper concludes with a call for the establishment of a reference database to support metrological assurance of key parameters for single photon sources and receivers, in order to advance quantum cryptography systems
The last two decades have witnessed an exciting advanced research field that stems from non-classical atomic theory, the quantum mechanics. This research promises an interesting applicability in computation, known as quantum computation, and also in secure data communications, known as quantum cryptography. Quantum cryptography capitalizes on the inherent random polarization state of single photons, which are associated with binary logic values. Because the polarization state of a photon is not reproducible by an eavesdropper between the source and the destination, polarized photons are used with an intelligent algorithm to disseminate the cryptographic key with high security from the source to the destination, a process known as quantum key distribution. However, although the polarization state of a photon remains intact in free-space propagation, it does not remain so in dielectric medium and thus quantum cryptography is not problem-free. In this paper we review quantum cryptography and we identify the various steps in the quantum key identification process. We then analyze and discuss issues related to quantum key distribution that rise in pragmatic fiber-optic transmission and in communication network topologies. In addition, we identify a major weakness of the method that is prone to attacking and which incapacitates quantum cryptography in fiber communications.
Quantum cryptography or quantum key distribution (QKD) applies fundamental laws of quantum physics to guarantee secure communication. The security of quantum cryptography was proven in the last decade. Many security analyses are based on the assumption that QKD system components are idealized. In practice, inevitable device imperfections may compromise security unless these imperfections are well investigated.\n\nA highly attenuated laser pulse which gives a weak coherent state is widely used in QKD experiments. A weak coherent state has multi-photon components, which opens up a security loophole to the sophisticated eavesdropper. With a small adjustment of the hardware, we will prove that the decoy state method can close this loophole and substantially improve the QKD performance. We also propose a few practical decoy state protocols, study statistical fluctuations and perform experimental demonstrations. Moreover, we will apply the methods from entanglement distillation protocols based on two-way classical communication to improve the decoy state QKD performance. Furthermore, we study the decoy state methods for other single photon sources, such as triggering parametric down-conversion (PDC) source. Note that our work, decoy state protocol, has attracted a lot of scientific and media interest. The decoy state QKD becomes a standard technique for prepare-and-measure QKD schemes.\n\nAside from single-photon-based QKD schemes, there is another type of scheme based on entangled photon sources. A PDC source is commonly used as an entangled photon source. We propose a model and post-processing scheme for the entanglement-based QKD with a PDC source. Although the model is proposed to study the entanglement-based QKD, we emphasize that our generic model may also be useful for other non-QKD experiments involving a PDC source. By simulating a real PDC experiment, we show that the entanglement-based QKD can achieve longer maximal secure distance than the single-photon-based QKD schemes.\n\nWe propose a time-shift attack that exploits the efficiency mismatch of two single photon detectors in a QKD system. This eavesdropping strategy can be realized by current technology. We will also discuss counter measures against the attack and study the security of a QKD system with efficiency mismatch detectors.
The last two decades have witnessed an exciting advanced research field that stems from non-classical atomic theory, the quantum mechanics. This research promises an interesting applicability in computation known as quantum computation, and also in secure data communications, known as quantum cryptography Quantum cryptography capitalizes on the inherent random polarization state of single photons, which are associated with binary logic values. Because the polarization state of a photon is not reproducible by an eavesdropper between the source and the destination polarized photons are used with an intelligent algorithm to disseminate the cryptographic key with high security from he source to the destination, a process known as quantum key distribution. However, although the polarization state of a photon remains intact in free- space propagation, it does not remain so in dielectric medium and thus quantum cryptography is not problem- free. In this paper we review quantum cryptography and we identify the various steps in the quantum key identification process. We then analyze and discuss issues related to quantum key distribution that rise in pragmatic fiberoptic transmission and in communication network topologies. In addition, we identify a major weakness of the method that is prone to attacking and which incapacitates quantum cryptography in fiber communications.
In the last ten years, quantum computing has made substantial progress, presenting a strong challenge to traditional encryption methods that depend on solving discrete algorithmic problems. With the advent of the quantum era, conventional encryption methods are becoming more susceptible to attacks. This paper investigates possible attacks that exploit vulnerabilities in quantum cryptography, specifically investigating weaknesses in quantum key distribution (QKD) systems. The text thoroughly explores advanced attack strategies of photon number splitting highlight the existing vulnerabilities. The goal is to highlight the need for strong safeguards to protect against these threats, which requires continuous research and development to improve the robustness of quantum cryptography algorithms. The experimental investigation includes analyzing crucial parameters, including quantum channel length, loss, QKD protocol, quantum bit error rate (QBER), signal-to-noise ratio (SNR), as well as attack parameters such as probability of photon number splitting (PNS), eavesdropper distance, and detection efficiency. The evaluation includes performance indicators such as secure key rate, quantum bit error rate (QBER) vs distance, vulnerability to photon number splitting (PNS) attacks, and the influence on the pace of key generation.
The emergence of a digital communications infrastructure over recent decades has fuelled the parallel development of advanced cryptographic techniques, to secure the ever increasing quantities of digital infonnation. From its foundation, quantum key distribution has generated significant theoretical and experimental research interest since it offers what ./ is currently the only method of verifiably secure cryptographic key distribution. By using the Heisenberg Uncertainty Principle, quantum key distribution offers a technique by which authorised parties can detect the potential presence of an eavesdropping unauthorised party and take appropriate action. Previous demonstrations of quantum key distribution have typically concentrated on extending the maximum transmission distance over which communication may be performed at the expense of bit-rates. This thesis investigates a quantum key distribution system operating at a wavelength of 850 nm in standard telecommunications fibre using commercially available silicon single-photon avalanche diodes to achieve clock rates in excess of 1 GHz, with a corresponding increase in received bit-rates. The principles of currently implemented passive optical networks are then applied to the system to demonstrate multi-user quantum key distribution systems. In addition, the point-to-point (single-user) system is demonstrated at a clock-rate of 3.3 GHz using low timing jitter niobium nitride nanowire superconducting detectors to demonstrate the highest clock-rate transmission in standard telecommunications optical fibre and the highest channel loss to date. Finally, single-photon sources based on quantum dot microcavity resonators are also examined for use in quantum key distribution.
The last two decades have witnessed an exciting advanced research field that stems from non-classical atomic theory, quantum mechanics. This field promises an important applicability in secure data communications, known as quantum cryptography. Quantum cryptography takes advantage of the inherent random polarization state of single photons, which is not reproducible by a third party or an eavesdropper located between the source and the destination. Thus, when polarization states of photons are associated with binary logic an algorithm may intelligently developed according to which a cryptographic key is disseminated by the source terminal to the destination. This is a process known as quantum key distribution. However, as photons propagate in a non-linear medium such as fiber, their polarization state does not remain intact and thus the quantum key distribution and quantum cryptography becomes vulnerable to attacks. In this paper we consider the applicability of quantum cryptography in a pragmatic fiber-optic medium and in a popular communication network topology. We identify major weaknesses for each step of the quantum key distribution process, and also potential attacks to incapacitate quantum cryptography in fiber communications, so that better countermeasure strategies can be developed.