Abstract Quantum technology can enable secure communication for cryptography purposes using quantum key distribution. Quantum key distribution protocol establishes a secret key between two users with security guaranteed by the laws of quantum mechanics. To define the proper implementation of a quantum key distribution system using a particular cryptography protocol, it is crucial to critically and meticulously assess the device’s performance due to technological limitations in the components used. We perform simulations on the ANSYS Interconnect platform to study the practical implementation of these devices using distributed-phase-reference protocols: differential-phase-shift and coherent-one-way quantum key distribution. Further, we briefly describe and simulate some possible eavesdropping attempts, backflash attack, trojan-horse attack and detector-blinding attack exploiting the device imperfections. The ideal simulations of these hacking attempts show how partial or complete secret key can be exposed to an eavesdropper, which can be mitigated by the implementation of discussed countermeasures.
Abstract Quantum technology can enable secure communication for cryptography purposes using quantum key distribution. Quantum key distribution protocol establishes a secret key between two users with security guaranteed by the laws of quantum mechanics. To define the proper implementation of a quantum key distribution system using a particular cryptography protocol, it is crucial to critically and meticulously assess the device’s performance due to technological limitations in the components used. We perform simulations on the ANSYS Interconnect platform to study the practical implementation of these devices using distributed-phase-reference protocols: differential-phase-shift and coherent-one-way quantum key distribution. Further, we briefly describe and simulate some possible eavesdropping attempts, backflash attack, trojan-horse attack and detector-blinding attack exploiting the device imperfections. The ideal simulations of these hacking attempts show how partial or complete secret key can be exposed to an eavesdropper, which can be mitigated by the implementation of discussed countermeasures.
The huge discrepancies between actual devices and theoretical assumptions severely threaten the security of quantum key distribution. Recently, a general new framework called the reference technique has attracted wide attention in defending against the imperfect sources of quantum key distribution. Here, the state preparation flaws, the side channels of mode dependencies, the Trojan horse attacks, and the pulse classical correlations are studied by using the reference technique on the phase-matching protocol. Our simulation results highlight the importance of the actual secure parameters choice for transmitters, which is necessary to achieve secure communication. Increasing the single actual secure parameter will reduce the secure key rate. However, as long as the parameters are set properly, the secure key rate is still high. Considering the influences of multiple actual secure parameters will significantly reduce the secure key rate. These actual secure parameters must be considered when scientists calibrate transmitters. This work is an important step towards the practical and secure implementation of phase-matching protocol. In the future, it is essential to study the main parameters, find out their maximum and general values, classify the multiple parameters as the same parameter, and give countermeasures.
The peculiar properties of quantum mechanics enable possibilities not allowed by classical physics. In particular, two parties can generate a random, secret key at a distance, even though an eavesdropper can do anything permitted by the laws of physics. Measuring the quantum properties of the signals generating the key, would ultimately change them, and thus reveal the eavesdropper’s presence. This exchange of a random, secret key is known as quantum cryptography.\n\nQuantum cryptography can be, and has been proven unconditionally secure using perfect devices. However, when quantum cryptography is implemented, one must use components available with current technology. These are usually imperfect. Although the security of quantum cryptography has been proven for components with certain imperfections, the question remains: can quantum cryptography be implemented in a provable, unconditionally secure way, using components available with current technology? This thesis contains both a theoretical, and an experimental contribution to the answer of this question. On the experimental side, components used in, and complete quantum cryptography systems have been carefully examined for security loopholes. In particular, it turned out that two commercial quantum cryptography systems contained loopholes, which would allow an eavesdropper to capture the full secret key, without exposing her presence. Furthermore, this detector control attack could be implemented with current technology. The attack is applicable against a variety of quantum cryptography implementations and protocols.\n\nThe theoretical contribution consists of security proofs for quantum cryptography in a very general setting. Precisely, the security is proven with arbitrary individual imperfections in the source and detectors. These proofs should make it possible to use a wide array of imperfect devices in implementations of quantum cryptography.\n\nFinally, a secure detection scheme is proposed, immune to the detector control attack and compatible with those security proofs. Therefore, if this scheme is implemented correctly, it offers provable security.
Abstract Since the 80 s when it was first proposed, Quantum Key Distribution (QKD) elicited great interest in the field of cryptography as a unique procedure for key generation that could in principle guarantee unconditionally secure communication “by the laws of Physics”. In the last fifteen years commercial solutions have started appearing on the market, showing that practical implementations of the protocol were not only possible but also competitive in terms of security and achievable secret-key rate. In this work we describe a simulation of the historical QKD protocol E91 on the IBM Quantum platform, making use of the qubit formalism to represent the quantum states received by two communicating nodes. Having implemented also the post-processing steps for the error correction and the privacy amplification, this model can represent a simple stand-alone tool to study the performance not only of one-to-one communication but of more complex systems that rely on QKD for security, one above all QKD networks.
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.
Quantum Key Distribution (QKD) is an innovative technology which exploits the laws of quantum physics to generate and distribute shared secret key for use in cryptographic devices. Quantum Key Distribution offers the advantage of ‘unconditionally secure’ key generation with the unique ability to detect eavesdropping on the key distribution channel and shows promise for high-security applications such as those found in banking, government, and military environments. However, Quantum Key Distribution is a nascent technology where realized systems suffer from implementation non-idealities, which may significantly impact system performance and security. In this article, we discuss the modeling of a decoy state enabled Quantum Key Distribution system built to study the impact of these practical limitations. Specifically, we present a thorough background on the decoy state protocol, detailed discussion of the modeled decoy state enabled Quantum Key Distribution system, and evidence for component and sub-system verification, as well as, multiple examples of system-level validation. Additionally, we bring attention to practical considerations associated with implementing the decoy state protocol security condition gained from these research activities.
The coherent-one-way and the differential-phase-shift protocols ar e two of the most recent practical quantum key distribution protocols for quantum cryptography. These protocols belong to a class of so-called distributed-phase-reference quantum key distribution protocols. While security proofs for some limited attacks exis t, the unconditional security proofs this class of protocol remain unrealised. The existing tools for proving security of protocols ag ainst the most general attacks fail to apply to this class of protocol in a straight forward way. One of the necessary conditions for a quantum key distribution protocol to be secure is the presence of noncommuting measurements. In this paper, the coherent-one-way protocol is formalised, and we describe Bob's measurements by non-commuting POVM elements, showing that this security condition is met.