Abstract Considering the rapid development of quantum technology, it has become inevitable to use this technology to develop an ultimately secured key exchange system. Quantum key distribution (QKD) technology has become more sophisticated, is expected to provide secure key distribution mechanism for the actual information security systems. The unique advantage of quantum cryptography is precisely its ability to guarantee absolute security. Previous works have demonstrated unconditional security of the ideal BB84 QKD system. However, on a typical QKD system, many practical situations often cannot satisfy the requirements of the ideal condition. This problem causes some security issues for practical QKD system. Therefore, it is necessary to analyze the security of QKD system under practical conditions, and identify the security implications on the practical physical systems and equipment, in order to find a method that guarantees the security of QKD system. The security of QKD system based on BB84 involves many aspects; this paper mainly focuses on how to resolve security issues that may exist, especially in the BB84 protocol post-processing. We introduce ways to tackle these issues and make vital key information leakage very small. Their impact on the security of entire QKD system is analyzed, and the interaction and security optimization between the various parts is researched. Finally, the thesis briefly introduces five sub-modules of post-processing of QKD system: the base comparison, error estimation, information correction, data check and privacy amplification; the existent security factors of each module is given, for error estimation and information correction is provided the secure model with those issues. Thus, the security model of post-processing is further optimized.
Abstract Considering the rapid development of quantum technology, it has become inevitable to use this technology to develop an ultimately secured key exchange system. Quantum key distribution (QKD) technology has become more sophisticated, is expected to provide secure key distribution mechanism for the actual information security systems. The unique advantage of quantum cryptography is precisely its ability to guarantee absolute security. Previous works have demonstrated unconditional security of the ideal BB84 QKD system. However, on a typical QKD system, many practical situations often cannot satisfy the requirements of the ideal condition. This problem causes some security issues for practical QKD system. Therefore, it is necessary to analyze the security of QKD system under practical conditions, and identify the security implications on the practical physical systems and equipment, in order to find a method that guarantees the security of QKD system. The security of QKD system based on BB84 involves many aspects; this paper mainly focuses on how to resolve security issues that may exist, especially in the BB84 protocol post-processing. We introduce ways to tackle these issues and make vital key information leakage very small. Their impact on the security of entire QKD system is analyzed, and the interaction and security optimization between the various parts is researched. Finally, the thesis briefly introduces five sub-modules of post-processing of QKD system: the base comparison, error estimation, information correction, data check and privacy amplification; the existent security factors of each module is given, for error estimation and information correction is provided the secure model with those issues. Thus, the security model of post-processing is further optimized.
Quantum key distribution (QKD) is a method that enables secure communication between two parties by applying the ideas of quantum physics. By minimizing information leakage that can happen during the key generation process, privacy amplification is a technique used to improve the security of QKD. The technique involves processing the raw key obtained from QKD through a randomization procedure to remove any residual information that may have been leaked during the quantum transmission. While privacy amplification can significantly improve the security of QKD, the effectiveness of the technique is limited by the quality of the initial raw key. The BB84 QKD protocol has been improved with the proposed En-BB84 protocol, which includes built-in authentication and integrity checks. The En-BB84 protocol ensures secure distribution of secret keys and protects against tampering by attackers. Key distillation and error correction techniques are employed to extract a shorter, more secure shared secret key and correct errors introduced during qubit transmission. The protocol utilizes a four-state QKD approach, expanding on the traditional two-state scheme of BB84. A simulation of the En-BB84 protocol is demonstrated using a quantum circuit implemented with Qiskit in Python. The circuit employs various gates and operations, including Hadamard, CX, controlled swap, and RZ gates, to achieve encoding and error correction. Furthermore, we have designed a better protocol with improved error rates by incorporating improvisations on the BB84 protocol. Experimental results indicate the successful integration of the B92 error correction scheme into the modified BB84 protocol, enhancing the security and performance of QKD systems.
Quantum Key Distribution (QKD) is a technique that enables secure communication between two parties by sharing a secret key. One of the most well-known QKD protocols is the BB84 protocol, proposed by Charles Bennett and Gilles Brassard in 1984. In this protocol, Alice and Bob use a quantum channel to exchange qubits, allowing them to generate a shared key that is resistant to eavesdropping. This paper presents a comparative study of existing QKD schemes, including the BB84 protocol, and highlights the advancements made in the BB84 protocol over the years. The study aims to provide a comprehensive overview of the different QKD schemes and their strengths and weaknesses and demonstrate QKDs working principles through existing simulations and implementations. Through this study, we show that the BB84 protocol is a highly secure QKD scheme that has been extensively studied and implemented in various settings. Furthermore, we discuss the improvements made to the BB84 protocol to enhance its security and practicality, including the use of decoy states and advanced error correction techniques. Overall, this paper provides a comprehensive analysis of QKD schemes, focusing on the BB84 protocol in secure communication technologies.
Quantum key distribution (QKD) technology is a frontier in the field of secure communication, leveraging the principles of quantum mechanics to offer information-theoretically secure keys. Postprocessing is an important part of a whole QKD system because it directly impacts the secure key rate and the security of the system. In particular, with the fast increase in the photon transmission frequency in a QKD system, the processing speed of postprocessing becomes an essential issue. Our study embarks on a comprehensive review of the development of postprocessing of QKD, including five subprotocols, namely, parameter estimation, sifting, information reconciliation, privacy amplification, and channel authentication. Furthermore, we emphasize the issues raised in the implementation of these subprotocols under practical scenarios, such as limited computation or storage resources and fluctuations in channel environments. Based on the composable security theory, we demonstrate how enhancements in each subprotocol influence the secure key rate and security parameters, which can provide meaningful insights for future advancements in QKD.
Key distillation, also referred to as classical post-processing, plays a pivotal role in Quantum Key Distribution (QKD) protocols. Key distillation encompasses numerous subroutines, making the analysis of its overall security implications potentially challenging for those outside the research community. In this paper, we elucidate the role of the key distillation phase in QKD from a security standpoint. We begin by analyzing the different components of the key distillation phase individually, followed by an examination of the process as a whole. We then calculate the bit strength of the produced key, assuming that an attacker is executing an intercept and resend attack. For our analysis, we employ a practical key distillation implementation linked to a decoy state BB84 protocol as a case study. Our findings suggest that the security of the final key, post the key distillation phase, hinges on several factors. These include the theoretical security of the implemented subroutines, the total information leakage throughout the process, and the choices of subroutine parameters. Given these assumptions, we can distill 287 secure bits for every 1000 bits that undergo the key distillation procedure.
Quantum cryptography, or, more precisely, quantum key distribution (QKD) allows two distant parties, Alice and Bob, to expand a previously shared secret key by sending quantum states through a quantum channel. The goal here is for Alice and Bob to communicate securely in the presence of an eavesdropper, Eve. The most well-known QKD protocol is the Bennett-Brassard 1984 (BB84) protocol, which has been proved unconditionally secure against any attacks allowed by quantum mechanics. The main advantage of QKD over conventional cryptography is its absolute security. Thus, it is imperative to evaluate the security and performance of QKD protocols and realistic QKD systems. In this thesis, we study the security and performance aspects of QKD in four parts. In the first part, we study the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocol. This protocol differs from the BB84 protocol only in the classical post-processing step and uses the same four quantum states as the BB84 protocol. We compared these two protocols and showed that in typical situations, the classical post-processing software for BB84 should be used in order to have a higher performance. In the second part, we prove the security of a three-state protocol. This protocol is similar to the BB84 protocol in that they share the same three qubit states. In the third part, we consider a practical Trojan horse attack on practical QKD systems implementing the BB84 protocol. The attack works by taking advantage of the finite response time of practical phase modulators to remap the states sent out by the legitimate user, Alice. We showed that if Alice and Bob are unaware of our attack, the final key shared between them can be compromised in some situations. In the fourth part, we consider another type of Trojan horse attack, which is based on mismatch between detection efficiencies of detectors. Practical detectors in QKD systems usually do not have identical efficiencies and an eavesdropper Eve may be able to exploit this efficiency mismatch to steal information about the final secret key. We analyze the security of the attack and show that it is possible for Eve to acquire some information on the final secret key if Alice and Bob are unaware of this attack.
Cryptography is crucial to protect sensitive data. Traditional cryptography relies on mathematical difficulty to secure valuable data against intruders. However, with the rise of quantum computers, these assumptions are threatened as quantum computers can process information much faster. The security models need to be upgraded to withstand quantum computers. RSA and ECC, two common asymmetric cryptosystems, have been upgraded using post-quantum cryptography (PQC). Another solution might be to leverage the principles of quantum mechanics to ensure secure communication. The most common application of quantum cryptography is quantum key distribution (QKD), which solves the key exchange problem using quantum physics, complementing conventional cryptographic techniques by enabling secure key generation, while classical methods remain necessary for authentication and protocol implementation. QKD is secure in theory, but practical implementations often differ from theory due to imperfect devices. An intruder can find loopholes and vulnerabilities to attack the QKD systems and jeopardize its security. In this thesis, current knowledge of these attacks has been reviewed and simulated on two different QKD protocols. The simulations highlight the importance of researching the attacks and implementing countermeasures.