飞速发展的信息时代对信息安全保护提出了更高的要求，近年来基于量子物理属性的量子密码因其安全高效的优点而受到广泛关注。然而实际量子密钥分发系统往往达不到理想状态，这给实际通信系统带来很多安全性问题。本文首先介绍了基于量子纠缠的Ekert91量子密钥分发协议的原理和基本流程，在此基础上，借鉴基于极化单光子量子密钥分发协议中的特洛伊木马攻击思想，设计了针对纠缠协议的量子黑客攻击方案，同时对攻击思想、攻击原理、攻击步骤以及攻击效果进行了详细的分析。通过验证分析，所提攻击方案针对构成安全密钥的EPR光子对总量的30%进行测量，窃听者可以获得29.25%的安全密钥且只引入0.75%的误码率，具有重要的理论意义和现实可行性。 The rapid development of information age puts forward higher requirements on information se-curity protection. In recent years, quantum cryptography based on the theory of quantum physics gets more and more attention because of its reliability and high efficiency. However, the practical quantum key distribution system often cannot achieve the ideal state, which causes many security problems to the practical communication system. Firstly, this paper introduces the Ekert91 quantum key distribution (QKD) protocol based on quantum entanglement. Then, we propose a partial Trojan-horse attack scheme against this protocol and analyze the theory, process and the effect of the attack. The scheme measures thirty percent of EPR photon pairs used in the formation of security keys, the eavesdropper can obtain twenty-nine point two-five percent of security keys and only causes zero point seven-five percent error rate. The scheme possesses important theoretical significance and realistic feasibility.
飞速发展的信息时代对信息安全保护提出了更高的要求，近年来基于量子物理属性的量子密码因其安全高效的优点而受到广泛关注。然而实际量子密钥分发系统往往达不到理想状态，这给实际通信系统带来很多安全性问题。本文首先介绍了基于量子纠缠的Ekert91量子密钥分发协议的原理和基本流程，在此基础上，借鉴基于极化单光子量子密钥分发协议中的特洛伊木马攻击思想，设计了针对纠缠协议的量子黑客攻击方案，同时对攻击思想、攻击原理、攻击步骤以及攻击效果进行了详细的分析。通过验证分析，所提攻击方案针对构成安全密钥的EPR光子对总量的30%进行测量，窃听者可以获得29.25%的安全密钥且只引入0.75%的误码率，具有重要的理论意义和现实可行性。 The rapid development of information age puts forward higher requirements on information se-curity protection. In recent years, quantum cryptography based on the theory of quantum physics gets more and more attention because of its reliability and high efficiency. However, the practical quantum key distribution system often cannot achieve the ideal state, which causes many security problems to the practical communication system. Firstly, this paper introduces the Ekert91 quantum key distribution (QKD) protocol based on quantum entanglement. Then, we propose a partial Trojan-horse attack scheme against this protocol and analyze the theory, process and the effect of the attack. The scheme measures thirty percent of EPR photon pairs used in the formation of security keys, the eavesdropper can obtain twenty-nine point two-five percent of security keys and only causes zero point seven-five percent error rate. The scheme possesses important theoretical significance and realistic feasibility.
Abstract Most security proofs of quantum key distribution (QKD) disregard the effect of information leakage from the users’ devices, and, thus, do not protect against Trojan-horse attacks (THAs). In a THA, the eavesdropper injects strong light into the QKD apparatuses, and then analyzes the back-reflected light to learn information about their internal setting choices. Only a few recent works consider this security threat, but predict a rather poor performance of QKD unless the devices are strongly isolated from the channel. Here, we derive finite-key security bounds for decoy-state-based QKD schemes in the presence of THAs, which significantly outperform previous analyses. Our results constitute an important step forward to closing the existing gap between theory and practice in QKD.
Quantum key distribution (QKD) leverages the principles of quantum mechanics to provide theoretically unconditional security for cryptographic key sharing. However, practical implementations remain vulnerable due to potential security loopholes at both the source and detection sides of QKD systems. The side-channel-secure (SCS) protocol addresses these challenges by encoding bits in vacuum and non-vacuum states and introducing a third-party measurement node, thereby repelling attacks targeting the detection side as well as external lab attacks on the source side. In this work, we consider the state-dependent correlated errors and Trojan-horse attack while preserving the SCS protocol’s key advantage—-specifically, requiring only upper bounds on intensity characterization without needing a full description of quantum states in infinite dimensions. Numerical results demonstrate that when the reflected light intensity from Trojan-horse attacks falls below 10 −6 , Eve can scarcely extract additional key information from the reflections. This work makes the SCS protocol more practical.
Quantum key distribution (QKD), which theoretically provides unconditional secure communication, has developed rapidly in the past decades. However, the practical QKD systems still have vulnerabilities due to device imperfections. Polarization-encoding systems are one of the most important branches in the field of QKD. To date, a variety of polarization-encoding schemes have been proposed to meet the requirements of high speed and robust modulation, but the security analysis of these schemes is often ignored. In this paper, we experimentally and theoretically evaluated the security of three typical polarization encoders against the Trojan horse attack (THA), which is recognized as one of the critical quantum attacks. We built a system to implement the THA and collected the reflection from QKD configuration with different encoders. According to the experimental results, we further analyzed the secure key rate and the resistance against THAs of the system while BB84 or measurement-device-independent QKD was applied. Our paper plays an important guiding role in the design of polarization encoders and the construction of secure QKD systems with realistic devices.
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.
Realistic experimental apparatus of quantum cryptography are imperfect, which may be utilized by a potential eavesdropper to eavesdrop on the communication. We show that quantum communication may be improved with quantum teleportation and entanglement swapping, which is robustly secure against the most general Trojan horse attacks. Our scheme is not an improvement of the communication apparatus, but the improvement of quantum communication protocol itself. We show that our modified schemes may be implemented with current technology.
Abstract Early security proofs of the keys in quantum cryptography systems were based on the assumption that the transmitting and receiving stations were completely isolated from the outside world—the eavesdropper. However, this condition cannot be implemented in practice, since quantum cryptography systems are open systems, in the sense that an eavesdropper can have indirect access, for example, through a fiber communication channel to critical equipment elements (phase modulators, intensity modulators, etc) using active sensing of the state of these elements—Trojan-horse attacks. A new Trojan-horse attack based on joint unambiguous measurements of reflected probing states from an intensity modulator and information states in a quantum communication channel is proposed. Estimates of attack parameters for a number of quantum key distribution protocols are given, when an attack leads to compromise of keys.