Limit of quantitative evaluation of the security of quantum key distribution

Jialei Su, Junxuan Liu, Zihao Chen +6 more

Quantum key distribution (QKD) provides information-theoretic security grounded in the fundamental laws of physics. Nevertheless, practical imperfections can introduce side channels that expose QKD systems to quantum hacking, especially passive attacks that are inherently difficult to detect. In this study, we experimentally and theoretically investigate the upper limit of the backflash attack-a representative passive side-channel threat. Using a fully equipped fiber-based QKD receiver, we demonstrate the feasibility of the attack and reveal its limited capability in distinguishing quantum states. We further develop a theoretical framework to quantify the maximum distinguishability achievable by an eavesdropper, taking into account the broadband spectral nature of backflash photons. The analysis shows that Eve can extract effective key information from at most 95.7% of the backflash photons. Based on these findings, we evaluate the secure key rate of a decoy-state BB84 QKD system under backflash attack. Our results provide a quantitative assessment of the vulnerability of QKD systems to backflash emissions and offer a general methodology to evaluate the practical security of QKD systems.

Kiyoshi Tamaki, Go Kato

이충만

X. Chen, Haoze Chen, Fei Xu +10 more

With the rapid development of quantum computing, classical cryptography systems are increasingly vulnerable to security threats, thereby highlighting the urgency of constructing architectures that are resilient to quantum computing attacks. While Quantum Key Distribution (QKD) offers security with information-theoretic guarantees, its relatively low key generation rate necessitates integration with classical cryptographic techniques, particularly block ciphers such as AES and SM4, to facilitate practical applications. However, when a single QKD-key is employed to encrypt multiple data blocks, the reduction in cryptographic security strength has not yet been quantitatively analyzed. In this work, we focus on the security strength in the application scenario where QKD is combined with block ciphers. We propose a quantitative evaluation method for the security benefits of the QKD-key renewal period, aiming to provide a precise measure of the cryptographic security strength in such hybrid systems. Our method is based on concrete security paradigm of block cipher modes of operation. We demonstrate that under practical security level requirements, for files consisting of specific blocks, rekeying k times can provide an additional log2(k) to 2log2(k) bits of security. Our research offers a novel perspective on balancing the security and efficiency of QKD-based encryption.

Yoshimichi Tanizawa, Ririka Takahashi, Hideaki Sato +2 more

Quantum key distribution (QKD), a cryptography technology providing information theoretic security based on physical laws, has moved from the research stage to the engineering stage. Although the communication distance is subject to a limitation attributable to the QKD fundamentals, recent research and development of “key relaying” over a “QKD network” is overcoming this limitation. However, there are still barriers to widespread use of QKD integrated with conventional information systems: applicability and development cost. In order to break down these barriers, this paper proposes a new solution for developing secure network infrastructure based on QKD technology to accommodate multiple applications. The proposed solution introduces 3 functions: (1) a directory mechanism to manage multiple applications hosted on the QKD network, (2) a key management method to share and to allocate the keys for multiple applications, and (3) a cryptography communication library enabling existing cryptographic communication software to be ported to the QKD network easily. The proposed solution allows the QKD network to accommodate multiple applications of various types, and moreover, realizes applicability to conventional information systems easily. It also contributes to a reduction in the development cost per information system, since the development cost of the QKD network can be shared between the multiple applications. The proposed solution was implemented with a network emulating QKD technology and evaluated. The evaluation results show that the proposed solution enables the infrastructure of a single QKD network to host multiple applications concurrently, fairly, and effectively through a conventional application programming interface, OpenSSL API. In addition, the overhead of secure session establishment by the proposed solution was quantitatively evaluated and compared.

Norbert Lütkenhaus