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.

翻译：随着量子计算的快速发展，经典密码体系面临日益严峻的安全威胁，构建抗量子计算攻击的架构显得尤为迫切。量子密钥分发虽能提供信息论可证明的安全性，但其相对较低的密钥生成率需与经典密码技术（特别是AES、SM4等分组密码）结合才能满足实际应用需求。然而，当单个QKD密钥被用于加密多个数据块时，密码安全强度的衰减尚未得到量化分析。本研究聚焦于QKD与分组密码结合的应用场景中的安全强度，提出一种针对QKD密钥更新周期安全增益的量化评估方法，旨在为这类混合系统的密码安全强度提供精确度量。该方法基于分组密码工作模式的具体安全范式。我们证明在实际安全等级要求下，对于由特定数量数据块组成的文件，进行k次密钥更新可提供log2(k)至2log2(k)比特的额外安全性。本研究为平衡基于QKD的加密系统的安全性与效率提供了新的视角。