This paper critically analyzes the Y00 protocol, a quantum noise-based stream cipher proposed to enhance classical cryptographic methods through quantum mechanical properties. Despite its promise, we reveal a structural vulnerability that enables the leakage of secret information from measurement outcomes. To systematically evaluate its security, we first formalize the claims of previously proposed Y00 protocols, clarifying their achievements and limitations. We then identify the structural vulnerability through an intuitive explanation and rigorous formulation using maximum likelihood estimation. Our findings demonstrate that Y00's structural weaknesses allow for the unique determination of the shared secret, leading to significant information leakage. Using the "Toy protocol" as a reference model, we contextualize these results within the broader field of security technology. Furthermore, we generalize our findings to a wider class of quantum-based stream cipher protocols, identifying a fundamental security condition that Y00 fails to satisfy. This condition serves as a critical benchmark for ensuring the security of any stream cipher protocol relying on physical states, whether quantum or classical. These findings underscore the importance of rigorous security evaluations, particularly in systems intended for practical applications. Unexamined vulnerabilities not only undermine trust but also expose systems to avoidable risks, making rigorous analysis indispensable for ensuring resilience and security.

翻译：本文对Y00协议进行了批判性分析，该协议是一种基于量子噪声的流密码，旨在通过量子力学特性增强经典密码学方法。尽管该协议前景广阔，但我们揭示了一种结构性漏洞，该漏洞会导致测量结果泄露秘密信息。为系统评估其安全性，我们首先形式化了先前提出的Y00协议的安全主张，阐明其成果与局限。随后通过直观解释和基于最大似然估计的严格公式化方法，识别出该结构性漏洞。研究结果表明，Y00的结构性缺陷使得共享密钥可被唯一确定，从而导致严重的信息泄露。以"Toy协议"为参考模型，我们将这些结果置于更广泛的安全技术领域进行讨论。此外，我们将研究结论推广至更广泛的量子流密码协议类别，发现Y00协议无法满足一项基本安全条件。该条件构成了评估任何依赖物理状态（无论是量子态还是经典态）的流密码协议安全性的关键基准。这些发现凸显了严格安全评估的重要性，特别是对于拟投入实际应用的系统。未经检验的漏洞不仅会破坏系统可信度，更会使系统暴露于本可避免的风险之中，因此严格的分析对于确保系统韧性与安全性不可或缺。