Quantum cryptography studies the unconditional information security against an all-powerful eavesdropper in secret key distillation. However the assumption of an omnipotent eavesdropper is too strict for some realistic implementations. In this paper we study the realistic application model of secret key distillation over satellite-to-satellite free space channel in which we impose a reasonable restriction on the eavesdropper by setting an exclusion zone around the legitimate receiver as a defense strategy. We first study the case where the eavesdropper's aperture size is unlimited so her power is only restricted by the exclusion zone. Then we limit Eve's aperture to a finite size and study the straightforward case when her aperture is in the same plane of Bob, investigating how an exclusion zone can help improve security. Correspondingly, we determine the secret key rate lower bounds as well as upper bounds. Further more, we also apply our results on specific discrete variable (DV) and continuous variable (CV) protocols for comparison. We show that by putting reasonable restrictions on the eavesdropper through the realistic assumptions of an inaccessible exclusion zone, we can increase the key rate in comparison to those without and do so with relatively lower transmission frequency. We conclude that this model is suitable for extended analysis in many light gathering scenarios and for different carrier wavelengths.

中文翻译：

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现实卫星到卫星自由空间信道上的秘密密钥蒸馏：禁区分析

量子密码学研究在秘密密钥蒸馏中无条件地防止全能窃听者的信息安全。然而，对于一些现实的实现来说，全能窃听者的假设过于严格。在本文中，我们研究了在卫星到卫星自由空间信道上秘密密钥蒸馏的现实应用模型，其中我们通过在合法接收器周围设置禁区作为防御策略来对窃听者施加合理的限制。我们首先研究窃听者的孔径大小不受限制，因此她的权力仅受禁区限制的情况。然后我们将 Eve 的孔径限制为有限大小，并研究当她的孔径与 Bob 处于同一平面时的简单情况，研究禁区如何帮助提高安全性。相应地，我们确定密钥率下限和上限。此外，我们还将我们的结果应用于特定离散变量 (DV) 和连续变量 (CV) 协议以进行比较。我们表明，通过不可访问的禁区的现实假设对窃听者施加合理的限制，与没有禁区的人相比，我们可以提高密钥率，并以相对较低的传输频率这样做。我们得出结论，该模型适用于在许多光收集场景和不同载波波长下进行扩展分析。我们表明，通过不可访问的禁区的现实假设对窃听者施加合理的限制，与没有禁区的人相比，我们可以提高密钥率，并以相对较低的传输频率这样做。我们得出的结论是，该模型适用于在许多聚光场景和不同载波波长中进行扩展分析。我们表明，通过不可访问的禁区的现实假设对窃听者施加合理的限制，与没有禁区的人相比，我们可以提高密钥率，并以相对较低的传输频率这样做。我们得出的结论是，该模型适用于在许多聚光场景和不同载波波长中进行扩展分析。