In this work, we propose a secret key generation procedure specifically designed for the inter-spacecraft communication links. As a novel secrecy source, the spacecrafts utilize Doppler frequency shift based measurements. In this way, the mobilities of the communication devices are exploited to generate secret keys, where this resource can be utilized in the environments that the channel fading based key generation methods are not available. The mobility of a spacecraft is modeled as the superposition of a pre-determined component and a dynamic component. We derive the maximum achievable secret key generation rate from the Doppler frequency shift. The proposed secret key generation procedure extracts the Doppler frequency shift in the form of nominal power spectral density samples (NPSDS). We propose a maximum-likelihood (ML) estimation for the NPSDS at the spacecrafts, then a uniform quantizer is utilized to obtain secret key bits. The key disagreement rate (KDR) is analytically obtained for the proposed key generation procedure. Through numerical studies, the tightness of the provided approximations is shown. Both the theoretical and numerical results demonstrate the validity and the practicality of the presented physical layer key generation procedure considering the security of the communication links of spacecrafts.

中文翻译：

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确保航天器之间的链路安全：多普勒频移产生物理层密钥

在这项工作中，我们提出了专门为航天器之间的通信链路设计的秘密密钥生成程序。作为一种新颖的保密源，这些航天器利用了基于多普勒频移的测量。以这种方式，利用通信设备的移动性来生成秘密密钥，其中可以在基于信道衰落的密钥生成方法不可用的环境中利用该资源。航天器的可移动性被建模为预定组件和动态组件的叠加。我们从多普勒频移中得出最大可实现的秘密密钥生成率。提议的密钥生成过程以标称功率谱密度样本（NPSDS）的形式提取多普勒频移。我们提出了航天器上NPSDS的最大似然（ML）估计，然后利用统一的量化器获得秘密密钥位。对于提议的密钥生成过程，可以通过分析获得密钥不一致率（KDR）。通过数值研究，显示了所提供近似值的紧密度。理论和数值结果都证明了考虑航天器通信链路安全性的物理层密钥生成过程的有效性和实用性。