Quantum-key-distribution (QKD) networks are gaining importance and it has become necessary to analyze the most appropriate methods for their long-distance interconnection. In this paper, four different methods of interconnecting remote QKD networks are proposed. The methods are used to link three different QKD testbeds in Europe, located in Berlin, Madrid, and Poznan. Although long-distance QKD links are only emulated, the used methods can serve as a blueprint for a secure interconnection of distant QKD networks in the future. Specifically, the presented approaches combine, in a transparent way, different fiber and satellite physical media, as well as common standards of key-delivery interfaces. The testbed interconnections are designed to increase the security by utilizing multipath techniques and multiple hybridizations of QKD and post quantum cryptography (PQC) algorithms.

翻译：量子密钥分发（QKD）网络的重要性日益凸显，分析其长距离互联的最优方法已成为必要。本文提出四种远程QKD网络的互联方法，并用于连接分别位于柏林、马德里和波兹南的三个欧洲QKD测试平台。尽管长距离QKD链路仅为仿真实现，但所采用的方法可为未来安全互联远程QKD网络提供蓝图参考。具体而言，本文方案以透明方式融合了不同光纤与卫星物理介质，以及通用的密钥交付接口标准。测试平台互联设计通过利用多路径技术、QKD与后量子密码（PQC）算法的多种混合方式来增强安全性。