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）网络日益重要，分析其长距离互联的最优方法已成为必要。本文提出四种互联远程QKD网络的方法，并用于连接位于柏林、马德里和波兹南的三个欧洲QKD测试平台。尽管仅模拟了长距离QKD链路，但所用方法可为实现未来远距离QKD网络的安全互联提供蓝图。具体而言，所提方法以透明方式融合了不同光纤与卫星物理介质，以及密钥分发接口的通用标准。测试平台的互联设计通过采用多路径技术及QKD与后量子密码（PQC）算法的多种混合方式，旨在提升安全性。