Andreas Neuhold

Paul Spooren, Andreas Neuhold, Sebastian Ramacher et al.

We present a layered and modular network architecture that combines Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC) to provide scalable end-to-end security across long distance multi-hop, trusted-node quantum networks. To ensure interoperability and efficient practical deployment, hop-wise tunnels between physically secured nodes are protected by WireGuard with periodically rotated pre-shared keys sourced via the ETSI GS QKD 014 interface. On top, Rosenpass performs a PQC key exchange to establish an end-to-end data channel without modifying deployed QKD devices or network protocols. This dual-layer composition yields post-quantum forward secrecy and authenticity under practical assumptions. We implement the design using open-source components and validate and evaluate it in simulated and lab test-beds. Experiments show uninterrupted operation over multi-hop paths, low resource footprint and fail-safe mechanisms. We further discuss the design's compositional security, wherein the security of each individual component is preserved under their combination and outline migration paths for operators integrating QKD-aware overlays in existing infrastructures.

Sebastian Raubitzek, Werner Strasser, Sebastian Ramacher et al.

The European Union is developing the European Quantum Communication Infrastructure (EuroQCI) as a pan-European network to provide secure communication capabilities across Member States, including governmental and critical-infrastructure domains. While the strategic objective is defined at EU level, the required scale and structure of national quantum key distribution (QKD) networks remain largely unspecified. This work addresses the question of how to plan and size national terrestrial QKD networks to support critical infrastructure and public authorities. We propose a reproducible planning methodology that estimates network size, total fiber length, and the number of required QKD components based on a small set of explicit assumptions. The approach is demonstrated for Austria, where a synthetic but structured network model is constructed and evaluated using Monte Carlo simulation. The model focuses on terrestrial QKD infrastructure and explicitly excludes space-based segments. It estimates endpoint counts, trusted repeater node requirements, and hop-length distributions under realistic operational constraints. The Austrian case is then used as a baseline to derive scaling rules for other EU Member States based on population and geographic extent. The results provide first-order planning estimates for national QKD backbone sizes across Europe. These estimates are not intended as deployment designs but as planning-level references that support early-stage cost assessment and infrastructure dimensioning under the EuroQCI framework.