Operational Architecture of National QKD Backbone

Anne de Chastenet, Eric Augé, Gonzague Reydet +3 more

Aagnik Chakraborty

Cryptographically relevant quantum computers do not yet exist, but the transition away from classical public-key cryptography is already underway: adversaries can record encrypted traffic today and decrypt it once a sufficiently capable quantum computer becomes available, a threat known as harvest-now, decrypt-later. This paper examines the engineering case for combining post-quantum cryptography (PQC) with quantum key distribution (QKD) as a strategy for securing next-generation communication infrastructure, focusing on 6G core and radio-access networks, Open RAN (O-RAN), and constrained Internet of Things (IoT) deployments. Rather than treating the two mechanisms as symmetric, interchangeable layers, the paper examines what each one actually guarantees, surveys the empirical evidence available for deployment cost, and describes where national security authorities and standards bodies disagree on the value of QKD. The architecture is grounded in the finalized National Institute of Standards and Technology (NIST) PQC standards and its 2025 hybrid key-establishment guidance, drawing on empirical Open RAN latency and energy measurements published during 2025 and 2026, embedded-hardware benchmarks for constrained devices, and the small number of quantum key distribution deployments operating at metropolitan or national backbone scale today. The paper is explicit about which figures are measured results and which remain illustrative proposals, and it closes by naming the specific standardization and field-trial gaps that separate current practice from the architecture it describes. The purpose of the work is to give network architects and policymakers a single, evidence-graded reference for deciding where each mechanism belongs in a real deployment, rather than treating post-quantum and quantum-distributed keying as equivalent options.

Sebastian Raubitzek, Werner Strasser, Sebastian Ramacher +3 more

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.

Ramona Wolf

Salvatore Virzì, Alice Meda, Cecilia Clivati +6 more

Quantum key distribution (QKD) is a technology that allows sharing secret cryptographic keys between two distant users (Alice and Bob), whose intrinsic security is guaranteed by fundamental principles of quantum mechanics. QKD is a mature technology: in Europe, all the 27 EU member states are working in a European Commission initiative (EuroQCI) to design, develop and deploy a quantum communication infrastructure composed by several national networks. For example, in Italy, the Italian Quantum Backbone will be used as a quantum communication testbed within the project QUID, that is in charge of the realization of the Italian part of EuroQCI.

Fabrizio Lo Regio, Matteo D’Iorio, Mauro D’Arco +1 more