Quantum key distribution (QKD) offers unconditional security but existing QKD networks remain difficult to scale across heterogeneous infrastructures and administrative domains due to vendor-specific interfaces, trusted-node constraints, and limited interoperability. This work presents a flexible multi-domain and multi-site quantum-secure network architecture integrating vendor-agnostic QKD, SDN orchestration, and cloud-managed trust services. Communication is based on Zero Trust Network Access protocols featuring multi-level authentication mechanisms building upon post-quantum cryptography (PQC) signature and key encapsulation algorithms. The system is deployed on a real-world testbed with domains incorporating QKD nodes from 3 vendors, as well as domains without QKD infrastructure elements. Experimental results show that PQC and SDN overhead remain relatively low even on constrained devices, with the main bottleneck being QKD key retrieval and vendor-specific key streaming limitations. The proposed framework extends quantum-safe key transport beyond native QKD boundaries while preserving flexibility, interoperability, and compatibility with existing infrastructures.
Quantum key distribution (QKD) offers unconditional security but existing QKD networks remain difficult to scale across heterogeneous infrastructures and administrative domains due to vendor-specific interfaces, trusted-node constraints, and limited interoperability. This work presents a flexible multi-domain and multi-site quantum-secure network architecture integrating vendor-agnostic QKD, SDN orchestration, and cloud-managed trust services. Communication is based on Zero Trust Network Access protocols featuring multi-level authentication mechanisms building upon post-quantum cryptography (PQC) signature and key encapsulation algorithms. The system is deployed on a real-world testbed with domains incorporating QKD nodes from 3 vendors, as well as domains without QKD infrastructure elements. Experimental results show that PQC and SDN overhead remain relatively low even on constrained devices, with the main bottleneck being QKD key retrieval and vendor-specific key streaming limitations. The proposed framework extends quantum-safe key transport beyond native QKD boundaries while preserving flexibility, interoperability, and compatibility with existing infrastructures.
Cloud infrastructures moving toward post-quantum cryptography present both opportunities and risks since safe workload interoperability is made more difficult by disparate providers' uneven key management. In this study, a crypto-agile zero-trust access architecture for multi-cloud environments is presented, utilizing software-defined networking (SDN) to coordinate quantum key distribution (QKD) and post-quantum cryptography (PQC) for session security. The architecture incorporates a policy-driven controller that uses programmable data planes for micro-segmentation and continuous verification to dynamically choose ML-KEM or QKD-derived keys for each transaction. The system includes automated failover between PQC and QKD to guarantee resilience, preserving secure connectivity in the event of link failure or resource exhaustion. QKD-PQC failover under adversarial stress, flow-level path enforcement via P4, and TLS 1.3 handshakes with PQC are all demonstrated using a simulation prototype. The results demonstrate that SDN-based orchestration can maintain performance and uphold zero-trust principles, while also highlighting the viability of quantifying PQC overhead in real-time cloud scenarios. This establishes the framework as a workable route to multi-cloud security that is quantum robust.
The ongoing transition toward quantum-safe networking has motivated the development of hybrid network architectures integrating Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC). However, the experimental evaluation of hybrid QKD-PQC network architectures remains constrained by the high cost and limited accessibility of quantum hardware, as well as by the limited support for hybrid QKD-PQC networks in existing emulation platforms. Quditto is an open-source emulation platform originally designed for QKD networks that enables cost-effective and reproducible experimentation without requiring dedicated physical quantum infrastructure. Building on this foundation, this work presents Quditto as a hybrid QKD-PQC network emulation platform featuring automated and scalable cloud-native orchestration. The proposed platform introduces four principal contributions: a cloud-native orchestrator enabling fully automated infrastructure deployment across cloud and multi-cluster environments; an optimized provisioning workflow enabling large-scale quantum-safe network emulation; native integration of post-quantum nodes enabling unified emulation of hybrid QKD-PQC networks; and a secure key management module providing persistent and access-controlled storage of cryptographic material. Experimental validation demonstrates sublinear orchestration-time scaling with network size and successful end-to-end hybrid QKD-PQC key establishment on a representative spine-leaf deployment, thereby enabling the systematic evaluation of quantum-safe networking mechanisms in large-scale heterogeneous network environments.
A multi-vendor, multi-domain Quantum Key Distribution network comprising 15 nodes across three independently managed domains was deployed and operated during QCI Days 2025 in Athens. The large-scale field trial integrated heterogenous QKD technologies, multi-layer Key Management Systems, and SDN-controlled infrastructures into a unified inter-domain architecture enabling cross-domain key exchange and coordination. The setup combined in-rack domain nodes extended to a 4-node field-deployed metropolitan QKD network segment, providing a realistic operational environment for validating end-to-end functionality. Multiple QKD-enabled services were successfully supported across the federated infrastructure, proving the technical feasibility and viability of scalable QKD deployments in inter-domain settings.
The importance of quantum-key-distribution (QKD) networks is growing rapidly, not only because the underlying QKD protocol is immune against any (known or unknown) attacks but also as these infrastructures can be operated in a hybrid mode, together with emerging quantum safe, or post quantum cryptography (PQC), public key protocols. Hybrid solutions appear to be the most promising remedy against real-world security risks, posed by prospective quantum computers. Simultaneously, telecommunication operators are embracing novel network paradigms, such as software-defined networking (SDN), due to distinct advantages over traditional approaches. SDN-inspired architectures can also be used for QKD and hybrid QKD-PQC networks. These architectures allow a seamless integration of QKD and hybrid QKD-PQC into production networks, significantly increasing the security of the latter. However, there has only been very limited research on optimal strategies for establishing hybrid connectivity across different organizational domains. The present contribution introduces two methods on interconnecting different technological and administrative domains for such networks. The proposed scheme is QKD-vendor independent and relies heavily on standard and open interfaces. It enables a complete end-to-end communication between applications running on nodes in different domains. It can be used for the secure interconnection of different SDN-based telecommunication domains with additional QKD / hybrid protection and has been tested within the Madrid Quantum-Communication Infrastructure.
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.
Abstract: This study advances a unifying systems perspective on quantum-safe network security by synthesizing recent progress in quantum cryptography with practical integration patterns across carrier-grade infrastructures. Concept analysis distinguishes the roles of quantum key distribution (QKD), device-independent variants, quantum authentication, and post-quantum cryptography (PQC) within zero-trust architectures. Building on this, a layered framework—spanning physical/entanglement resources, key management, crypto-agility, control plane orchestration, and policy/compliance—is articulated to support end-to-end, composable guarantees. The problem addressed is the realization of verifiable, quantum-resilient security under operational constraints involving latency, key-rate variability, and heterogeneous trust assumptions. Methodology combines a structured literature synthesis with formal composability mapping to universal composability principles, adversarial threat modeling for quantum-enabled attackers, and testbed/simulation evaluation of hybrid QKD–PQC pipelines across L2–L3 segments and 5G/6G backhaul scenarios. Key results indicate that (i) selective QKD deployment on high-value links coupled with PQC at endpoints enhances resilience while preserving crypto-agility; (ii) automated key-lifecycle orchestration reduces exposure windows; and (iii) device-independent assurances strengthen guarantees where trust relaxation is necessary. The impact is a deployment-ready reference architecture, measurable integration metrics, and guidance aligned with emerging standards for critical infrastructure and national networks. The implications extend to procurement, compliance, and roadmap planning for quantum-era network security. Keywords: quantum-safe cryptography, quantum key distribution (QKD), post-quantum cryptography (PQC), hybrid QKD–PQC, composable security, device-independent QKD, zero-trust networks, key management and orchestration, 5G/6G backhaul, network security architecture, standards and interoperability