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arxiv: 2604.20376 · v1 · submitted 2026-04-22 · 💻 cs.NI

Interconnecting Regional QKD Networks: Hybrid Key Delivery Across Quantum Domains

David Barral , Aitor Brazaola-Vicario , Diego Cifri\'an , Natalia Costas , Gonzalo Bl\'azquez , Ana Fern\'andez-Vilas , Iago F. Llovo , Pedro Otero-Garc\'ia
show 4 more authors
Pablo P. Rejo Alejandra Ruiz Juan Villasuso Manuel Fern\'andez-Veiga
This is my paper

Pith reviewed 2026-05-09 23:51 UTC · model grok-4.3

classification 💻 cs.NI
keywords QKDhybrid key deliverypost-quantum cryptographyquantum networkskey relayWAN interconnectiontestbed implementation
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The pith

Regional QKD networks interconnect by relaying keys with post-quantum cryptography over classical links.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper develops a hybrid key delivery service to link separate QKD subnetworks across wide areas. It generates secret keys locally using QKD within each domain and relays them securely to other domains using post-quantum cryptography such as Kyber over standard classical network connections. The design is distributed and includes dynamic routing of keys at the system level. The approach has been built and tested in an operational setup with three regional subnetworks, providing performance measurements that demonstrate its scalability for key distribution services.

Core claim

The authors present a standards-driven design for a unified hybrid key delivery service that connects isolated QKD domains via classical WAN links. Keys are generated within each domain using QKD and then relayed using PQC algorithms like Kyber, with dynamic routing and system-level management. This solution has been implemented in a testbed of three regional subnetworks, where design principles, deployment details, and experimental performance results are shown for the scalable service.

What carries the argument

The hybrid key relay using post-quantum cryptography to forward QKD-generated keys between domains over classical links.

If this is right

  • The service enables interconnection of regional QKD networks without direct long-distance quantum links.
  • Dynamic routing allows flexible key delivery across the system.
  • Experimental results from the three-subnetwork testbed validate the performance and scalability.
  • The design follows standards for potential broader adoption.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Such hybrid systems may allow QKD to be deployed more widely by leveraging existing classical infrastructure for long-haul transport.
  • The testbed results suggest potential for extension to larger numbers of domains or integration with other network services.
  • Security assumptions about the PQC relay would need ongoing validation as quantum threats evolve.

Load-bearing premise

Relaying the QKD keys via PQC over classical WAN links does not introduce security vulnerabilities from the relay mechanism or implementation details.

What would settle it

A security breach in the relayed keys or key rates too low for practical use in the three-subnetwork testbed would show the hybrid approach fails to preserve security and scalability.

Figures

Figures reproduced from arXiv: 2604.20376 by Aitor Brazaola-Vicario, Alejandra Ruiz, Ana Fern\'andez-Vilas, David Barral, Diego Cifri\'an, Gonzalo Bl\'azquez, Iago F. Llovo, Juan Villasuso, Manuel Fern\'andez-Veiga, Natalia Costas, Pablo P. Rejo, Pedro Otero-Garc\'ia.

Figure 1
Figure 1. Figure 1: Workflow and message exchange between the KMSTN entities and the SAEs for a key request. [PITH_FULL_IMAGE:figures/full_fig_p011_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Map and network topology of our testbed, spanning the regions of Galicia and the Basque Country, in Northern [PITH_FULL_IMAGE:figures/full_fig_p014_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Configuration for the testbed measurements. [PITH_FULL_IMAGE:figures/full_fig_p016_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Statistics of the keyrate for two nodes. KMSTN1 (left) and KMSTN7 (right) [PITH_FULL_IMAGE:figures/full_fig_p019_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Statistics of delay for several nodes. link and are capable of attaining only around 500 b/s for the SKR. The distribution of the keyrates ( [PITH_FULL_IMAGE:figures/full_fig_p020_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Latency of key requests in ms. Values are averaged over a [PITH_FULL_IMAGE:figures/full_fig_p021_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Latency of concurrent key requests vs. time. Each point is a measure of delay, and the vertical slices correspond [PITH_FULL_IMAGE:figures/full_fig_p022_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Pairwise correlation matrix between the metrics collected in the experiments. [PITH_FULL_IMAGE:figures/full_fig_p023_8.png] view at source ↗
read the original abstract

QKD technology is being increasingly adopted inside the network core for protecting information transport against any form of computational attacks. However, the use of QKD for wide-area internetworking is still challenging and costly, due to its strong trust assumptions and the low achievable key rates in long QKD links. This paper presents a standards-driven design and implementation of a unified hybrid key delivery service for a network of isolated QKD domains (subnetworks using QKD as provider technology for secret key generation) connected via classical WAN links. The framework follows a distributed architecture and uses a hybrid approach where keys generated in a domain are securely relayed to other domains with PQC (Kyber), dynamically routed, and managed at the system level. The solution has been implemented in an operational testbed comprising three regional subnetworks. We present the design principles, the deployment, and the experimental performance results for this scalable key delivery service.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The paper describes a standards-driven hybrid key delivery architecture for interconnecting isolated QKD domains over classical WAN links. Keys generated via QKD within each regional subnetwork are relayed using Kyber (PQC) with dynamic routing and system-level management. The design is implemented in an operational testbed spanning three regional subnetworks, and the manuscript presents the deployment details together with experimental performance results for the resulting scalable key delivery service.

Significance. If the hybrid relay mechanism can be shown to preserve end-to-end security, the work would offer a pragmatic path to scaling QKD beyond single domains by exploiting existing classical infrastructure. The concrete testbed deployment with three subnetworks constitutes a useful engineering demonstration of feasibility and interoperability for quantum networking.

major comments (2)
  1. [Abstract / Architecture description] The central claim that keys are 'securely relayed' across domains rests on the hybrid PQC relay preserving the security properties of the original QKD keys. No security model, threat analysis, or reduction is provided anywhere in the manuscript to substantiate this (see abstract and the description of the relay mechanism).
  2. [Experimental results] The experimental results are presented without quantitative metrics, error bars, baseline comparisons, or statistical analysis, which prevents assessment of whether the observed performance supports the scalability claims (see the testbed results section).

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments on our manuscript. We address each major point below and will revise the paper to strengthen the security discussion and the presentation of experimental results.

read point-by-point responses

  1. Referee: [Abstract / Architecture description] The central claim that keys are 'securely relayed' across domains rests on the hybrid PQC relay preserving the security properties of the original QKD keys. No security model, threat analysis, or reduction is provided anywhere in the manuscript to substantiate this (see abstract and the description of the relay mechanism).

    Authors: We agree that the manuscript would benefit from an explicit security discussion. The design assumes the information-theoretic security of QKD within each domain and the computational security of Kyber for the WAN relay, with relays trusted to forward but not to learn the keys. In the revised manuscript we will add a dedicated subsection in the architecture section that states the threat model (honest-but-curious inter-domain relays, no collusion with domain-internal QKD nodes), lists the security assumptions, and explains why the hybrid composition preserves end-to-end confidentiality. We will also cite Kyber’s security proofs and note that a full reduction proof lies outside the scope of this engineering-focused paper. revision: yes

  2. Referee: [Experimental results] The experimental results are presented without quantitative metrics, error bars, baseline comparisons, or statistical analysis, which prevents assessment of whether the observed performance supports the scalability claims (see the testbed results section).

    Authors: We acknowledge that the current testbed results section presents performance data primarily through figures without accompanying numerical tables, error bars, or statistical treatment. In the revision we will expand this section with a table of measured key-delivery rates, relay latencies, and overheads (including standard deviations from repeated runs), direct comparisons to single-domain QKD baselines, and a brief discussion of how these metrics scale with the number of domains. This will allow readers to evaluate the scalability claims more rigorously. revision: yes

Circularity Check

0 steps flagged

No circularity: engineering design and experimental report with no derivations

full rationale

The paper presents a standards-driven design, implementation, and experimental evaluation of a hybrid QKD-PQC key relay architecture across regional domains. It describes a distributed system with dynamic routing, reports deployment in a three-subnetwork testbed, and gives performance results. No equations, fitted parameters, uniqueness theorems, or derivation chains appear in the provided text. The central claims concern functionality, scalability, and measured performance rather than any result derived from prior inputs by construction. Any self-citations (if present) are not load-bearing for a mathematical argument because no such argument exists. The absence of a formal security reduction is a completeness concern, not evidence of circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard assumptions about QKD security within domains and PQC security for classical relay channels, with no free parameters, invented entities, or ad-hoc axioms introduced.

axioms (2)
  • domain assumption QKD provides information-theoretically secure keys within isolated domains
    Invoked as the foundation for local key generation in the hybrid service.
  • domain assumption Kyber PQC provides secure key encapsulation over classical WAN links
    Used to justify secure relaying of keys between domains.

pith-pipeline@v0.9.0 · 5514 in / 1175 out tokens · 24695 ms · 2026-05-09T23:51:31.947602+00:00 · methodology

discussion (0)

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Reference graph

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