Paper 2026/1095

Key Transport over Untrusted QKD Relay Networks

Antoine Gansel, Universität Regensburg

Patrick Struck, Universität Konstanz

Abstract

Quantum key distribution (QKD) enables the exchange of information-theoretically secure symmetric keys, but is fundamentally limited in range. Existing long-distance QKD networks rely on trusted relay nodes, any one of which can compromise the entire key. We propose a key-transport protocol that removes this trust assumption by combining proactive secret sharing with one-time pad encryption over pairwise QKD links. At each layer of relay nodes, shares are reshared so that corruptions across different layers cannot be combined; security depends only on the maximum number of corruptions within any single layer, not on the total number of corrupted nodes. We formalize a game-based security model for layered secret transport, identify a cross-layer attack that affects a prior construction, and prove our protocol information-theoretically secure against a semi-honest adversary corrupting up to $t{-}1$ nodes per layer.

@misc{cryptoeprint:2026/1095,
      author = {Sebastian Clermont and Antoine Gansel and Patrick Struck},
      title = {Key Transport over Untrusted {QKD} Relay Networks},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/1095},
      year = {2026},
      url = {https://eprint.iacr.org/2026/1095}
}