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Reference-beam attacks against twin-field quantum key distribution using optical injection locking

Sergio Juárez1,2,*,†, Alessandro Marcomini3,2,4,*,‡, Mikhail Petrov3,2,4, Robert I. Woodward1, Toby J. Dowling1, R. Mark Stevenson1, Marcos Curty3,2,4, and Davide Rusca3,2,4

  • *These authors contributed equally to this work.
  • †Contact author: sergio.juarez@toshiba.eu
  • ‡Contact author: amarcomini@vqcc.uvigo.es
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Phys. Rev. A 113, 032613 – Published 12 March, 2026

DOI: https://doi.org/10.1103/71m5-3c5n

Abstract

Twin-field quantum key distribution (TF-QKD) has become a leading protocol to bring quantum communications to the national scale. The protocol requires the establishment of a shared phase and frequency reference between distant parties, which is commonly achieved by using an external reference laser in an optical injection locking (OIL) architecture. In this work, we analyze the side channels in OIL-based TF-QKD that may arise from adversarial manipulation of the various degrees of freedom of this untrusted reference beam. We experimentally demonstrate two realistic attack scenarios: fast intensity modulation of the reference laser, and additional signals embedded in the reference light exploiting wavelengths undetectable by conventional monitoring techniques. These attacks can allow a potential eavesdropper to deterministically increase the mean photon number of the sources, or circumvent the decoy-state technique, respectively. To counter these vulnerabilities, we propose practical and highly effective countermeasures that reinforce the security of TF-QKD systems without significant additional complexity or performance degradation.

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References (49)

  1. C. H. Bennett and G. Brassard, Quantum cryptography: Public key distribution and coin tossing, Theor. Comput. Sci. 560, 7 (2014).
  2. A. K. Ekert, Quantum cryptography based on Bell's theorem, Phys. Rev. Lett. 67, 661 (1991).
  3. S. Pirandola, U. L. Andersen, L. Banchi, M. Berta, D. Bunandar, R. Colbeck, D. Englund, T. Gehring, C. Lupo, C. Ottaviani, J. L. Pereira, M. Razavi, J. Shamsul Shaari, M. Tomamichel, V. C. Usenko, G. Vallone, P. Villoresi, and P. Wallden, Advances in quantum cryptography, Adv. Opt. Photon. 12, 1012 (2020).
  4. H.-K. Lo, M. Curty, and K. Tamaki, Secure quantum key distribution, Nat. Photon. 8, 595 (2014).
  5. M. Sasaki, M. Fujiwara, H. Ishizuka, W. Klaus, K. Wakui, M. Takeoka, S. Miki, T. Yamashita, Z. Wang, A. Tanaka, et al., Field test of quantum key distribution in the tokyo QKD network, Opt. Express 19, 10387 (2011).
  6. V. Martin, J. P. Brito, L. Ortíz, R. Méndez, J. Buruaga, R. Vicente, A. Sebastian-Lombrana, D. Rincon, F. Perez, C. Sanchez, et al., MadQCI: a heterogeneous and scalable SDN-QKD network deployed in production facilities, npj Quantum Inf. 10, 80 (2024).
  7. H.-Z. Chen, M.-H. Li, Y. Z. Wang, Z.-G. Zhao, C. Ye, F. L. Li, Z. Chen, S.-L. Han, B. Tang, Y. J. Miao, et al., Implementation of carrier-grade quantum communication networks over 10000 km, npj Quantum Inf. 11, 137 (2025).
  8. M. Lucamarini, Z. L. Yuan, J. F. Dynes, and A. J. Shields, Overcoming the rate-distance limit of quantum key distribution without quantum repeaters, Nat. (London) 557, 400 (2018).
  9. X.-B. Wang, Z.-W. Yu, and X.-L. Hu, Twin-field quantum key distribution with large misalignment error, Phys. Rev. A 98, 062323 (2018).
  10. H. Xu, Z.-W. Yu, C. Jiang, X.-L. Hu, and X.-B. Wang, Sending-or-not-sending twin-field quantum key distribution: Breaking the direct transmission key rate, Phys. Rev. A 101, 042330 (2020).
  11. M. Curty, K. Azuma, and H.-K. Lo, Simple security proof of twin-field type quantum key distribution protocol, npj Quantum Inf. 5, 64 (2019).
  12. M. Curty, T. Moroder, X. Ma, H.-K. Lo, and N. Lütkenhaus, Upper bounds for the secure key rate of the decoy-state quantum key distribution, Phys. Rev. A 79, 032335 (2009).
  13. S. Pirandola, R. Laurenza, C. Ottaviani, and L. Banchi, Fundamental limits of repeaterless quantum communications, Nat. Commun. 8, 15043 (2017).
  14. M. Minder, M. Pittaluga, G. L. Roberts, M. Lucamarini, J. F. Dynes, Z. L. Yuan, and A. J. Shields, Experimental quantum key distribution beyond the repeaterless secret key capacity, Nat. Photon. 13, 334 (2019).
  15. M. Pittaluga, M. Minder, M. Lucamarini, M. Sanzaro, R. I. Woodward, M.-J. Li, Z. Yuan, and A. J. Shields, 600-km repeater-like quantum communications with dual-band stabilization, Nat. Photon. 15, 530 (2021).
  16. J.-P. Chen, C. Zhang, Y. Liu, C. Jiang, D.-F. Zhao, W.-J. Zhang, F.-X. Chen, H. Li, L.-X. You, Z. Wang, Y. Chen, X.-B. Wang, Q. Zhang, and J.-W. Pan, Quantum key distribution over 658 km fiber with distributed vibration sensing, Phys. Rev. Lett. 128, 180502 (2022).
  17. S. Wang, Z.-Q. Yin, D.-Y. He, W. Chen, R.-Q. Wang, P. Ye, Y. Zhou, G.-J. Fan-Yuan, F.-X. Wang, Y.-G. Zhu, P. V. Morozov, A. V. Divochiy, Z. Zhou, G.-C. Guo, and Z.-F. Han, Twin-field quantum key distribution over 830-km fibre, Nat. Photon. 16, 154 (2022).
  18. Y. Liu, W.-J. Zhang, C. Jiang, J.-P. Chen, C. Zhang, W.-X. Pan, D. Ma, H. Dong, J.-M. Xiong, C.-J. Zhang, H. Li, R.-C. Wang, J. Wu, T.-Y. Chen, L. You, X.-B. Wang, Q. Zhang, and J.-W. Pan, Experimental twin-field quantum key distribution over 1000 km fiber distance, Phys. Rev. Lett. 130, 210801 (2023).
  19. M. Pittaluga, Y. S. Lo, A. Brzosko, R. I. Woodward, D. Scalcon, M. S. Winnel, T. Roger, J. F. Dynes, K. A. Owen, S. Juárez, et al., Long-distance coherent quantum communications in deployed telecom networks, Nat. (London) 640, 911 (2025).
  20. J.-P. Chen, C. Zhang, Y. Liu, C. Jiang, W.-J. Zhang, Z.-Y. Han, S.-Z. Ma, X.-L. Hu, Y.-H. Li, H. Liu, F. Zhou, H.-F. Jiang, T.-Y. Chen, H. Li, L.-X. You, Z. Wang, X.-B. Wang, Q. Zhang, and J.-W. Pan, Twin-field quantum key distribution over a 511 km optical fibre linking two distant metropolitan areas, Nat. Photon. 15, 570 (2021).
  21. H. Liu, C. Jiang, H.-T. Zhu, M. Zou, Z.-W. Yu, X.-L. Hu, H. Xu, S. Ma, Z. Han, J.-P. Chen, Y. Dai, S.-B. Tang, W. Zhang, H. Li, L. You, Z. Wang, Y. Hua, H. Hu, H. Zhang, F. Zhou, et al., Field test of twin-field quantum key distribution through sending-or-not-sending over 428 km, Phys. Rev. Lett. 126, 250502 (2021).
  22. C. Clivati, A. Meda, S. Donadello, S. Virzì, M. Genovese, F. Levi, A. Mura, M. Pittaluga, Z. Yuan, A. J. Shields, M. Lucamarini, I. P. Degiovanni, and D. Calonico, Coherent phase transfer for real-world twin-field quantum key distribution, Nat. Commun. 13, 157 (2022).
  23. L. Zhou, J. Lin, Y. Jing, and Z. Yuan, Twin-field quantum key distribution without optical frequency dissemination, Nat. Commun. 14, 928 (2023).
  24. F. Xu, X. Ma, Q. Zhang, H.-K. Lo, and J.-W. Pan, Secure quantum key distribution with realistic devices, Rev. Mod. Phys. 92, 025002 (2020).
  25. V. Zapatero, Á. Navarrete, and M. Curty, Implementation security in quantum key distribution, Adv. Quantum Technol. 8, 2300380 (2025).
  26. N. Jain, B. Stiller, I. Khan, D. Elser, C. Marquardt, and G. Leuchs, Attacks on practical quantum key distribution systems (and how to prevent them), Contemp. Phys. 57, 366 (2016).
  27. V. Makarov, A. Abrikosov, P. Chaiwongkhot, A. K. Fedorov, A. Huang, E. Kiktenko, M. Petrov, A. Ponosova, D. Ruzhitskaya, A. Tayduganov, D. Trefilov, and K. Zaitsev, Preparing a commercial quantum key distribution system for certification against implementation loopholes, Phys. Rev. Appl. 22, 044076 (2024).
  28. Federal Office for Information Security (BSI), Implementation Attacks against QKD Systems, Tech. Rep., Federal Office for Information Security (BSI) (2023), https://www.bsi.bund.de/EN/Service-Navi/Publikationen/Studien/QKD-Systems/Implementation_Attacks_QKD_Systems_node.html.
  29. H.-K. Lo, M. Curty, and B. Qi, Measurement-device-independent quantum key distribution, Phys. Rev. Lett. 108, 130503 (2012).
  30. J. Ye, J.-L. Peng, R. J. Jones, K. W. Holman, J. L. Hall, D. J. Jones, S. A. Diddams, J. Kitching, S. Bize, J. C. Bergquist, L. W. Hollberg, L. Robertsson, and L.-S. Ma, Delivery of high-stability optical and microwave frequency standards over an optical fiber network, J. Opt. Soc. Am. B 20, 1459 (2003).
  31. L. C. Comandar, M. Lucamarini, B. Fröhlich, J. F. Dynes, Z. Yuan, and A. J. Shields, Near perfect mode overlap between independently seeded, gain-switched lasers, Opt. Express 24, 17849 (2016).
  32. T. K. Paraïso, R. I. Woodward, D. G. Marangon, V. Lovic, Z. Yuan, and A. J. Shields, Advanced laser technology for quantum communications (tutorial review), Adv. Quantum Technol. 4, 2100062 (2021).
  33. H. Du, T. K. Paraiso, M. Pittaluga, Y. S. Lo, J. A. Dolphin, and A. J. Shields, Twin-field quantum key distribution with optical injection locking and phase encoding on-chip, Optica 11, 1385 (2024).
  34. Q. Peng, J.-P. Chen, T. Xing, D. Wang, Y. Wang, Y. Liu, and A. Huang, Practical security of twin-field quantum key distribution with optical phase-locked loop under wavelength-switching attack, npj Quantum Inf. 11, 7 (2025).
  35. M. Lucamarini, I. Choi, M. B. Ward, J. F. Dynes, Z. L. Yuan, and A. J. Shields, Practical security bounds against the Trojan-horse attack in quantum key distribution, Phys. Rev. X 5, 031030 (2015).
  36. H.-K. Lo, X. Ma, and K. Chen, Decoy state quantum key distribution, Phys. Rev. Lett. 94, 230504 (2005).
  37. S. Sajeed, I. Radchenko, S. Kaiser, J.-P. Bourgoin, A. Pappa, L. Monat, M. Legré, and V. Makarov, Attacks exploiting deviation of mean photon number in quantum key distribution and coin tossing, Phys. Rev. A 91, 032326 (2015).
  38. A. Huang, A. Navarrete, S.-H. Sun, P. Chaiwongkhot, M. Curty, and V. Makarov, Laser-seeding attack in quantum key distribution, Phys. Rev. Appl. 12, 064043 (2019).
  39. See Supplemental Material at http://link.aps.org/supplemental/10.1103/71m5-3c5n for the slow-integrating power meters measurements against the fast intensity modulation (FIM) attack.
  40. H. Tan, M. Petrov, W. Zhang, L. Han, S.-K. Liao, V. Makarov, F. Xu, and J.-W. Pan, Wide-spectrum security of quantum key distribution, PRX Quantum 6, 040331 (2025).
  41. A. Rogalski, Infrared Detectors, 2nd ed. (CRC Press, Boca Raton, 2011).
  42. C. W. Carr, H. B. Radousky, and S. G. Demos, Wavelength dependence of laser-induced damage: Determining the damage initiation mechanisms, Phys. Rev. Lett. 91, 127402 (2003).
  43. J. C. Palais, Fiber Optic Communications, 5th ed. (Pearson/Prentice Hall, Hoboken, 2005).
  44. G. Currás-Lorenzo, A. Navarrete, J. Núñez-Bon, M. Pereira, and M. Curty, Numerical security analysis for quantum key distribution with partial state characterization, Quantum Sci. Technol. 10, 035031 (2025).
  45. K. Tamaki, M. Curty, and M. Lucamarini, Decoy-state quantum key distribution with a leaky source, New J. Phys. 18, 065008 (2016).
  46. W. Wang, K. Tamaki, and M. Curty, Finite-key security analysis for quantum key distribution with leaky sources, New J. Phys. 20, 083027 (2018).
  47. A. Navarrete and M. Curty, Improved finite-key security analysis of quantum key distribution against trojan-horse attacks, Quantum Sci. Technol. 7, 035021 (2022).
  48. G. Currás-Lorenzo, M. Pereira, G. Kato, M. Curty, and K. Tamaki, Security framework for quantum key distribution with imperfect sources, Optica Quantum 3, 525 (2025).
  49. X. Sixto, Á. Navarrete, M. Pereira, G. Currás-Lorenzo, K. Tamaki, and M. Curty, Quantum key distribution with imperfectly isolated devices, Quantum Sci. Technol. 10, 035034 (2025).

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Phys. Rev. A 113, 032613– Published 12 March, 2026
  • Received 1 September 2025
  • Accepted 6 February 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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