Effective discrete-modulated continuous variable QKD under general attacks
Pith reviewed 2026-06-26 17:11 UTC · model grok-4.3
The pith
A finite-size security analysis for discrete-modulated CV-QKD produces positive key rates at block sizes of order 10^8 under general attacks.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The authors show that a finite-size security analysis for discrete-modulated continuous variable quantum key distribution protocols, combining the dimension reduction technique with a proof based on marginal-constrained entropy accumulation and a trusted detector model, removes prior restrictions on coherent-state dimensions and achieves positive key rates for relevant block sizes of order 10^8 under general attacks.
What carries the argument
Dimension reduction combined with marginal-constrained entropy accumulation under a trusted detector model for receiver imperfections.
If this is right
- Positive secret key rates become available for discrete-modulated CV-QKD at block sizes of order 10^8 against general attacks.
- No bounded-dimension assumption on coherent states is needed to prove security.
- Receiver imperfections can be incorporated realistically while preserving usable finite-size rates.
- Standard telecom components and simplified postprocessing suffice for the protocol.
Where Pith is reading between the lines
- The same combination of techniques might extend to other discrete modulation formats or channel models without re-deriving the full proof.
- If detector trust cannot be maintained, the key-rate claims would require a separate analysis of untrusted components.
- Experimental implementations at 10^8 blocks could directly test whether the modeled rates match observed performance.
Load-bearing premise
The analysis assumes a trusted detector whose imperfections are accurately modeled and fully accounted for in the security proof.
What would settle it
An experiment or calculation demonstrating that an eavesdropper can extract more information than the trusted-detector model predicts for block sizes near 10^8 would falsify the reported positive key rates.
Figures
read the original abstract
Continuous variable quantum key distribution via discrete modulations ensures information-theoretic security using standard telecom technologies, providing affordable and scalable quantum communications with simplified classical postprocessing. However, existing security proofs against general attacks often rely on restrictive assumptions, such as a bounded dimension for coherent states, or require impractically large block sizes. In this work, we develop a finite-size security analysis that removes these limitations while incorporating realistic experimental features. Our approach combines the dimension reduction technique, a security proof based on the marginal-constrained entropy accumulation, and a trusted detector model accounting for the receiver imperfections. We report positive key rates in the finite-size regime for relevant block sizes of the order of $10^8$. These results contribute to narrowing the gap between theoretical security proofs and practical implementations of discrete-modulated continuous variable quantum key distribution protocols.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript develops a finite-size security analysis for discrete-modulated continuous-variable quantum key distribution (CV-QKD) under general attacks. It combines the dimension reduction technique, a security proof based on marginal-constrained entropy accumulation, and a trusted detector model that accounts for receiver imperfections. The central claim is that this approach yields positive secret key rates for block sizes on the order of 10^8, removing prior limitations such as bounded coherent-state dimensions or impractically large blocks while incorporating realistic experimental features.
Significance. If the analysis is sound, the result is significant for the field: it narrows the gap between theoretical security proofs and practical DM-CV-QKD implementations that rely on standard telecom components and simplified post-processing. The integration of dimension reduction with entropy accumulation under a trusted-detector assumption enables finite-size rates at experimentally relevant scales, strengthening the case for scalable, information-theoretically secure CV-QKD.
major comments (1)
- The headline claim of positive key rates at block sizes ~10^8 is load-bearing on the trusted detector model fully capturing every receiver imperfection exploitable under general attacks. The abstract states that the model 'accounts for the receiver imperfections,' but without explicit bounds or a section showing that any mismatch between modeled and actual detector behavior leaves the marginal-constrained entropy accumulation bounds intact, the finite-size rates cannot be considered secure.
minor comments (1)
- [Abstract] The abstract refers to 'relevant block sizes of the order of 10^8' without specifying the exact modulation cardinality, channel transmittance, or excess noise values at which positive rates are obtained; a short table or sentence in the introduction would clarify the operating regime.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive comment on our manuscript. We address the major point below.
read point-by-point responses
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Referee: The headline claim of positive key rates at block sizes ~10^8 is load-bearing on the trusted detector model fully capturing every receiver imperfection exploitable under general attacks. The abstract states that the model 'accounts for the receiver imperfections,' but without explicit bounds or a section showing that any mismatch between modeled and actual detector behavior leaves the marginal-constrained entropy accumulation bounds intact, the finite-size rates cannot be considered secure.
Authors: The security proof is derived under the explicit assumption of a trusted detector model in which all relevant receiver imperfections (efficiency, electronic noise, etc.) are fully characterized and folded into the observed marginal statistics that constrain the entropy accumulation. This modeling choice is standard in CV-QKD analyses; the dimension-reduction and marginal-constrained entropy accumulation steps are performed with respect to these modeled statistics. Any physical mismatch between the assumed model and the actual detector would place the implementation outside the scope of the claimed security guarantee, exactly as occurs with trusted-source or trusted-channel assumptions in other proofs. We will add a clarifying paragraph in the security-analysis section stating this assumption explicitly and noting that the reported rates are conditional on the model fidelity. This revision improves transparency without requiring new bounds or altering the core results. revision: yes
Circularity Check
Security analysis combines established techniques (dimension reduction, entropy accumulation, trusted detector) with no reduction of key rates to fitted parameters or self-referential definitions
full rationale
The abstract and description present the finite-size key rate result as arising from a combination of the dimension reduction technique, marginal-constrained entropy accumulation, and a trusted detector model. No equations or steps are shown that define a quantity in terms of itself or rename a fit as a prediction. Any self-citations to prior work on these techniques are not load-bearing in a way that collapses the central claim to a tautology; the reported positive rates at block size ~10^8 rest on the external validity of those methods rather than internal redefinition. This is the normal case of an incremental application of known tools.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Trusted detector model accounts for receiver imperfections
Reference graph
Works this paper leans on
-
[1]
C. H. Bennett and G. Brassard, ‘Quantum Cryptography: Public Key Distribution and Coin Tossing’, in Proceedings of the ieee international conference on computers, systems and signal processing (1984), pp. 175–179
1984
-
[2]
C. H. Bennett, G. Brassard and N. D. Mermin, ‘Quantum cryptography without bell’s the- orem’, Phys. Rev. Lett.68, 557–559 (1992),https : / / link . aps . org / doi / 10 . 1103 / PhysRevLett.68.557
1992
-
[3]
A. K. Ekert, ‘Quantum cryptography based on Bell’s theorem’, Physical review letters67, 661–663 (1991)
1991
-
[4]
Renner, ‘Security of quantum key distribution’, PhD thesis (Swiss Federal Institute of Technology, 2006), eprint:ArXiv:0512258[quant-ph]
R. Renner, ‘Security of quantum key distribution’, PhD thesis (Swiss Federal Institute of Technology, 2006), eprint:ArXiv:0512258[quant-ph]
2006
-
[5]
C. Portmann and R. Renner, ‘Security in quantum cryptography’, Rev. Mod. Phys.94, 025008 (2022),https://link.aps.org/doi/10.1103/RevModPhys.94.025008
-
[6]
Diamanti and A
E. Diamanti and A. Leverrier, ‘Distributing secret keys with quantum continuous variables: principle, security and implementations’, Entropy17, 6072–6092 (2015),https : / / www . mdpi.com/1099-4300/17/9/6072
2015
-
[7]
Pirandola, U
S. Pirandola, U. L. Andersen, L. Banchi, M. Berta, D. Bunandar, R. Colbeck, D. Englund, T. Gehring, C. Lupo, C. Ottaviani et al., ‘Advances in quantum cryptography’, Advances in optics and photonics12, 1012–1236 (2020)
2020
-
[8]
Y. Zhang, Y. Bian, Z. Li, S. Yu and H. Guo, ‘Continuous-variable quantum key distribution system: Past, present, and future’, Applied Physics Reviews11, 011318 (2024),https : //doi.org/10.1063/5.0179566
-
[9]
M. F. Anka, J. A. Mora Rodríguez, D. F. Pinto, L. Q. Galvão, M. A. Dias and A. B. Tacla, ‘An introductory review of the theory of continuous-variable quantum key distribution: fundamentals, protocols, and security’, Brazilian Journal of Physics56,doi: 10.1007/s13538- 025-01975-8 (2026),http://dx.doi.org/10.1007/s13538-025-01975-8
-
[10]
Grosshans and P
F. Grosshans and P. Grangier, ‘Continuous variable quantum cryptography using coherent states’, Physical Review Letters88, 057902 (2002)
2002
-
[11]
Grosshans, G
F. Grosshans, G. Van Assche, J. Wenger, R. Brouri, N. J. Cerf and P. Grangier, ‘Quantum key distribution using gaussian-modulated coherent states’, Nature421, 238–241 (2003), https://www.nature.com/articles/nature01289. 14
2003
-
[12]
L. Mariani, R. Yehia, C. Pascual-García, F. Centrone, J. van der Kolk, M. Ángeles Serrano and A. Acín,Quantum key distribution over complex networks, 2025, arXiv:2504 . 02372 [quant-ph],https://arxiv.org/abs/2504.02372
arXiv 2025
-
[13]
Leverrier, ‘Theoretical study of continuous-variable quantum key distribution’, PhD thesis (Telecom ParisTech, 2009)
A. Leverrier, ‘Theoretical study of continuous-variable quantum key distribution’, PhD thesis (Telecom ParisTech, 2009)
2009
-
[14]
A. Leverrier and P. Grangier, ‘Unconditional security proof of long-distance continuous- variable quantum key distribution with discrete modulation’, Phys. Rev. Lett.102, 180504 (2009),https://link.aps.org/doi/10.1103/PhysRevLett.102.180504
-
[15]
S. Ghorai, P. Grangier, E. Diamanti and A. Leverrier, ‘Asymptotic security of continuous- variable quantum key distribution with a discrete modulation’, Phys. Rev. X9, 021059 (2019),https://link.aps.org/doi/10.1103/PhysRevX.9.021059
-
[16]
F. Roumestan, A. Ghazisaeidi, J. Renaudier, L. T. Vidarte, A. Leverrier, E. Diamanti and P. Grangier, ‘Shaped constellation continuous variable quantum key distribution: con- cepts, methods and experimental validation’, Journal of Lightwave Technology42, 5182–5189 (2024),http://dx.doi.org/10.1109/JLT.2024.3391168
-
[17]
S.Bäuml,C.Pascual-García,V.Wright,O.FawziandA.Acín,‘Securityofdiscrete-modulated continuous-variable quantum key distribution’, Quantum8, 1418 (2024),https://doi.org/ 10.22331/q-2024-07-18-1418
-
[18]
C. Pascual-García, S. Bäuml, M. Araújo, R. Liss and A. Acín, ‘Improved finite-size key rates fordiscrete-modulatedcontinuous-variablequantumkeydistributionundercoherentattacks’, Phys. Rev. A111, 022610 (2025),https://link.aps.org/doi/10.1103/PhysRevA.111. 022610
-
[19]
I. W. Primaatmaja, W. Y. Kon and C. Lim,Discrete-modulated continuous-variable quantum key distribution secure against general attacks, 2024, arXiv:2409.02630 [quant-ph],https: //arxiv.org/abs/2409.02630
arXiv 2024
-
[20]
M. Navarro, A. G. Lorente, P. V. Parellada, C. Pascual-García and M. Araújo,Finite-size quantum key distribution rates from rényi entropies using conic optimization, 2026, arXiv:2 511.10584 [quant-ph],https://arxiv.org/abs/2511.10584
Pith/arXiv arXiv 2026
-
[21]
J.Lin,T.UpadhyayaandN.Lütkenhaus,‘Asymptoticsecurityanalysisofdiscrete-modulated continuous-variable quantum key distribution’, Phys. Rev. X9, 041064 (2019),https:// link.aps.org/doi/10.1103/PhysRevX.9.041064
-
[22]
T.Upadhyaya,T.vanHimbeeck,J.LinandN.Lütkenhaus,‘Dimensionreductioninquantum key distribution for continuous- and discrete-variable protocols’, PRX Quantum2, 020325 (2021),https://link.aps.org/doi/10.1103/PRXQuantum.2.020325
-
[23]
Dupuis, O
F. Dupuis, O. Fawzi and R. Renner, ‘Entropy accumulation’, Communications in Mathem- atical Physics379, 867–913 (2020)
2020
-
[24]
Dupuis and O
F. Dupuis and O. Fawzi, ‘Entropy accumulation with improved second-order term’, IEEE Transactions on information theory65, 7596–7612 (2019)
2019
-
[25]
Metger and R
T. Metger and R. Renner, ‘Security of quantum key distribution from generalised entropy accumulation’, Nature Communications14, 5272 (2023),https://www.nature.com/artic les/s41467-023-40920-8
2023
-
[26]
A. Arqand and E. Y. Z. Tan,Marginal-constrained entropy accumulation theorem, 2025, arXiv:2502.02563 [quant-ph]
arXiv 2025
-
[27]
Dupuis, ‘Privacy amplification and decoupling without smoothing’, IEEE Transactions on Information Theory69, 7784–7792 (2023)
F. Dupuis, ‘Privacy amplification and decoupling without smoothing’, IEEE Transactions on Information Theory69, 7784–7792 (2023)
2023
- [28]
-
[29]
Skajaa and Y
A. Skajaa and Y. Ye, ‘A homogeneous interior-point algorithm for nonsymmetric convex conic optimization’, Mathematical Programming150, 391–422 (2015)
2015
-
[30]
A homogeneous interior-point algorithm for non-symmetric con- vex conic optimization
D. Papp and S. Yıldız,On “A homogeneous interior-point algorithm for non-symmetric con- vex conic optimization”, 2017, arXiv:1712.00492 [math.OC]. 15
Pith/arXiv arXiv 2017
-
[31]
A. G. Lorente, P. V. Parellada, M. Castillo-Celeita and M. Araújo,Quantum key distribution rates from non-symmetric conic optimization, 2024, arXiv:2407.00152 [quant-ph],https: //arxiv.org/abs/2407.00152
arXiv 2024
-
[32]
D. Drusvyatskiy and H. Wolkowicz, ‘The many faces of degeneracy in conic optimization’, Foundations and Trends in Optimization3, 77–170 (2017), arXiv:1706.03705 [quant-ph]
Pith/arXiv arXiv 2017
-
[33]
H. Hu, J. Im, J. Lin, N. Lütkenhaus and H. Wolkowicz, ‘Robust interior point method for quantum key distribution rate computation’, Quantum6, 792 (2022). [34]ConicQKD.jl: Implementation of convex cones for quantum key distribution.2025,https: //github.com/araujoms/ConicQKD.jl. [35]Renyi-ConicQKD, 2025,https://github.com/MarianaNvrr/Renyi-ConicQKD
2022
-
[34]
F. Kanitschar and C. Pacher, ‘Optimizing continuous-variable quantum key distribution with phase-shift keying modulation and postselection’, Phys. Rev. Appl.18, 034073 (2022),http s://link.aps.org/doi/10.1103/PhysRevApplied.18.034073
-
[35]
J. Lin and N. Lütkenhaus, ‘Trusted detector noise analysis for discrete modulation schemes of continuous-variable quantum key distribution’, Phys. Rev. Appl.14, 064030 (2020),https: //link.aps.org/doi/10.1103/PhysRevApplied.14.064030
-
[36]
F. Kanitschar, I. George, J. Lin, T. Upadhyaya and N. Lütkenhaus, ‘Finite-size security for discrete-modulated continuous-variable quantum key distribution protocols’, PRX Quantum 4, 040306 (2023),https://link.aps.org/doi/10.1103/PRXQuantum.4.040306
-
[37]
C. Ferradini, M. Sandfuchs, R. Wolf and R. Renner,Defining security in quantum key dis- tribution, 2025, arXiv:2509.13405 [quant-ph],https://arxiv.org/abs/2509.13405
arXiv 2025
-
[38]
W. Hoeffding, ‘Probability inequalities for sums of bounded random variables’, Journal of the American Statistical Association58, 13–30 (1963),https://www.tandfonline.com/ doi/abs/10.1080/01621459.1963.10500830
-
[39]
G. Staffieri, G. Scala and C. Lupo,Finite-size secret-key rates of discrete modulation cv qkd under passive attacks, 2025, eprint:2509 . 14345(quant-ph),https : / / arxiv . org / abs / 2509.14345
arXiv 2025
-
[40]
A. Marwah and F. Dupuis, ‘Uniform continuity bound for sandwiched rényi conditional entropy’, Journal of Mathematical Physics63,doi: 10.1063/5.0088507 (2022),http://dx. doi.org/10.1063/5.0088507
-
[41]
A. Bluhm, A. Capel, P. Gondolf and T. Möbus, ‘Unified framework for continuity of sand- wiched rényi divergences’, Annales Henri Poincaré,doi: 10.1007/s00023-024-01519-x (2024), http://dx.doi.org/10.1007/s00023-024-01519-x
-
[42]
Slepian and J
D. Slepian and J. Wolf, ‘Noiseless coding of correlated information sources’, IEEE Transac- tions on Information Theory19, 471–480 (1973)
1973
-
[43]
Boyd and L
S. Boyd and L. Vandenberghe,Convex optimization(Cambridge University Press, 2004)
2004
-
[44]
Nesterov,Lectures on convex optimization(Springer, 2018)
Y. Nesterov,Lectures on convex optimization(Springer, 2018)
2018
-
[45]
A. A. E. Hajomer, F. Kanitschar, N. Jain, M. Hentschel, R. Zhang, N. Lütkenhaus, U. L. An- dersen, C. Pacher and T. Gehring, ‘Experimental composable key distribution using discrete- modulated continuous variable quantum cryptography’, Light: Science & Applications14, 255 (2025),https://doi.org/10.1038/s41377-025-01924-9
-
[46]
C. Coey, L. Kapelevich and J. P. Vielma, ‘Performance enhancements for a generic conic in- terior point algorithm’, Mathematical Programming Computation15, 53–101 (2023), arXiv:2 107.04262 [math.OC]
2023
-
[47]
D. Tupkary, E. Y.-Z. Tan and N. Lütkenhaus, ‘Security proof for variable-length quantum key distribution’, Phys. Rev. Res.6, 023002 (2024), arXiv:2311.01600 [quant-ph]
arXiv 2024
-
[48]
F. Kanitschar and M. Huber, ‘Composable finite-size security of high-dimensional quantum- key-distribution protocols’, Phys. Rev. Appl.24, 054028 (2025),https://link.aps.org/ doi/10.1103/v51y-vkfr. 16
-
[49]
D. Tupkary, S. Nahar, A. Arqand, E. Y. Z. Tan and N. Lütkenhaus,A rigorous and com- plete security proof of decoy-state bb84 quantum key distribution, 2026, arXiv:2601.18035 [quant-ph],https://arxiv.org/abs/2601.18035
arXiv 2026
-
[50]
A. Mizutani, T. Sasaki and G. Kato,Protocol-level description and self-contained security proof of decoy-state bb84 qkd protocol,2025,arXiv:2504.20417 [quant-ph],https://arxiv. org/abs/2504.20417
arXiv 2025
-
[51]
D. Tupkary, E. Y. Z. Tan, S. Nahar, L. Kamin and N. Lütkenhaus,Qkd security proofs for decoy-state bb84: protocol variations, proof techniques, gaps and limitations, 2025, arXiv:25 02.10340 [quant-ph],https://arxiv.org/abs/2502.10340
Pith/arXiv arXiv 2025
-
[52]
Tomamichel,Quantum information processing with finite resources(Springer Interna- tional Publishing, 2016)
M. Tomamichel,Quantum information processing with finite resources(Springer Interna- tional Publishing, 2016)
2016
-
[53]
Berta, F
M. Berta, F. Furrer and V. B. Scholz, ‘The smooth entropy formalism for von neumann algebras’, Journal of Mathematical Physics57(2016)
2016
-
[54]
Winter, ‘Coding theorem and strong converse for quantum channels’, IEEE Transactions on Information Theory45, 2481–2485 (1999)
A. Winter, ‘Coding theorem and strong converse for quantum channels’, IEEE Transactions on Information Theory45, 2481–2485 (1999)
1999
-
[55]
R.RennerandJ.I.Cirac,‘Definettirepresentationtheoremforinfinite-dimensionalquantum systems and applications to quantum cryptography’, Phys. Rev. Lett.102, 110504 (2009), https://link.aps.org/doi/10.1103/PhysRevLett.102.110504
-
[56]
C. Coey, L. Kapelevich and J. P. Vielma, ‘Solving natural conic formulations with Hypatia.jl’, INFORMS Journal on Computing34, 2686–2699 (2022)
2022
-
[57]
S. Nahar, D. Tupkary, Y. Zhao, N. Lütkenhaus and E. Y.-Z. Tan, ‘Postselection technique for optical quantum key distribution with improved de finetti reductions’, PRX Quantum5, 040315 (2024),https://link.aps.org/doi/10.1103/PRXQuantum.5.040315. 17 A Privacy amplification via Rényi leftover hashing As a starting point in our finite-size analysis, we make u...
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