REVIEW 5 major objections 5 minor 19 references
Malleability of transformations on the ciphertext in noisy Quantum public key encryption
T0 review · 5 major / 5 minor · reviewed 2026-07-31 · deepseek-v4-flash
Pith's one-line read Everlasting security survives noise in quantum encryption
desk verdict The central everlasting-security claim is the definition itself, proved by assuming the conclusion and manipulating undefined ratios of kets; not ready for review. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The argument is carried by two objects. First, the noisy projection operator eΠ, which replaces each pure signature state |σ⟩ in the noiseless projection Π by |σ+noise⟩ (with 'noise' left unspecified), is used to inject noise into the protocol's acceptance check. Second, an adaptation of the Gentle Measurement Lemma from quantum information theory is the mechanism that converts a lower bound on the trace of a ratio of noisy/noiseless state differences—derived through a chain of up-to-constant inequalities with constants C, C′, C′′—into an upper bound of 2√ϵ on the trace distance between hybrid experiments. The negligibility function NEGL(λ′) then absorbs the security threshold gap λ′−λ. Thes
What would settle it
Take any specific, normalized noise model (for instance, a depolarizing channel applied to the signature register) and compute the trace distance Td(gExp_{A_{λ′}}(1^{λ′},1), gExp_{A_{λ′}}(1^{λ′},0)) for a finite security parameter λ′. If the value exceeds the claimed upper bound NEGL(λ′) (or the intermediate lower-bound step Tr ≥ 1−ϵ fails), the theorem is false.
Extended reading notes
Core claim
The paper's central claim is Theorem: if the noisy quantum public-key encryption protocol is correct (decoding never aborts erroneously and always succeeds), then the trace distance between the two noisy experiments, Td(gExp_{A_{λ′}}(1^{λ′},1), gExp_{A_{λ′}}(1^{λ′},0)), is bounded, up to constants, by NEGL(λ′), where λ′ > λ is a higher security threshold. In other words, noisy everlasting security holds in the sense that the real and ideal worlds are indistinguishable even to a computationally unbounded adversary who later receives the quantum secret key. The derivation rests on an adaptation of the Gentle Measurement Lemma: the paper first proves a lower bound on a trace involving ratios of
Load-bearing premise
The load-bearing premise is that the noisy projection operator eΠ—which adds an undefined 'noise' to each signature state without normalization or proof that it is a valid quantum operation—is a legitimate mathematical object; if that operator is not well-defined, the entire noisy protocol and the derived trace-distance bound collapse.
Editorial extensions
If this is right
- If correct, noisy everlasting security holds for a two-message quantum key distribution protocol, meaning the post-quantum guarantee degrades to a higher security threshold rather than disappearing under noise.
- The trace-distance bound Td ≲ NEGL(λ′) with NEGL(λ′) related to exp(λ−λ′) gives an explicit quantitative tradeoff: more noise (larger λ′ gap) costs more resources to maintain the same level of security.
- The three noisy advantage functions Adv(0), Adv(1), Adv(2) are all bounded by NEGL(λ′), so hybrid proofs over noisy experiments continue to work.
- The proof technique—using the Gentle Measurement Lemma to turn a trace lower bound into a trace-distance upper bound—is portable to other noisy cryptographic settings.
- The alternative definition of NEGL(λ′) via strong unforgeability of the noisy one-time signature scheme means that unforgeability and indistinguishability are tied in the noisy setting, as in the noiseless case.
Reading between the lines
- If the noisy projection operator were made concrete—say, with additive noise on the signature register followed by renormalization—the same proof structure would likely yield an explicit NEGL(λ′) in terms of the noise amplitude; this would turn the current up-to-constants claim into a testable quantitative bound.
- The higher security threshold λ′ > λ suggests a resource overhead: to achieve the same level of everlasting security as the noiseless protocol, the noisy protocol must run with a larger security parameter, implying a concrete cost in qubits or rounds that could be optimized.
- The malleability framing (forwarding/deleting/reconstruction error probabilities) borrowed from symmetric encryption suggests a route to proving that noisy everlasting security composes under protocol composition, since those error probabilities are designed to track adversarial transformations of ciphertexts.
- One could test the central claim numerically: instantiate the protocol with a specific noise channel and check whether the trace distance between the noisy experiments stays within the claimed bound; a counterexample for a finite λ′ would falsify the theorem.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper claims to characterize a noisy variant of the Quantum Public Key Encryption (QPKE) protocol introduced by Malavolta and Walter, with the goal of extending everlasting security to noisy channels. To this end it introduces a noisy projection operator eΠ (Section 1.1), noisy versions of QPTs, OTSs, and QPKE protocols (Definitions 32–40), and a Lemma asserting that upper bounds on the trace distance follow from lower bounds on traces via the Gentle Measurement Lemma. The main Theorem concludes Td(gExp^{A_{λ′}}(1^{λ′},1), gExp^{A_{λ′}}(1^{λ′},0)) ≲ NEGL(λ′), i.e. noisy everlasting security with a higher security threshold λ′ > λ. The proof is in Sections 4.1–4.2; a Corollary compares three noisy advantage functions. The paper does not provide machine-checked proofs or reproducible code.
Significance. If the main theorem were established, it would be a meaningful extension of the Malavolta–Walter noiseless everlasting-security result to a noisy setting, and it would connect trace-distance bounds to the malleability framework of Maurer–Tackmann. The paper also identifies a plausible technical tool (Gentle Measurement Lemma) for such an extension. However, as written, no such result is actually derived: the theorem's conclusion is identical to Definition37 and is assumed as a premise in the proof; the central Lemma manipulates undefined ratios of kets and operators; and the Gentle Measurement Lemma is applied with the negligibility direction inverted. The claimed theorem is therefore either circular or rests on ill-posed mathematical objects. The potential significance is real, but the manuscript as it stands does not achieve it.
major comments (5)
- [§4.2, Theorem proof] The proof states: 'it suffices to argue that the desired statement holds from the conditions Td(gExp^{A_{λ′}}(1^{λ′},1), gExp^{A_{λ′}}(1^{λ′},0)) ≲ NEGL(λ′) ... which encapsulate everlasting security in the noisy and noiseless settings.' The displayed inequality is exactly the theorem's conclusion and Definition37. Taking it as a 'condition' makes the proof circular. The subsequent chain of implications rewrites the target, and the only non-tautological input, the Lemma, does not independently establish the inequality.
- [§1.1 and Lemma (B.1)–(B.4)] The noisy projection eΠ = Σ_{σ0∈Σ0} |0⟩⊗|σ0+noise⟩⟨σ0+noise|⊗⟨0| + Σ_{σ1∈Σ1} |1⟩⊗|σ1+noise⟩⟨σ1+noise|⊗⟨1| is not a well-defined projector: 'noise' is never specified, |σ+noise⟩ is not normalized, and the summands are not guaranteed orthogonal. The Lemma proof then manipulates ratios such as |c,σc⟩/|ec,fσc⟩, Πρ*Π/(eΠ fρ* eΠ), Tr(Πρ*)/Tr(eΠ fρ*), and |σ0/(σ0+noise)⟩ as if they were scalars or operator quotients. These objects are undefined in Hilbert-space operator formalism, so the estimates (B.1)–(B.4) and the subsequent GML step are not valid mathematical statements.
- [§4.1 Lemma, item (C)] The proof assumes a lower bound of the form 1/2 Tr(...) ≳ 1 − NEGL(λ′−λ)^{-1}. Since NEGL is supposed to be negligible, NEGL(λ′−λ)^{-1} is super-polynomially large, so '1 − NEGL^{-1}' is not close to 1 and may even be negative. The later step 'Td ≤ 2√(NEGL(λ′−λ)^{-1}) ≲ exp(λ−λ′)' is directionally wrong: 2√(NEGL^{-1}) is exponentially large whenever NEGL is exponentially small. The parameter ϵ is effectively chosen after the constants to make the final bound fit, rather than being derived from the GML hypotheses.
- [§3.1, Definitions 37 and 40] Definition37 defines noisy everlasting security as exactly Td(gExp^{A_{λ′}}(1^{λ′},1), gExp^{A_{λ′}}(1^{λ′},0)) ≲ NEGL(λ′). Definition40 defines NEGL(λ′) as the probability of strong unforgeability of the NOTS scheme. The Theorem then uses Definition40 as an 'alternative formulation' of the desired bound, and the Lemma's assumption (C) already contains NEGL(λ′−λ)^{-1}. Thus the main result is a restatement of definitions plus an assumption involving the same negligible function, rather than a derivation of trace-distance security from correctness and unforgeability.
- [§4.1, trace lower bound] The proof of the trace lower bound asserts 1 ≲ Tr(A)/Tr(B) and then '1 ≤ ...', applies Jensen's inequality four times to the square root, introduces constants C, C′, C″ (and repeated C, C′, C″) 'taken sufficiently small', and multiplies by inf_{ρ,τ,eρ,eτ} of a list of traces. No argument shows this infimum is positive, nor that the square-root inequality is valid for operators rather than scalars. These steps are load-bearing because they produce the 1−ϵ lower bound on which the GML invocation depends. Without a valid operator inequality, the constants and the parameter ϵ are free parameters, not derived quantities.
minor comments (5)
- [Definition37] The second random experiment is written gExp^{A_λ}(1^λ,0) instead of gExp^{A_{λ′}}(1^{λ′},0), making the security parameter inconsistent.
- [Lemma, (B.1)–(B.4)] Expressions such as |c_j⟩/|f c_{j′}⟩ appear in sums and tensor products; these are not defined quantum states, and the '≲' relation is never given a precise norm or ordering. This makes the inequalities unverifiable in their current form.
- [Section 3.2] The lengthy 'Run Time' comparisons and subsequentiality assumptions are heuristic and are not formally connected to the Theorem or Corollary. They should either be made precise or removed from the main development.
- [Definitions 34–36 and Theorem proof] The noisy objects (gVer, fvk, esk, ^SKGen, eρ, ect) are introduced without specifying a concrete noise model or CPTP map; the assertion '^SKGen ↔ SKGen⊗noise' in the Theorem proof is a definitional stipulation, not a construction.
- [Definition32 and References [14]–[17]] The cited Lemma3.2.3 from [17] is not stated precisely enough for the reader to verify the CPTP contractivity claim; several self-citations are to unpublished or not-yet-available preprints and should be replaced by citable versions or detailed statements.
Circularity Check
Theorem's proof assumes its own conclusion: the target inequality Td(gExp_Aλ'(1^λ',1), gExp_Aλ'(1^λ',0)) ≲ NEGL(λ') is Definition37 and is listed verbatim among the 'conditions' from which the proof says it follows.
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self definitional
[Definition37; Theorem statement and Proof of Theorem, §4.2]
"namely that it suffices to argue that the desired statement holds from the conditions, Td(gExpAλ′(1λ′,1), gExpAλ′(1λ′,0)) ≲ NEGL(λ′), Td(ExpAλ(1λ,1), ExpAλ(1λ,0)) = negl(λ), which encapsulate everlasting security in the noisy and noiseless settings, respectively."
The first 'condition' is exactly the inequality the Theorem must prove and is exactly Definition37's definition of everlasting security. The proof therefore assumes its own conclusion; the remaining text is a sequence of restatements of the same trace-distance inequality. The correctness and unforgeability assumptions are not used to derive the inequality from more basic data.
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other
[Proof of Theorem, §4.2 implication chain after Lemma application]
"=⇒ {Td(gExpAλ′(1λ′,1) ⊗ ExpAλ(1λ,1), gExpAλ′(1λ′,0) ⊗ ExpAλ(1λ,0)) ≤ NEGL(λ′−λ)} =⇒ {Td(...) ≤ NEGL(λ′)} =⇒ {Td(...) ≲ NEGL(λ′−λ)} =⇒ {Td(...) ≲ NEGL(λ′)}"
This '=⇒' chain moves the same trace-distance inequality between experimentation notations and between the parameters λ′−λ and λ′ without proving any new bound. It terminates at the theorem's conclusion, which was already assumed in the preceding 'conditions' sentence. Thus the central everlasting-security claim reduces to its own statement plus the paper's definitions of NEGL.
full rationale
The main result is circular in the strict sense: Definition37 defines everlasting security as Td(gExp_Aλ′(1^λ′,1), gExp_Aλ′(1^λ′,0)) ≲ NEGL(λ′), and the Theorem claims exactly that inequality, while its proof says the 'desired statement holds from the conditions' that include the same inequality. The surrounding Lemma does not break the circle: its lower-bound assumption already contains (NEGL(λ′−λ))^{-1}, and the GML application gives at best a sqrt-type bound, not the claimed NEGL decay; the proof then overwrites this with the desired inequality via the displayed =⇒ chain. I also note that the noisy projection eΠ is introduced as |σ0+noise⟩ without a definition of 'noise' or normalization; this makes the formal objects ill-posed, but the decisive circularity is the theorem's self-assumption rather than the noise model. There is no load-bearing self-citation here: the author's prior work [14,15,16] is background context, and Malavolta–Walter [3] is an external source. Score 9 because the central theorem is forced by the paper's own definition and proof structure.
Assumptions & free parameters
free parameters (4)
- Constants C, C′, C′′ (and repeated C, C′, C′′) =
"taken sufficiently small"
- Noisy security parameter λ′ =
λ′ > λ, unspecified
- Malleability error probabilities δ̃1(q), δ̃2(q), δ̃3(q) =
unspecified positive functions
- GML parameter ϵ =
chosen after constants
assumptions (6)
- standard math Gentle Measurement Lemma: detection probability ≥1−ϵ implies trace distance ≤2√ϵ
- ad hoc to paper Jensen's inequality can be applied four times to the square root inside traces
- ad hoc to paper There exist C,C′,C′′ sufficiently small such that the constant term is ≥ the inf expression >0
- ad hoc to paper By construction ^SKGen ↔ SKGen⊗noise
- ad hoc to paper NEGL(λ′−λ)^{-1} can appear inside a 1−δ lower bound that is close to 1
- domain assumption Two-universal hashing and collision bounds from [10] carry over unchanged to the noisy setting
invented entities (1)
-
Ad hoc 'noise' added to signature states in eΠ
Cite this review
Pith. "Pith review of Malleability of transformations on the ciphertext in noisy Quantum public key encryption." pith.science (2026). https://pith.science/paper/RAURWFB4
@misc{pith2026260726086,
author = {Pith},
title = {Pith review of: Malleability of transformations on the ciphertext in noisy Quantum public key encryption},
year = {2026},
howpublished = {\url{https://pith.science/paper/RAURWFB4}},
note = {Machine review of arXiv:2607.26086}
}
read the original abstract
We characterize a noisy variant of a Quantum public encryption protocol recently introduced by Malavolta and Walter which demonstrated that the notion of everlasting security can be rigorously formulated for Quantum key distribution after two rounds of interaction between Alice and Bob. To address one possible direction of research that is related to injecting noise in the cryptographic protocol related to Quantum key distribution we formulate arguments for further examining the notion of everlasting security through malleability assumptions on transformations of the ciphertext. Assumptions surrounding malleability were introduced by Maurer and Tackmann for the purposes of comparing how authenticate then encrypt, and encrypt then authenticate, protocols behave through a variety of expressions for the forwarding error, deleting error, and reconstruction probabilities. Such probabilities are put to further use for obtaining connections between the indistinguishability and security threshold for a cryptographic protocol of interests. To further build upon such associations we demonstrate, through an adaptation of the Gentle Measurement Lemma from Quantum information theory, how upper bounds on the trace distance can be used to generalize the negligibility function obtained by Malavolta and Walter in the noiseless setting. Besides the fact that the negligibility function in the noisy setting is related to a higher security threshold it continues to remain of interest to determine whether computations provided in this work for upper bounding the trace distance can be related to other settings that are centered more on game-theoretic approaches.
Reference graph
Works this paper leans on
-
[1]
Security and Cryptography for Net- works (SCN), Lecture Notes in Computer Science, Springer9841: pp
Camenisch, J., Enderlein, R.R., Maurer, U. Security and Cryptography for Net- works (SCN), Lecture Notes in Computer Science, Springer9841: pp. 104–125, Aug
-
[2]
Demay, G., Gaˇ zi, P., Hirt, M., Maurer, U. (2013). Resource-Restricted Indifferentia- bility. In: Johansson, T., Nguyen, P.Q. (eds) Advances in Cryptology – EUROCRYPT. Lecture Notes in Computer Science, vol 7881 (2013). Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-38348-9 39
-
[3]
Malavolta, G., Walter, M. (2024). Robust Quantum Public-Key Encryption with Applications to Quantum Key Distribution. In: Reyzin, L., Stebila, D. (eds) Advances in Cryptology – CRYPTO 2024. CRYPTO 2024. Lecture Notes in Computer Science, vol 14926. Springer, Cham. https://doi.org/10.1007/978-3-031-68394-7
-
[4]
Small Accessible Quantum Information Does Not Imply Security
Konig, R., Renner, R., Bariska, A., Maurer, U. Small Accessible Quantum Information Does Not Imply Security. Phys. Rev. Lett. 98(14): 140502 (2007). https://link.aps.org/doi/10.1103/PhysRevLett.98.140502
-
[5]
Direct Product Hardness Amplification
Lanzenberger, D., Maurer, U. Direct Product Hardness Amplification. In: Nissim, K., Waters, B. (eds) Theory of Cryptography. TCC 2021. Lecture Notes in Computer Science, vol 13043 (2021). Springer, Cham. https://doi.org/10.1007/978-3-030-90453-1 21
-
[6]
Confidentiality and Integrity: A Constructive Perspective
Maurer, U., R¨ uedlinger, A., Tackmann, B. Confidentiality and Integrity: A Constructive Perspective. In: Cramer, R. (eds) Theory of Cryptography. TCC. Lec- ture Notes in Computer Science, vol 7194 (2012). Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-28914-9 12
-
[7]
Indistinguishability Amplification
Maurer, U., Pietrzak, K., Renner, R. Indistinguishability Amplification. In: Menezes, A. (eds) Advances in Cryptology - CRYPTO. Lecture Notes in Computer Science, vol 4622 (2007). Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3- 540-74143-5 8
doi:10.1007/978-3- 2007
-
[8]
Indifferentiability, Impossibility Results on Reductions, and Applications to the Random Oracle Methodology
Maurer, U., Renner, R., Holenstein, C. Indifferentiability, Impossibility Results on Reductions, and Applications to the Random Oracle Methodology. Cryptology ePrint Archive, Paper 2003/161 (2003). https://eprint.iacr.org/2003/161. 56
2003
Show all 19 references
-
[9]
On the soundness of authenticate-then-encrypt: formal- izing the malleability of symmetric encryption
Maurer, U., Tackmann, B. On the soundness of authenticate-then-encrypt: formal- izing the malleability of symmetric encryption. In Proceedings of the 17th ACM con- ference on Computer and communications security (2010). Association for Computing Machinery, New York, NY, USA, 5...
2010
-
[10]
QKD parameter estimation by two-universal hashing
Ostrev, D. QKD parameter estimation by two-universal hashing. Quantum7, 894 (2023) https://doi.org/10.22331/q-2023-01-13-894
2023 doi
- [11]
-
[12]
Security of Quantum Key Distribution
Renner, R. Security of Quantum Key Distribution. International Journal of Quan- tum Information 06:01: 1-127 (2008). https://doi.org/10.1142/S0219749908003256
2008 doi
-
[13]
The Exact Price for Unconditionally Secure Asymmet- ric Cryptography
Renner, R., Wolf, S. The Exact Price for Unconditionally Secure Asymmet- ric Cryptography. In: Cachin, C., Camenisch, J.L. (eds) Advances in Cryptology - EUROCRYPT 2004. EUROCRYPT 2004. Lecture Notes in Computer Science,3027. Springer, Berlin, Heidelberg.https://doi.org/10.100...
2004 doi
-
[14]
Probability distributions over CSS codes: two-universality, QKD hashing, collision bounds, security
Rigas, P. Probability distributions over CSS codes: two-universality, QKD hashing, collision bounds, security. arXiv:2510.02402, submitted (2025). https://doi.org/10.48550/arXiv.2510.02402
-
[15]
Eve’s forgery probability from her false acceptance probability: inter- active authentication, Holevo information and the min-entropy
Rigas, P. Eve’s forgery probability from her false acceptance probability: inter- active authentication, Holevo information and the min-entropy. arXiv: 2603.06645, submitted (2026). https://doi.org/10.48550/arXiv.2603.06645
2026 doi
-
[16]
Multiplayer parallel repetition without dependency-breaking and anchor- ing variables: monotonic, concave amplification
Rigas, P. Multiplayer parallel repetition without dependency-breaking and anchor- ing variables: monotonic, concave amplification. arXiv: 2605.08259, submitted (2026). https://doi.org/10.48550/arXiv.2605.08259
-
[17]
Rigas, P. Composable, unconditional security without a Quantum secret key: public broadcast channels and their conceptualizations, adaptive bit transmis- sion rates, fidelity pruning under wiretaps. arXiv:2512.19759, submitted (2026). https://doi.org/10.48550/arXiv.2512.19759
2026 doi
-
[18]
Quantum information theory lecture notes (2015)
Wilde, M. Quantum information theory lecture notes (2015). https://markwilde.com/teaching/2015-fall-qit/lectures/lecture-16.pdf 57
2015
-
[2016]
https://doi.org/10.1007/978-3-319-44618-9 6
Reviewed July 31, 2026 · model on record in the stance chip above.
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