REVIEW 2 major objections 2 minor 17 references
One Discrete Gaussian Sample in $2^{n/2+o(n)}$ Time
T0 review · 2 major / 2 minor · reviewed 2026-08-05 · deepseek-v4-flash
Pith's one-line read This paper proves that one sample from any discrete Gaussian can be drawn in $2^{n/2+o(n)}$ time and space, resolving the ADRS open question and yielding faster exact SVP and close-target CVP.
desk verdict The random-superlattice idea is genuinely good and the main theorem may well be right, but the paper leans on an ADRS running-time import I cannot square with the authors' own abstract, and the application constants have a real numerical inconsistency. 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 load-bearing object is a random superlattice obtained by dual sparsification: choose a uniformly random primitive vector $z\in(\mathbb{Z}/2^m\mathbb{Z})^n$, let $M_z$ be the kernel of $a\mapsto\langle z,a\rangle\bmod 2^m$ on $L^*$, and set $L_z=M_z^*\supseteq L$, a superlattice of index $2^m$. This sparsifies the dual lattice, making $L_z$ smooth at $t=s/\sqrt{2}$ with probability at least $3/4$. The Gaussian-mass estimate $\rho_{\sqrt{2}t}(L_z)\le 40(2m^*-1)2^{n/2}\rho_t(L)$ then converts smoothness into a rejection bound: a sample from $D_{L_z,\sqrt{2}t}$ lands in $L$ with inverse-polynomial probability, so the $N=2^{n/2}$ samples from one ADRS call contain a point of $L$ often enough.
What would settle it
On a small lattice (say rank 2 or 3) with a rational basis, run an exact implementation of the ADRS sampler at a parameter $s$ below $\sqrt{2}\,\eta_{1/2}(L)$, record the list length $M$ and the first returned vector in $L$, and test the joint law against the product of the marginals; any detectable dependence of the first $L$-point on $M$ refutes the independence premise behind Lemma 4.1 and would make Algorithm 2's output deviate from $D_{L,s}$.
Extended reading notes
Core claim
Theorem 4.3 is the central claim: given a rational basis of a rank-$n$ lattice $L$ and any rational $s^2>0$, Algorithm 2 outputs a vector $\exp(-\Omega(n^3))$-close to $D_{L,s}$ in expected $2^{n/2+o(n)}$ time and $2^{n/2+o(n)}$ space. The construction samples a random superlattice $L_z$ that is smooth at $t=s/\sqrt{2}$ with constant probability, runs the ADRS sampler on $L_z$ at $\sqrt{2}t$, and returns the first returned vector that lies in $L$. The sampler's list length is independent of the sample values, so conditioning gives exactly $D_{L,s}$. A Gaussian-mass comparison, tight in its $2^{n/2}$ factor, shows the list catches $L$ with inverse-polynomial probability; the same comparison,
Load-bearing premise
The construction rests on the imported guarantee that the ADRS sampler's list length $M$ is chosen independently of the sampled vectors even below the smoothing threshold; if $M$ and the sample values were correlated, the first vector in $L$ would not be distributed as $D_{L,s}$.
Editorial extensions
If this is right
- One sample from $D_{L,s}$ can be drawn at every rational scale in time $2^{n/2+o(n)}$ with error $\exp(-\Omega(n^3))$, resolving the ADRS open question.
- The factor $2^{n/2}$ in the mass comparison is tight, so the running-time improvement is not an artifact of a loose comparison.
- Exact CVP on targets within $\alpha\lambda_1(L)$ for any fixed rational $\alpha<1.4697$ is sub-$2^n$ without a uniqueness assumption; at $\alpha=1$ the exponent is about $0.7315$.
- Exact SVP runs in time $2^{0.7315n+o(n)}$ and space $2^{n/2+o(n)}$.
- Any sampler meeting the ADRS guarantee with $N=2^{\xi n}$ outputs at cost $2^{\omega n}$ per call and $2^{\zeta n}$ space gives exact SVP in time $2^{(\omega+\max\{0,1/2+\delta-\xi\})n}$, where $\delta\approx0.2315$, isolating sampling cost from repetition count.
Reading between the lines
- The superlattice-rejection pattern may transfer to other distributions whose envelope can be smoothed at a slightly smaller scale, provided the sampler's list length stays independent of the values.
- Because the exact-SVP exponent depends on the spherical-code constant through $\delta$, any future improvement to that constant would automatically lower $2^{0.7315n+o(n)}$ within the same framework.
- The paper itself notes two boundaries: it stores one ADRS output list of size $2^{n/2+o(n)}$, and the construction is centered—arbitrary-parameter shifted DGS is not reached because $\rho_s(L-y)/\rho_s(L)$ can be arbitrarily small.
- Tightness of the $2^{n/2}$ comparison suggests this rejection route cannot be pushed below $2^{n/2}$ for one sample; a different mechanism would be needed for a faster one-sample DGS.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper gives an algorithm that, given a rational basis of a full-rank lattice L and a rational squared parameter s^2>0, outputs one vector within statistical distance exp(-Ω(n^3)) of the discrete Gaussian D_{L,s}, in expected 2^{n/2+o(n)} time and 2^{n/2+o(n)} space on every execution. The method embeds L in a random superlattice L_z chosen by dual sparsification, argues that L_z is smooth at t=s/√2 with constant probability, calls the ADRS sampler on L_z at parameter √2t, and returns the first sampled vector that lies in L. A Gaussian-mass comparison gives inverse-polynomial success probability per call. The paper also derives applications to exact CVP for close targets and to exact SVP, claiming sub-2^n CVP for α<1.4697 and SVP in 2^{0.7315n+o(n)} time.
Significance. If correct, Theorem 4.3 resolves the ADRS open question affirmatively: one discrete Gaussian sample at an arbitrary parameter is obtainable at the above-smoothing cost. The core construction is elegant, and the paper is unusually careful about randomized Turing-machine implementation, certified arithmetic, and space bounds on every execution. The tightness statement in Theorem 3.8 is a valuable addition. However, the main time bound relies on an imported ADRS theorem whose statement appears in tension with the paper's own abstract, and Section 6 contains an internal numerical inconsistency in the constants that propagates to the advertised application exponents. These points need to be resolved before the claims can be accepted.
major comments (2)
- [Section 2 (Theorem 2.6) and Section 4 (Algorithm 2, Theorem 4.3)] The running-time assertion of Theorem 2.6, 'running time and space are 2^{n/2+polylog(κ)+o(n)}', is stated without the threshold condition, although Definition 2.5 only forces M=N when s>φ(L). The paper's own abstract says ADRS's arbitrary-parameter sampler costs 2^{n+o(n)} and only the above-smoothing sampler costs 2^{n/2+o(n)}. This distinction is load-bearing: Algorithm 2 loops over all m=1..J (line 6), and for m<m* the superlattice L_z is not guaranteed to be smooth at t, so the calls at s=√2t are below φ(L_z). Under the actual ADRS guarantee those calls would cost 2^{n+o(n)} each, and there are J·T=O(J^2κ0) such calls per iteration, giving 2^{n+o(n)}poly(n,β_s) rather than 2^{n/2+o(n)}. The proof of Theorem 4.3 says 'Each call costs 2^{n/2+o(n)} ... by Theorem 2.6' but does not address the modulus range; Section 5.3 only sums costs per call and absorbs J as a polynomial factor. Plea
- [Section 6, constants before Lemma 6.1] With cLev≈0.4014 and βLev=2cLev≈0.8028, the displayed value μ=βLev^2/(2e ln2) evaluates to ≈0.171, not ≈0.4629. Consequently δ=μ/2 and c0=1/2+δ are ≈0.0855 and ≈0.5855, not 0.2315 and 0.7315. These constants are used in Theorem 6.4 (1/√μ≈1.4697), Theorem 6.6 (c0), Theorem 6.7, and the abstract. The stated exponents and thresholds are therefore internally inconsistent with the definitions. Please correct the constants and re-derive the affected statements.
minor comments (2)
- [Section 5.1, Lemma 5.3] In the statement of Lemma 5.3, H is defined as ⌈2KT(x)⌉, but the proof's Markov step claims an exceedance probability of 2^{-K}. With the written definition, Markov's inequality gives at most 1/(2K). If the intended definition is H=⌈2^K T(x)⌉, please fix the notation; otherwise the cutoff error is only inverse-polynomial, not exp(-Ω(K)).
- [Section 1 and Section 2] The description of the ADRS result in the introduction ('arbitrary parameter in 2^{n+o(n)}; above smoothing in 2^{n/2+o(n)}') should be stated in the same terms as Theorem 2.6, since the current discrepancy is the source of the main technical concern above.
Circularity Check
No significant circularity: the derivation is self-contained given the external ADRS sampler and standard Poisson/Gaussian-mass facts.
full rationale
The paper's central algorithm samples from a randomly sparsified superlattice L_z that is smooth at t=s/√2, invokes the ADRS sampler at √2t (above L_z's smoothing threshold), and filters out points not in L. The acceptance probability is bounded by Theorem 3.4 via Poisson summation and dual-mass estimates; no parameter is fitted to the target D_{L,s} distribution. The modulus m* and repetition counts J,T are explicit functions of the input and of rational upper bounds on Θ_t, derived rather than calibrated. Theorem 2.6 is imported from ADRS15 as an external published sampler guarantee, not a self-citation, and the paper does not redefine or rename it; if that guarantee is misstated, the honest criticism is a correctness/soundness one, not constructional circularity. Theorems 3.7–3.8 give a genuine unconditional lower bound on the mass comparison, not a circular use of the upper bound. Section 7's stated limitations (storing one 2^{n/2}-size list; centered, non-shifted DGS) are acknowledged constraints, not hidden circular inputs. Under the review rules, none of the derivation steps reduces to its own inputs, so the circularity score is 0.
Assumptions & free parameters
assumptions (4)
- domain assumption ADRS sampler guarantee (Definition 2.5 and Theorem 2.6): a 2^(n/2+o(n))-time sampler that outputs N samples above the threshold sqrt(2)*eta_{1/2}(L), and a random number M of samples below it, with M independent of the sample values.
- standard math Poisson summation identity rho_s(L) = s^n/det(L) * rho_{1/s}(L^*)
- domain assumption Kabatiansky-Levenshtein spherical-code bound and the effective Gaussian mass bound in Lemma 6.1
- domain assumption Lattice sparsification by a random kernel from Danush-Kun (DK16), summarized in Lemma 3.1 and 3.2
Cite this review
Pith. "Pith review of One Discrete Gaussian Sample in $2^{n/2+o(n)}$ Time." pith.science (2026). https://pith.science/paper/ZCWOIHFJ
@misc{pith2026260803220,
author = {Pith},
title = {Pith review of: One Discrete Gaussian Sample in $2^n/2+o(n)$ Time},
year = {2026},
howpublished = {\url{https://pith.science/paper/ZCWOIHFJ}},
note = {Machine review of arXiv:2608.03220}
}
abstract
Aggarwal, Dadush, Regev, and Stephens-Davidowitz (ADRS; STOC 2015) sample $2^{n/2}$ discrete Gaussians at an arbitrary parameter in $2^{n+o(n)}$ time, and above smoothing in $2^{n/2+o(n)}$ time. They ask whether the latter bound suffices for one sample at an arbitrary parameter. We answer this question affirmatively: for every rank-$n$ lattice $L\subseteq\R^n$ specified by a rational basis and every rational $s^2>0$, we produce one sample from $D_{L,s}$ within statistical distance $\exp(-\Omega(n^3))$ in expected $2^{n/2+o(n)}$ time and $2^{n/2+o(n)}$ space on every execution. The algorithm samples from random superlattices that are smooth at the required scale with constant probability and outputs the first point in $L$; a Gaussian-mass comparison shows that the $2^{n/2}$ samples produced by one ADRS call contain a point of $L$ with inverse-polynomial probability. The factor $2^{n/2}$ is tight in this Gaussian-mass comparison. For every fixed rational $\alpha<1.4697$, the same comparison gives a sub-$2^n$ algorithm for exact CVP on targets satisfying $\dist(y,L)\le\alpha\lambda_1(L)$, without a uniqueness assumption, and an exact-SVP algorithm in $2^{0.7315n+o(n)}$ time.
Reference graph
Works this paper leans on
-
[1]
Fine- grained hardness of CVP(P) – everything that we can prove (and nothing else)
[ABGS21] Divesh Aggarwal, Huck Bennett, Alexander Golovnev, and Noah Stephens-Davidowitz. Fine- grained hardness of CVP(P) – everything that we can prove (and nothing else). InProceedings of the 2021 ACM-SIAM Symposium on Discrete Algorithms, pages 1816–1835,
work page 2021
-
[4]
doi:10.1109/FOCS.2015
-
[5]
doi:10.1137/1.9781611978315
-
[10]
[DRS14] Daniel Dadush, Oded Regev, and Noah Stephens-Davidowitz
doi: 10.4086/toc.2016.v012a002. [DRS14] Daniel Dadush, Oded Regev, and Noah Stephens-Davidowitz. On the closest vector problem with a distance guarantee. InProceedings of the 29th Annual IEEE Conference on Computational Complexity, pages 98–109, 2014.doi:10.1109/CCC.2014.18. [EWY23] Thomas Espitau, Alexandre Wallet, and Yang Yu. On gaussian sampling, smoo...
-
[12]
26 [GPV08] Craig Gentry, Chris Peikert, and Vinod Vaikuntanathan
URL:https://eprint.iacr.org/2026/1587. 26 [GPV08] Craig Gentry, Chris Peikert, and Vinod Vaikuntanathan. Trapdoors for hard lattices and new cryptographic constructions. InProceedings of the 40th Annual ACM Symposium on Theory of Computing, pages 197–206, 2008.doi:10.1145/1374376.1374407. [Hha26] Minki Hhan. Solving the shortest vector problem in 2 0.6039...
arXiv 2026
-
[13]
Solving the Shortest Vector Problem in $2^{0.6039n}$ Time via Mid-point Hessian
URL:https://arxiv.org/abs/2608.02478,arXiv:2608.02478. [Kar16] Charles F. F. Karney. Sampling exactly from the normal distribution.ACM Transactions on Mathematical Software, 42(1):3:1–3:14, 2016.doi:10.1145/2710016. [KL78] G. A. Kabatiansky and V. I. Levenshtein. Bounds for packings on a sphere and in space. Problemy Peredachi Informatsii, 14(1):3–25,
work page Pith review arXiv 2016
-
[39]
Just take the average! an embarrassingly simple 2 n-time algorithm for SVP (and CVP)
[AS18] Divesh Aggarwal and Noah Stephens-Davidowitz. Just take the average! an embarrassingly simple 2 n-time algorithm for SVP (and CVP). In1st Symposium on Simplicity in Algorithms (SOSA 2018), volume 61 ofOpen Access Series in Informatics, pages 12:1–12:19. Schloss Dagstuhl– Leibniz-Zentrum f¨ ur Informatik, 2018.doi:10.4230/OASIcs.SOSA.2018.12. [BLP+1...
-
[2007]
[MV13] Daniele Micciancio and Panagiotis Voulgaris
doi:10.1137/S0097539705447360. [MV13] Daniele Micciancio and Panagiotis Voulgaris. A deterministic single exponential time algorithm for most lattice problems based on Voronoi cell computations.SIAM Journal on Computing, 42(3):1364–1391, 2013.doi:10.1137/100811970. [Nik20] Geno Nikolov. On the extreme zeros of Jacobi polynomials,
Show all 17 references
-
[2009]
[PS26] Amaury Pouly and Yixin Shen
URL: https://eprint.iacr.org/2009/605. [PS26] Amaury Pouly and Yixin Shen. Solving the shortest vector problem in 2 0.63269n+o(n) time on random lattices. InAdvances in Cryptology – EUROCRYPT 2026, Part IV, pages 92–123. Springer, 2026.doi:10.1007/978-3-032-25327-9_4. [Ste16] ...
2009 doi
-
[2013]
[CCL18] Yanlin Chen, Kai-Min Chung, and Ching-Yi Lai
Statement numbers cited in the text follow the full version, arXiv:1306.0281.doi:10.1145/2488608.2488680. [CCL18] Yanlin Chen, Kai-Min Chung, and Ching-Yi Lai. Space-efficient classical and quantum algorithms for the shortest vector problem.Quantum Information and Computation,...
-
[2015]
[ADS15] Divesh Aggarwal, Daniel Dadush, and Noah Stephens-Davidowitz
Statement numbers cited in the text follow the full version, arXiv:1412.7994.doi:10.1145/2746539.2746606. [ADS15] Divesh Aggarwal, Daniel Dadush, and Noah Stephens-Davidowitz. Solving the closest vector problem in 2 n time – the discrete Gaussian strikes again! InProceedings o...
-
[2016]
[SZ24] Naser Talebizadeh Sardari and Masoud Zargar
doi:10.1137/1.9781611974331.ch121. [SZ24] Naser Talebizadeh Sardari and Masoud Zargar. New upper bounds for spherical codes and packings.Mathematische Annalen, 389:3653–3703, 2024.doi:10.1007/s00208-023-02738-z. A An effective Gaussian-mass bound This appendix makes the o(n) t...
2024 doi
-
[2018]
[CDLP13] Kai-Min Chung, Daniel Dadush, Feng-Hao Liu, and Chris Peikert
doi:10.26421/QIC18.3-4-7. [CDLP13] Kai-Min Chung, Daniel Dadush, Feng-Hao Liu, and Chris Peikert. On the lattice smoothing parameter problem. InProceedings of the 28th IEEE Conference on Computational Complexity, pages 230–241, 2013.doi:10.1109/CCC.2013.31. [CSS26] Cl´ emence ...
2013 doi
-
[2020]
[PS09] Xavier Pujol and Damien Stehl´ e
URL: https://arxiv.org/ abs/2002.02633,arXiv:2002.02633. [PS09] Xavier Pujol and Damien Stehl´ e. Solving the shortest lattice vector problem in time 2 2.465n. Cryptology ePrint Archive, Report 2009/605,
2002 arXiv
-
[2023]
[GFH26] Yiming Gao, Yansong Feng, and Honggang Hu
doi:10.1007/978-981-99-8739-9_3 . [GFH26] Yiming Gao, Yansong Feng, and Honggang Hu. Solving the shortest vector problem in 20.7314n+o(n) time via discrete Gaussian sampling on superlattices. Cryptology ePrint Archive, Report 2026/1587,
2026 doi
-
[2025]
[ADRS15] Divesh Aggarwal, Daniel Dadush, Oded Regev, and Noah Stephens-Davidowitz
Statement numbers cited in the text follow the full version, arXiv:2002.07955.doi:10.1137/22M1486959. [ADRS15] Divesh Aggarwal, Daniel Dadush, Oded Regev, and Noah Stephens-Davidowitz. Solving the shortest vector problem in 2 n time using discrete Gaussian sampling. InProceedi...
2002 arXiv
-
[2026]
[DK16] Daniel Dadush and G´ abor Kun
URL:https://arxiv.org/abs/2605.20133,arXiv:2605.20133. [DK16] Daniel Dadush and G´ abor Kun. Lattice sparsification and the approximate closest vector problem.Theory of Computing, 12(2):1–34,
Reviewed August 5, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.