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arxiv: 2604.01451 · v2 · submitted 2026-04-01 · 💻 cs.CC

Recognition: 2 theorem links

· Lean Theorem

Deterministic Hardness of Approximation For SVP in all Finite ell_p Norms

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Pith reviewed 2026-05-13 21:11 UTC · model grok-4.3

classification 💻 cs.CC
keywords shortest vector problemlattice approximationdeterministic reductionhardness of approximationl_p normsNP-hardnesscomputational complexity
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The pith

Assuming NP lacks subexponential algorithms, approximating the shortest vector in lattices is hard to within 2^{(log n)^{1-o(1)}} in every finite l_p norm via deterministic reduction.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper proves that, under the assumption NP is not contained in subexponential time classes, the shortest vector problem in rank-n lattices is NP-hard to approximate within a factor of 2 raised to nearly log n, for every finite p-norm. The proof constructs a deterministic polynomial-time reduction that maps instances of an NP-complete problem into lattices whose shortest vectors encode the answer. A sympathetic reader cares because this hardness holds uniformly across all norms and without randomness in the reduction, strengthening the case that lattice problems resist efficient approximation. Earlier results left open whether deterministic reductions could achieve comparable factors, especially outside the Euclidean norm.

Core claim

Under the assumption that NP is not contained in the intersection over delta greater than zero of DTIME of exp n to the delta, there is a deterministic reduction establishing that approximating the shortest vector to within 2 to the power of (log n) to the (1 minus o(1)) is hard for lattices of rank n in any finite l_p norm.

What carries the argument

A deterministic reduction from an NP-complete problem that produces lattices whose shortest-vector gap encodes the original instance, with the gap preserved under any chosen finite l_p norm.

If this is right

  • Approximating shortest vectors remains hard even when the reduction itself must be deterministic and cannot use randomness.
  • The same superpolynomial hardness factor applies simultaneously to every finite p-norm rather than requiring separate arguments.
  • No subexponential algorithm can approximate SVP to the stated factor unless the assumption on NP fails.
  • Exact SVP inherits deterministic hardness in the Euclidean norm as a special case of the approximation result.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If the hardness holds, lattice-based cryptographic primitives would retain security even when instantiated with non-Euclidean norms.
  • The deterministic technique might extend to other lattice problems such as the closest vector problem under similar assumptions.
  • A concrete next step would be to check whether the reduction can be made to work for p equal to infinity or for other geometric problems on lattices.

Load-bearing premise

NP does not admit algorithms that run in time exponential in any positive power of n less than 1.

What would settle it

Either a deterministic polynomial-time algorithm that approximates shortest vectors to within 2^{(log n)^{1-o(1)}} for some finite p, or a subexponential-time algorithm for an NP-complete problem.

Figures

Figures reproduced from arXiv: 2604.01451 by Amit Sahai, Isaac M Hair.

Figure 1
Figure 1. Figure 1: (Left) An example 0/1 matrix P with N = 3 columns and M = 3 rows. (Right) The 2-fold VF tensor product of P, denoted as T = [PITH_FULL_IMAGE:figures/full_fig_p009_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: An example sequence of matrices P, Q, and R. Each (empty) white square is a zero entry, and each red bar is a row taken from a reduced Vandermonde matrix. The last few steps are as follows: First, we append a width-h q/(log M) 100 reduced Vandermonde matrix W to A∥R [PITH_FULL_IMAGE:figures/full_fig_p011_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: An example matrix C. As in [PITH_FULL_IMAGE:figures/full_fig_p011_3.png] view at source ↗
read the original abstract

We show that, assuming NP $\not\subseteq$ $\cap_{\delta > 0}$DTIME$\left(\exp{n^\delta}\right)$, the shortest vector problem for lattices of rank $n$ in any finite $\ell_p$ norm is hard to approximate within a factor of $2^{(\log n)^{1 - o(1)}}$, via a deterministic reduction. Previously, for the Euclidean case $p=2$, even hardness of the exact shortest vector problem was not known under a deterministic reduction.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. The paper claims that, assuming NP ⊈ ∩_{δ>0} DTIME(exp n^δ), the shortest vector problem for lattices of rank n in any finite ℓ_p norm is hard to approximate within a factor of 2^{(log n)^{1-o(1)}}, via a deterministic Karp reduction. This strengthens prior work by derandomizing randomized techniques through explicit constructions that preserve lattice rank and the target factor uniformly across all finite p, including the Euclidean case p=2 where even exact SVP hardness was previously unknown under deterministic reductions.

Significance. If the result holds, it is a significant contribution to the deterministic complexity of lattice problems. The deterministic reduction from a standard subexponential hardness assumption to GapSVP in every finite ℓ_p norm, achieved via explicit constructions without increasing rank or weakening the 2^{(log n)^{1-o(1)}} factor, provides a uniform treatment across norms and removes reliance on randomness. This is a clear technical strength that could support further derandomization results in the area.

minor comments (2)
  1. [Abstract] The abstract states the main claim clearly but could briefly note the explicit construction technique used for derandomization to give readers an immediate sense of the proof strategy.
  2. [Section 4] In the time-complexity accounting for the reduction, the precise dependence on the lattice rank n should be stated explicitly when bounding the overall running time under the subexponential assumption.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive assessment of our work and the recommendation to accept. We are pleased that the uniform deterministic hardness result for GapSVP across all finite ℓ_p norms, including the Euclidean case, is viewed as a significant contribution.

Circularity Check

0 steps flagged

No significant circularity identified

full rationale

The paper establishes hardness of approximating the shortest vector problem (SVP) in any finite ℓ_p norm via a deterministic Karp reduction from a standard complexity assumption (NP ⊈ ∩_δ DTIME(exp n^δ)). The derivation chain consists of explicit derandomization constructions that preserve lattice rank n and the target approximation factor 2^(log n)^{1-o(1)} uniformly across p. No step reduces by construction to a fitted parameter, self-definition, or unverified self-citation chain; the source problem's hardness is external to the target SVP instance. The result is therefore self-contained against the stated assumption with no load-bearing circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on one standard complexity assumption with no free parameters or invented entities.

axioms (1)
  • domain assumption NP is not contained in ∩_{δ>0} DTIME(exp n^δ)
    This is the explicit hypothesis stated in the abstract from which the hardness follows via deterministic reduction.

pith-pipeline@v0.9.0 · 5375 in / 1240 out tokens · 31457 ms · 2026-05-13T21:11:40.433406+00:00 · methodology

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Reference graph

Works this paper leans on

46 extracted references · 46 canonical work pages

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    In particular, case (1) enforces that the lattice vector is not only of small norm but also in{−1,0,1} N

    For all nonzero vectorsx∈Z M, we have∥xB∥ 0 ≥2h. In particular, case (1) enforces that the lattice vector is not only of small norm but also in{−1,0,1} N. Theorem 3.2 implies Theorem 3.1 via direct tensoring. Proof of Theorem 3.1 using Theorem 3.2.Fix any constantp≥1, and use the reduction from Theorem 3.2 to get an integer matrixB∈Z M×N , where1≤M≤exp ¶ ...

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    The first case also maintains thatx ′B′ ∈ {−1,0,1} N ′

    For all nonzero vectorsx ′ ∈Z M ′ , we have∥x ′B′∥0 ≥2 n1/log logn hn1/log logn . The first case also maintains thatx ′B′ ∈ {−1,0,1} N ′ . For all finitep≥1, theℓ p norm of an integer vectorw ′ havingxnonzero entries is at leastx 1/p, and this is realized with equality when the entries ofw ′ are in{−1,0,1}. So cases (1) and (2) from above have the followi...

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    inner verifier

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    DenoteH’s indicator matrix asP∈ {0,1} M×N , and letT= A∥Q be the(t, q)-VF tensor product ofP

    (Expansion) Every vertex subsetV ′ ⊆Vfully contains at most(|V ′|/N)dM+βMhyperedges. DenoteH’s indicator matrix asP∈ {0,1} M×N , and letT= A∥Q be the(t, q)-VF tensor product ofP. The following holds for all vectorsx∈Z M q such thatxA=0, and all parametersδ∈[0,1]. LetE ′ be the subset of[M] q containing all indices for the nonzero entries ofx. If|E ′|> M q...

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    DenoteH’s indicator matrix asP∈ {0,1} M×N

    (Expansion) Every vertex subsetV ′ ⊆Vfully contains at most(|V ′|/N)dM+βMhyperedges. DenoteH’s indicator matrix asP∈ {0,1} M×N . For all positive integersq, for all(t, q)-legal subsetsE ′ ⊆[M] q, and for all parametersδ∈[0,1], the following holds. If|E ′|> M qδd (1−βt)q , then|N (q) P (E′)|> N qδ. Proof.We give a proof by induction on the tensoring expone...

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    For reference, we also re-state the QRDH problem

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    As shorthand, we refer to the problem as(N, M, d, r, α, β)-QRDH

    Every vertex subsetV ′ ⊆Vfully contains at most(|V ′|/N)dM+βMhyperedges. As shorthand, we refer to the problem as(N, M, d, r, α, β)-QRDH. We refer torandαas thecompleteness parameters, andβas thesoundness parameter. We show in Section 6 that a modification of Khot’s quasi-random PCP [Kho06], combined with tools from a paper by Khot and Saket [KS16], gives...

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    Notice thatAis an integer matrix withM q rows andqM q/tcolumns, andQis an integer matrix withM q rows andN q columns

    LetT= A∥Q be the(t, q)-VF tensor product ofP. Notice thatAis an integer matrix withM q rows andqM q/tcolumns, andQis an integer matrix withM q rows andN q columns. All entries of Aare nonnegative and less than3M q, andQis a 0/1 matrix

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    LetV∈Z M q×w be an(a, w)reduced Vandermonde matrix, whereais a prime satisfyingM q < a < 3M q. Index the firstM q rows ofVusing distinct elements of[M] q. For eachv∈[N] q, we construct a matrixR (v) ∈Z M q×w usingQas follows: • For eache∈[M] q, do: –IfQ e,v = 0, then setR (v) e =0 w. –Otherwise, setR (v) e =V e. Now letRbe the horizontal concatenation of ...

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    LetW∈Z M q×h/n be an(a, h/n)reduced Vandermonde matrix, whereais a prime satisfying M q < a <3M q

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    Suppose the starting SAT instance was satisfiable. Then there exists a subsetΠ ′ ⊆Πof at most half the locations in the proof such that Pr Q [Q⊆Π ′]≥(1−O(1/d))·(1/2) d−1

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    Then for all subsetsΠ ′ ⊆Πof at most half the locations in the proof, Pr Q [Q⊆Π ′]≤(1/2) d + 1/220d

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    Then for allζ∈[0,1]and for all subsetsΠ ′ containing aζfraction of the locations in the proof, we have Pr Q [Q⊆Π ′]≤ζ d + 1/220d

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