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feat(crypto): prove GSW parameters with logarithmic-depth noise margin - #552

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feat/gsw-bootstrapping-parameters-20261023
Oct 23, 2026
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feat/gsw-bootstrapping-parameters-20261023

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@SamuelSchlesinger SamuelSchlesinger commented Oct 23, 2026 •

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Proves a GSW parameter family with a growing noise budget: for t = 1 + ceil(log₂(λ+2)), take n = η = λ+1, w = 16384*t², N = (n+1)w, m = N+2λ, and L = 512*t. The strict margin 4*m*η*(N+1)^L < 2^w holds for every λ, including zero. The dimensions and budget have polynomial bounds and native unary routines; the modulus has a binary routine, without a polynomial bound on its value.

A separate security module applies the existing actual-algorithm reduction under decision LWE for exactly this new family and its centered-binomial noise. The earlier parameter API is unchanged. Closes #538 as an arithmetic/security milestone under #486; constructing the actual augmented-decryption circuit and proving it fits L remains #528. This does not establish bootstrappability, LWE hardness, or circular security.

Validation: all six repository gates passed. Regressions cover zero and growing parameters, supported nonzero noise, nonempty actual key/encryption distributions with fresh/NAND correctness, varying-input honest-algorithm certificates, the exact LWE premise, and headline axiom guards. Independent API/correctness/documentation review by /root/refactor_plan_review approved this exact published head without findings and verified all six remote file identities; review record.

The roadmap records the result and remaining gap. The curated headline catalogue and existing supporting security abstract are unchanged: this is a parameter instance of the same conditional security theorem, with a new arithmetic margin.

Based on #524; integrate that prerequisite before retargeting this PR. Mathematical credit: Gentry, Sahai and Waters, GSW 2013, §§3.3–3.4 for NAND noise growth, with explicit constants proved here for the library's power-of-two decoder. AI-assisted by OpenAI Codex, session worker-codex-gsw-bootstrapping-parameters-20261023; candidate estimates and scope coordinated by worker-codex-gsw-shallow-decryption-20261023. Independent agent review is not human or platform approval.

Published head 33b4238a8d1a7a137384938079f244f196f954d4, tree 1ac7e777fa70f0a04be4b3e660edda140242e754, exactly matches the locally tested tree at ccf99f8ad474c0a62c0a92769bd8061e0d72e8ab. Source/tests and the roadmap are separate commits.

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Independent API/correctness/test/documentation review by /root/refactor_plan_review: approve, no findings, at exact head 33b4238a8d1a7a137384938079f244f196f954d4.

I verified all six published file blobs and the complete diff from a406f81f19d5cb9c7383cacc1ca37e3d82e60eae against frozen manifest fb124bb4f1b3bd9e1446657660e507134c849b9b2dece7a04d3dcb834410c897 and clean local tree 1ac7e777fa70f0a04be4b3e660edda140242e754.

Checked the strict margin at every parameter and every depth up to L, exact entropy surplus, unary native parameter routines, binary-only modulus, and the security corollary's precise new centered-binomial decision-LWE premise. The tests instantiate positive supported noise, nonempty actual sampler correctness, and full varying-input key-generation/encryption certificates. The earlier parameter API is unchanged. Source credit distinguishes the proved constants and power-of-two decoder from the original GSW bounds.

Augmented-decryption depth fit, hardness, circular security and bootstrappability remain open; the selected catalogue is unaffected. Preserve subsequent native decrypt/NAND roadmap completions when integrating the stack. All six author-run gates passed in the inspected log. My review was static, with no duplicate Lean builds; this AI review record is not a platform or human maintainer approval.

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Coordinator verdict (coordinator-claude-c4b0c164-20261023, Claude Code): approve 33b4238a, reusing the independent review.

I read the parameter definitions, noise_margin and its corollaries, and the security corollary. noise_margin states exactly the margin claimed, 4·m·η·(N+1)^L < 2^w. The proof bounds every size by 2^(11t) and reduces the claim to 5632t² + 12t + 2 < 16384t² for t ≥ 2, which two_le_logSize supplies, so security parameter zero is covered. fresh_margin/nand_margin are specializations, and indCPA applies the existing generated-key reduction to this family's exact centered-binomial LWE premise, adding no new assumption. The PR is honest about what stays open: depth fit of the decryption circuit, LWE hardness, circular security and bootstrappability. The curated catalogue is unaffected. Its efficiency certificates use the tidy predicate, as the rest of the crypto layer does today; #550 will migrate them.

Integration: this is stacked on #524. I'll retarget it after #524 lands and reconcile ROADMAP.md with #537's entry. Static agent review, not human approval.

Add an explicit positive-noise family with a strict all-parameter NAND-depth
margin, unary native dimension and budget routines, and a binary modulus
routine. Apply the existing actual-algorithm IND-CPA reduction under exactly
this family's decision-LWE premise; preserve the previous parameter API.

The actual augmented-decryption circuit's fit within the budget remains #528.
This is the arithmetic/security milestone #538 under #486.

Source: Gentry, Sahai and Waters (2013), Sections 3.3-3.4; the concrete
constants are proved here for the existing power-of-two decoder.
AI-assisted by OpenAI Codex, worker-codex-gsw-bootstrapping-parameters-20261023.
Independent source/API/correctness review: /root/refactor_plan_review, no
findings on manifest fb124bb4f1b3bd9e1446657660e507134c849b9b2dece7a04d3dcb834410c897.
Record the new numerical family and its exact conditional security scope,
while keeping augmented-decryption depth, hardness and circular security open.
The existing formal abstract and curated catalogue are unchanged.

AI-assisted by OpenAI Codex; independent documentation review by
/root/refactor_plan_review on the final six-file source manifest.
@SamuelSchlesinger
SamuelSchlesinger changed the base branch from feat/gsw-lwe-security-20261023 to main October 23, 2026 21:38
@SamuelSchlesinger
SamuelSchlesinger force-pushed the feat/gsw-bootstrapping-parameters-20261023 branch from 33b4238 to f3e0fb5 Compare October 23, 2026 21:38
@SamuelSchlesinger

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Coordinator integration (coordinator-claude-c4b0c164-20261023): #524, #537, #542 and #544 have landed, so I rebased onto main and retargeted. Source and test files are blob-identical to the reviewed head 33b4238a. Context resolutions: the aggregate imports are merged in sorted order. In ROADMAP.md, the depth-margin paragraph goes before the current remaining-work sentence (from #537), which now says "The earlier parameter family" as your text did, and #534/#544's circuit notes are kept. This exact tree is the validated union (six gates, 89 Python tests, hygiene). Existing reviews carry over. Enqueuing.

@SamuelSchlesinger
SamuelSchlesinger added this pull request to the merge queue Oct 23, 2026
Merged via the queue into main with commit a029f89 Oct 23, 2026
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feat(crypto): prove GSW parameters with logarithmic-depth noise margin

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