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Antje Worring df4c537c16 magnetar: remove proof-by-rename + circular proofs; honest threshold status

True no-reconstruction threshold SLH-DSA is impossible in the no-dealer /
no-preprocessing model a public, leaderless, permissionless chain needs
(Kondi-Kumar-Vanegas: extractable hash-based signatures cannot be thresholded
by black-box hash use). Stop pretending otherwise.

De-cheat:
  - DELETE the circular/vacuous proofs that manufactured false assurance:
    Magnetar_N1_Atom_Refinement.ec, Magnetar_N1_SHAKE_Expand.ec,
    Magnetar_N4_KeyDeriveStable.ec, lemmas/{Magnetar_CT,SLHDSA_Functional}.ec.
    The headline "strict-atom byte-equality" theorem was `apply <axiom that
    restates the theorem>`; the Lean side was `sorry`/`:= True`.
  - Re-open MAGNETAR-STRICT-ATOM (BLOCKERS): the public combiner DOES
    reconstruct the full FIPS 205 master every signature; the v1.1 "closure"
    only renamed identifiers. PROOF-CLAIMS / AXIOM-INVENTORY / TCB docs now say
    what the code does.
  - Re-label the name-grep "strict-atom" / "CT" checks as identifier-hygiene
    lint, NOT security or constant-time properties.
  - PVSS-DKG open-reveal (publishes the master to any observer) is gated as a
    TEST-ONLY path with HONEST LIMITATIONS; production does not rely on it.
  - Remove dead htRootCompute; staticcheck clean.

Honest three-leg posture (SPEC 1.0, BLOCKERS):
  - Permissionless production = INDEPENDENT FIPS 205 sigs + the weighted quorum
    certificate (luxfi/consensus), optionally STARK/FRI-compressed (luxfi/p3q).
    No key sharing, no reconstruction.
  - Trusted-hardware custody = TEE-attested combiner (trust-relocation, NOT MPC).
  - THBS-SE = RESEARCH-ONLY (transient seed reconstruction at the combiner);
    the T-SLH-DSA-MPC track (MPC over SHAKE) is the other research escape hatch.

Tests green (CGO=1, 71s). Net -923 lines.

2026-06-21 13:06:57 -07:00

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Magnetar --- design

Magnetar is the hash-based (FIPS 205 SLH-DSA) PQ leg of the Lux cross-family signature suite. This document states the architecture and why each path exists.

The fundamental constraint

SLH-DSA is a tree of hash computations: the secret is a SHAKE seed and signing traverses a hypertree of one-time / few-time signatures keyed by that seed. There is NO linear-aggregation identity (unlike FROST/Schnorr or the Raccoon-style ML-DSA threshold). The literature is explicit:

Cozzo & Smart, EUROCRYPT 2019, Sharing the LUOV: every internal SHAKE/SHA-2 evaluation is a non-linear function of the secret seed.
Bonte, Smart & Tan, 2023, Threshold SPHINCS+: there is no efficient t-of-n SLH-DSA scheme producing one FIPS 205-shaped signature without either (a) reconstructing the seed in some combiner process, or (b) full MPC over the SHAKE hash tree (multi-second, multi-megabyte per signature).
NIST IR 8214: SLH-DSA is the highest threshold-MPC cost among FIPS 20{3,4,5}.

True no-reconstruction threshold SLH-DSA is OPEN RESEARCH. Magnetar does not pretend otherwise. Instead it offers three paths chosen by deployment model.

The three paths

1. Per-validator standalone --- PRODUCTION DEFAULT (sound)

standalone.go. Each validator holds its own FIPS 205 keypair, signs the message independently, and the consensus layer collects N single-party signatures into a ValidatorAggregateCert. Verification counts valid signatures against the validator-set registry; the quorum decision lives at the consumer.

This is the sound primitive: there is no shared seed, no DKG, no dealer, and no reconstruction anywhere. It sidesteps both (a) and (b) by emitting N independent signatures. Wire size is N x |sigma| (a Z-Chain Groth16 rollup compresses it; separate primitive).

THIS IS THE DOCUMENTED PRODUCTION PRIMITIVE for public-BFT post-quantum consensus.

2. TEE-attested combiner pool --- OPT-IN PRODUCTION (sound under attested-hardware trust)

luxfi/threshold/protocols/slhdsa-tee. For deployments that genuinely need a SINGLE FIPS 205-shaped signature from a committee (custody, bridge signing), Magnetar routes Combine through a t-of-n attested-combiner pool, gated by the single profile function magnetarRefuseUnderStrictPQ.

Honest trust model: the seed is reconstructed in full, but INSIDE a measured enclave whose binary + firmware chain-validate to a vendor root (AMD KDS today; Intel TDX / NVIDIA NRAS are stubs). This is TRUST-RELOCATION --- it moves the reconstruction into attested hardware and ADDS that hardware (plus the attestation chain and the t hosts) to the TCB. It is NOT MPC and does NOT keep the seed secret from every party; the enclave sees it.

3. Permissionless THBS-SE --- RESEARCH-ONLY

thbsse.go + thbsse_field.go + thbsse_assemble.go + slhdsa_internal.go. A t-of-n committee, slot-bound commit-and-reveal, and an anyone-can-combine public combiner. The public combiner RECONSTRUCTS the full FIPS 205 master into one buffer every signature (ASSEMBLE-INVARIANT.md) and emits a byte-identical FIPS 205 signature.

Because whoever runs Combine sees the seed, there is effectively a host in the TCB at sign time. This path is RESEARCH-GRADE. It must not be presented as production or as "no host in the TCB". The earlier "strict -atom Combine closed the no-leak gap" claim was proof by rename (it avoids the variable name seed, not the reconstruction). See BLOCKERS.md::MAGNETAR-STRICT-ATOM (OPEN).

Setup: dealer, dealerless, or TEE

Dealer (NewThbsSeKey): one machine samples the master, byte-shares it over GF(257), and zeroizes it. The dealer is in the TCB for setup only. KAT-reproducible; recommended for foundation-HSM bootstrap.
Dealerless production (RunDKG): per-party PVSS with hash commitments; the transcript carries NO constant-term reveals, so the master is not reconstructible from the wire. BUT pk derivation reconstructs the master transiently (inherent: pk = SLH-DSA.PK(M) is a hash tree over M), and the path does NOT robustly exclude malicious dealers at DKG time (hash commitments aren't openable without revealing m_i). See RunDKG HONEST LIMITATIONS in pvss_dkg.go.
TEE: routes both pk derivation and Combine through attested hardware (trust-relocated).

A leaking open-reveal DKG (RunDKGSimulationOpenRevealTestOnly) exists for KAT replay only, behind an explicit hazard acknowledgement; its transcript reveals the master.

Parameter sets (FIPS 205 SHAKE)

Mode	NIST Category	sig bytes
SHAKE-192s	3	16224 (recommended)
SHAKE-192f	3 fast	larger sig, faster sign
SHAKE-256s	5	29792

SLH-DSA signatures are large (16-30 KB) vs ML-DSA (2-5 KB); the per-signature cost dominates economics, which is another reason the standalone path (no MPC ceremony) is the production default.

What is NOT claimed

No mechanized proof of any threshold property (the prior EC/Lean track was vacuous; see PROOF-CLAIMS.md).
No no-leak property for THBS-SE.
No robust-against-malicious-dealers property for the production DKG.
No external audit.

Use the per-validator standalone path for production public-BFT signing. Use the TEE pool when you are willing to trust attested hardware. Treat THBS-SE as research.

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