Magnetar --- SLH-DSA (FIPS 205) for Lux

Magnetar is the hash-based PQ leg. SLH-DSA has no aggregatable structure, so the SOUND production primitive is per-validator standalone (N independent signatures); the threshold variants either relocate trust into attested hardware (TEE pool) or are research-grade (permissionless THBS-SE, which reconstructs the master at the public combiner).

Regime	Construction	Posture	Where
Public-BFT consensus (DEFAULT, production)	Per-validator standalone --- each validator holds its own FIPS 205 keypair, signs independently, consensus collects N signatures into a ValidatorAggregateCert	SOUND. No DKG, no dealer, no reconstruction.	standalone.go
Trusted-hardware / custody (opt-in, production)	TEE-attested combiner pool	SOUND under an honest trust model: the seed is reconstructed inside a measured enclave on t hosts that must agree --- trust-relocation (adds a host to the TCB), NOT MPC.	luxfi/threshold/protocols/slhdsa-tee
Permissionless t-of-n threshold	THBS-SE --- t-of-n committee, slot-bound commit-and-reveal, anyone-can-combine public combiner	RESEARCH-ONLY. The public combiner RECONSTRUCTS the full FIPS 205 master every signature (ASSEMBLE-INVARIANT.md). NOT no-leak.	thbsse.go, thbsse_field.go, thbsse_assemble.go, slhdsa_internal.go

All three produce FIPS 205 wire bytes that an unmodified verifier accepts. That is a correctness/interop property; it says nothing about confidentiality. See BLOCKERS.md for the sound/open/falsely-closed breakdown.

Per-validator standalone (public-BFT primary)

sk, pk, _ := magnetar.PerValidatorKeypair(params, rng)
sig, _    := magnetar.ValidatorSign(sk, rng, message)
// ... collected at the consensus layer ...
cert, _   := magnetar.BuildAggregateCert(params, signers, pubkeys, sigs)
valid, _  := magnetar.VerifyAggregateCert(cert, message, knownValidators)

No DKG, no shared seed, no aggregator-in-TCB. Wire size grows linearly with the quorum (N x |sigma|). The Z-Chain Groth16 rollup compresses the cert to ~192 bytes for long-term storage; the rollup is a separate primitive (lux-zchain spec).

THBS-SE (permissionless threshold)

key, _   := magnetar.NewThbsSeKey(params, t, committee, setupRng)
// Per-party Round-1 / Round-2 over the slot binding ...
r1i, r2i, _ := magnetar.ThbsSeRound1(params, key.Shares[i], binding, msg, guard, rng)
// ... any peer (the "public combiner") collects t valid r1/r2 pairs ...
sig, ev, _  := magnetar.Combine(magnetar.ThbsSeCombineInput{
    Key: key, Binding: binding, Message: msg, Round1: r1s, Round2: r2s,
})
// sig.Bytes is canonical FIPS 205; verifies under unmodified circl.slhdsa.Verify.

Setup --- two equivalent paths

Dealer setup (KAT-reproducible). NewThbsSeKey samples a master, byte-shares it via Shamir over GF(257), and zeroizes the master before return. The dealer machine is in the TCB FOR SETUP ONLY; once the function returns, no party (including the dealer) holds the master. Recommended for foundation-HSM single-host bootstrap and KAT replay.

Dealerless PVSS-DKG setup (RunDKG). Each committee party runs NewPVSSPartyState independently, publishes a PublicContribution (per-coefficient hash commitments only), and distributes private share rows over authenticated channels. The PRODUCTION path (RunDKG) publishes NO constant-term reveals, so the master is not reconstructible from the transcript. Any third party collates the public payloads into a PVSSTranscript and invokes NewThbsSeKeyFromDealerlessDKG to assemble the canonical ThbsSeKey. (A separate RunDKGSimulationOpenRevealTestOnly, gated behind an explicit hazard ack, runs the leaking open-reveal mode for KAT replay only.):

// Each party i runs in its own process.
state_i, _ := magnetar.NewPVSSPartyState(params, t, committee, uint32(i+1), rng)
contrib_i  := state_i.PublicContribution()  // broadcast publicly
share_to_j, _ := state_i.ShareTo(uint32(j+1))  // send privately to j
reveal_i := state_i.RevealMsg()              // broadcast publicly at Round 2

// Any auditor (or any party) collates the public-form transcript
// and assembles the canonical ThbsSeKey.
transcript := &magnetar.PVSSTranscript{
    Params: params, Committee: committee, Threshold: t,
    Contributions: contribs, Reveals: reveals,
    ReceivedShares: receivedShares, SetupTr: setupTr,
}
key, _ := magnetar.NewThbsSeKeyFromDealerlessDKG(transcript)
// key is byte-shape identical to the dealer-path output for the
// implicit master M = sum_{i in Q} m_i mod 257 byte-wise.

What the production dealerless path guarantees (and what it does not). The RunDKG transcript carries no constant-term reveals, so the master is not reconstructible from the transcript by observers. It does NOT make "no party ever holds the master" true: deriving the group public key needs pk = SLH-DSA.PK(M) (a hash tree over M), so deriveDKGPublicKey reconstructs M transiently at whoever derives pk and zeroizes it. That reconstruction is inherent (TEE/MPC only avoid it). Naming the buffer lagrangeScratch is not a security property. See BLOCKERS.md (P2) and RunDKG's HONEST LIMITATIONS in pvss_dkg.go. The production path also does NOT robustly exclude malicious dealers at DKG time (hash commitments aren't openable without revealing m_i); malformed shares are caught at sign time.

RunDKGSimulationOpenRevealTestOnly runs the full n-party protocol in one process in open-reveal mode for KAT replay only; it requires an explicit hazard ack and its transcript REVEALS the master.

THBS-SE reveal discipline. A revealed value is the per-round mask r_i, the masked share s'_i = share_i XOR r_i, the public commit hash, and the final signature. The share envelope is per-slot and the slot guard refuses same-slot re-emission.

The public combiner reconstructs the master. Any peer can run Combine (it is a pure function of public inputs), but it RECONSTRUCTS the full FIPS 205 master into derivedMaterial to produce the signature (ASSEMBLE-INVARIANT.md). So there IS effectively a host in the TCB at sign time: whoever runs Combine sees the seed. This is why the permissionless THBS-SE path is research-grade. The earlier claim that the "strict-atom Combine closed the transient-seed gap" was proof by rename (it avoids the variable name seed, not the reconstruction); see BLOCKERS.md::MAGNETAR-STRICT-ATOM (OPEN).

Slot binding: every signature is bound to (chain_id, epoch, slot, height, committee_id, message_domain). The binding flows into the cSHAKE256 commit transcript AND into the FIPS 205 ctx string at sign time, so a verifier holding the slot tuple derives ctx independently and routes through unmodified slhdsa.Verify.

Slashing evidence: a party that signs two distinct messages at the same slot emits a ThbsSeEquivocationError carrying a wire- shaped ThbsSeEvidence blob that any third party can verify via VerifyThbsSeEvidence --- pure function, no committee state required. Malformed shares produce typed ThbsSeShareEvidence blobs verified via VerifyThbsSeShareEvidence.

Over-selected committee: with (n, t) and n > t, up to n - t silent withholders are tolerated. Any t valid Round-2 reveals produce byte-equal final signatures.

Why per-validator standalone is the public-BFT default

SLH-DSA is hash-based; it has no algebraic structure that admits FROST-style linear share-aggregation. The literature confirms:

• Cozzo and Smart, EUROCRYPT 2019 Sharing the LUOV: every internal SHAKE/SHA-2 evaluation in an HBS scheme is a non-linear function of the secret seed.
• Bonte, Smart and Tan 2023 Threshold SPHINCS+: exhaustive infeasibility analysis. There is no efficient t-of-n SLH-DSA scheme producing a single FIPS 205-shaped signature without either (a) reconstructing the seed in some combiner process or (b) running full MPC over the SHA-256/SHAKE hash tree (multi-second per signature, multi-megabyte of comms).

THBS-SE chooses (a) with a PUBLIC COMBINER. "Anyone can combine", but whoever does RECONSTRUCTS the seed --- so the combiner IS effectively a host in the TCB at sign time, which is why THBS-SE is research-grade, not production. The TEE pool chooses (a) inside attested hardware (trust-relocated, not removed). The per-validator standalone path sidesteps (a) and (b) entirely by emitting N independent signatures and is the production default.

Status

Field	Value
Standard	FIPS 205 SLH-DSA
Production primitive	Per-validator standalone (standalone.go) --- SOUND
Opt-in production	TEE-attested combiner pool (luxfi/threshold/protocols/slhdsa-tee) --- sound under attested-hardware trust
Research-only	THBS-SE permissionless threshold --- reconstructs the master at the public combiner
Reference implementation	ref/go/pkg/magnetar/ --- pure Go, depends on cloudflare/circl/sign/slhdsa v1.6.3
KAT vectors	vectors/{keygen,sign,verify,thbsse-sign}.json (deterministic regeneration)
Wire identity	All paths emit byte-identical FIPS 205 signatures; any unmodified slhdsa verifier accepts. Interop only --- not a confidentiality claim.
Cert-profile role	Polaris profile in luxfi/quasar (hash-based leg of the cross-family PQ profile)
Sibling primitives	Pulsar (FIPS 204 M-LWE), Corona (R-LWE) --- algorithmically distinct families

Headline tests

cd ref/go && GOWORK=off go test -count=1 -short -timeout 600s ./pkg/magnetar/...

• TestMagnetar_Wire_FIPS205Verifiable (wire_test.go) --- pins byte-identity between ValidatorSign output and unmodified cloudflare/circl/sign/slhdsa.Verify across all 3 SHAKE modes.
• TestThbsSE_Wire_FIPS205Verifiable (thbsse_test.go) --- pins the same identity for the THBS-SE public combiner output.
• TestThbsSE_RejectSeedReveal, TestThbsSE_RejectOversizedShareWireSize, TestThbsSE_RejectTamperedShareCommitMismatch, TestThbsSE_SlotReuseRejected, TestThbsSE_OverselectedCommittee, TestThbsSE_SlotBindingDomainSeparation --- the THBS-SE commit-binding / slot-binding gates. (The last two reject-tests were formerly mis-named ...UnselectedFORS / ...WOTS; THBS-SE shares the whole seed, so they test commit binding, not atom selection.)
• TestPVSS_DKG_ProductionTranscriptHidesMaster --- the production RunDKG transcript hides the master (P2 leak-fix regression gate); the open-reveal path reveals it (contrast).
• TestPVSS_DKG_ByteCompatWithDealerPath, TestPVSS_DKG_AdversarialReveals, TestPVSS_DKG_RobustnessAgainstMaliciousCommitments, TestPVSS_DKG_EndToEnd_SignAndVerify --- further DKG gates (the end-to-end test drives the production RunDKG path).
• BenchmarkThbsSE_Sign_5of7/Magnetar-SHAKE-192f --- end-to-end per-signature wall-clock at < 100 ms/op on Apple M1.
• TestKAT_ThbsSe --- deterministic vector replay at (n=7, t=4) x 3 modes x 3 messages.

Operator-controlled MPC custody

For deployments where an HSM-attested host is in the TCB by deployment policy (e.g. M-Chain bridge custody, A-Chain confidential compute), TEE-attestation-gated variants ship under luxfi/threshold/protocols/{slhdsa,mldsa,rlwe}-tee via the lux/mpc sibling tree --- NOT in this package. Magnetar's role is the public-BFT and permissionless-threshold surface; the operator- controlled variants are decomplected into their own primitive slot.

Where this is used

The hash-based leg of the Polaris cert profile in luxfi/quasar --- the maximum-assurance cross-family profile pairing lattice PQ (Pulsar M-LWE + Corona R-LWE) with hash-based PQ (Magnetar SLH-DSA).

Documents

• SPEC.md --- normative construction specification.
• THBS-SPEC.md --- THBS-SE normative spec (slot binding, commit-reveal, public-combiner, evidence).
• CHANGELOG.md --- release-by-release framing.
• DEPLOYMENT-RUNBOOK.md --- public-BFT default + the v1.0 honest open item (transient seed reconstruction at the public combiner).
• BLOCKERS.md --- sound / open / falsely-closed enumeration (THBS-SE reconstructs the master; PVSS-DKG leak fix; TEE trust model).
• CRYPTOGRAPHER-SIGN-OFF.md --- internal review (standalone only).
• TRUSTED-COMPUTING-BASE.md --- TCB enumeration.
• PROOF-CLAIMS.md --- per-property proven/asserted/open (no mechanized threshold proof exists).
• AXIOM-INVENTORY.md --- assumed-axiom enumeration.
• FIPS-TRACEABILITY.md --- line-by-line FIPS 205 conformance trace.
• PATENTS.md --- patent-status notes.
• LICENSING.md --- license terms.
• SUBMISSION.md / NIST-SUBMISSION.md / SUBMISSION-STATUS.md --- NIST MPTC submission framework.
• AUDIT-2026-06.md --- 2026-06 production-readiness audit (public-permissionless-chain safety, TEE integration story, GPU acceleration story, canonical-name positioning).
• TEE-INTEGRATION.md --- TEE-attested production surface spec (SEV-SNP today, TDX + NRAS post-#222, operator-side wiring).
• GPU-PORT-PLAN.md --- v1.3 GPU acceleration port plan (four batched FIPS 205 hash-tree kernels at lux-private/gpu-kernels/ops/crypto/slhdsa/).
• SECURITY.md --- threat model + strict-PQ profile.
• ASSEMBLE-INVARIANT.md --- what the THBS-SE Combine path actually does (it reconstructs the master; "strict-atom" was proof-by-rename).

Build

cd ref/go && GOWORK=off go build ./...
cd ref/go && GOWORK=off go test -count=1 -short -timeout 600s ./pkg/magnetar/...
cd ref/go && GOWORK=off go test -count=1 -race -short -timeout 600s ./pkg/magnetar/...

Citations

• NIST FIPS 205 (2024). Stateless Hash-Based Digital Signature Standard.
• Cozzo, D. and Smart, N. P. (2019). Sharing the LUOV. EUROCRYPT.
• Bonte, C., Smart, N. P. and Tan, T. (2023). Threshold SPHINCS+: Practical Threshold Signatures from a Stateless Hash-Based Signature.
• McGrew, D., Wallace, C. and Whyte, W. (2019). Threshold Hash-Based Signatures. IACR ePrint 2019/793.
• Schoenmakers, B. (1999). A simple publicly verifiable secret sharing scheme and its application to electronic voting. CRYPTO.
• Shamir, A. (1979). How to share a secret. Communications of the ACM.