magnetar/TRUSTED-COMPUTING-BASE.md

TRUSTED-COMPUTING-BASE — Magnetar implementation TCB

What you must trust to rely on Magnetar's byte-equality correctness claim. Companion to PROOF-CLAIMS.md (proof scope) and DEPLOYMENT-RUNBOOK.md (operator-facing trust-model disclosure).

HONESTY NOTE: Magnetar's TCB is structurally simpler than Pulsar's because Magnetar ships NO mechanized refinement layer for the threshold overlay (no EasyCrypt theories specific to the overlay, no Lean ↔ EC bridges specific to the overlay, no Jasmin sources for the overlay). The FIPS 205 SLH-DSA single-party layer DOES have upstream formal artifacts available (libjade's SLH-DSA work) but Magnetar does not redistribute or re-verify them in this submission. That removes the overlay-specific proof-tool TCB but increases the trust placed in (i) the Go reference implementation review of the threshold overlay, (ii) KAT determinism, and (iii) the byte-equality test harness against the cloudflare/circl FIPS 205 verifier. See PROOF-CLAIMS.md for the honest framing.

§0 Layered trust bases

The Magnetar byte-equality claim rests on three layered trust bases:

1. The FIPS 205 SLH-DSA standard — NIST FIPS 205 (2024). The single-party signing primitive's security analysis is NIST's; the Magnetar submission inherits it.
2. The Go reference implementation — ref/go/pkg/magnetar/ (~2200 LOC) plus cloudflare/circl/sign/slhdsa (the FIPS 205 single-party reference). Reviewed by code inspection + KAT replay
   • the TestN1_ByteEquality_* empirical byte-equality harness.
3. The trusted-computing base (TCB) below the implementation — this document.

If any element of the TCB is unsound, the implementation's correctness is unsound regardless of how clean the code review was.

§1 Implementation TCBs

§1.1 Reference implementation (Go)

Component	Trust	Mitigations
Magnetar Go reference (this repository)	Go standard-library correctness, crypto/rand randomness quality, transcript-hash primitives in transcript.go (cSHAKE256 / KMAC256), Shamir / Lagrange in shamir.go, DKG protocol in dkg.go, threshold-sign protocol in threshold.go, Combine in combine.go	Reviewed by code inspection; KAT replay (vectors/*.json regenerated byte-stably); TestN1_ByteEquality_* empirical byte-equality vs single-party FIPS 205
github.com/cloudflare/circl/sign/slhdsa	Cloudflare's audited Go reference implementation of FIPS 205 SLH-DSA. Used for: scheme-seed derivation (Scheme.DeriveKey), SignDeterministic, Verify.	Version pinned in go.mod. circl is the canonical mainstream Go FIPS 205 implementation; community-audited at Cloudflare scale.
golang.org/x/crypto/sha3	cSHAKE256, KMAC256, TupleHash256 primitives (Go-stdlib-style).	Version pinned in go.mod.
crypto/subtle	Constant-time byte-blob compare. Standard library. (Note: Magnetar uses local ctEqualSlice / ctEqual32 constant-time helpers in transcript.go rather than crypto/subtle.ConstantTimeCompare for direct legibility; the algorithm is identical: scan every byte with `diff	= a[i] ^ b[i], return diff == 0`.)

§1.2 Production targets (out of scope for v0.3.0)

Target	Status
Optimized Rust crate	TODO — not in this submission
C library + FFI	TODO — not in this submission
WASM build	TODO
no_std embedded	TODO
C++ port	TODO — a future cross-runtime byte-equality harness (matching Pulsar's luxcpp/crypto/pulsar/ and Corona's luxcpp/crypto/corona/) is a possible Tier A → Tier A++ evidence enhancement

For each future target, an independent constant-time audit + KAT cross-validation + binding-level fuzzing is required before considering it "production." The byte-equality claim does NOT automatically transfer to these targets — each target's correctness must be re-verified.

§2 Build TCBs

Layer	What you trust	Reproducibility
Go toolchain	The Go compiler used to build the reference. The go.mod directive pins the language version.	Hard-pinned in go.mod; go.sum enforces module checksums.
scripts/cut-submission.sh	The cut orchestrator's correctness — that it produces deterministic outputs from a fresh checkout.	Mirrors Pulsar's pattern; runs build → tests → KAT-regen verification → tar.
scripts/check-high-assurance.sh	The high-assurance gate's correctness — go build + go vet + secret-log smoke scan. Skips proof-tool checks since Magnetar ships none for the overlay layer.	Honest about what's checked and what's not; documented in the script header.
ref/go/cmd/genkat	Deterministic regeneration of KAT vectors.	The genkat tool consumes fixed seeds and produces byte-stable JSON output; re-running on a clean checkout produces byte-identical files.

§3 What the TCB does NOT include

Magnetar's TCB is structurally simpler than Pulsar's because Magnetar ships no mechanized refinement layer for the threshold overlay. The following are NOT in the Magnetar TCB:

• EasyCrypt prover (Pulsar trusts it; Magnetar has no EC theories for the overlay layer)
• Lean 4 + Mathlib (Pulsar uses Lean-bridged algebraic axioms for Shamir / Lagrange identities; Magnetar has none of its own — closure plan is cross-citation to Pulsar's bridges, since the underlying GF(257) algebra is identical)
• Jasmin verified compiler (Pulsar's threshold layer is in Jasmin; Magnetar's is pure Go)
• OCaml runtime (EC is OCaml; Magnetar has no EC)
• jasmin-ct (Magnetar's CT evidence is local-helper ctEqualSlice / ctEqual32 review + the cloudflare/circl upstream constant-time claims for the FIPS 205 single-party layer; statistical CT measurement is roadmap)

What IS in the Magnetar TCB but NOT in Pulsar's:

• Greater dependence on the Go reference review of the threshold overlay. Pulsar can fall back to the EC refinement chain if a Go reviewer misses a bug in the threshold layer; Magnetar's only line of defense for the overlay is reviewer + KAT determinism + the TestN1_ByteEquality_* harness against single-party FIPS 205.
• Greater dependence on cloudflare/circl's FIPS 205 implementation. Pulsar's spec target (FIPS 204) is implemented both by cloudflare/circl AND independently by BoringSSL FIPS / AWS-LC / OpenSSL 3.0 (interop targets exist). Magnetar's spec target (FIPS 205) is at a less mature interop point — circl is the canonical Go implementation, but the mainstream third-party FIPS 205 implementations (BoringSSL, OpenSSL) are still landing at submission time.

§4 What the TCB does NOT cover

These are explicitly NOT part of the trust base for Magnetar's byte-equality correctness claim:

• Specific operating system (Linux, macOS, BSD, Windows) — the Go reference is OS-independent.
• Specific CPU architecture — Go compiles to amd64/arm64; both exercised in development.
• Network protocol stack — Magnetar's transport is out of scope.
• Storage layer — how KeyShare material is stored at rest is out of scope. Production deployments use HSM-backed share material or TEE-attested host configurations; see DEPLOYMENT-RUNBOOK.md.
• Key management policies — key lifecycle is application-level (governed by the consuming consensus layer, e.g. Quasar Polaris profile).
• Application code calling Magnetar — Magnetar's API contract is the trust boundary.

§5 TCB risks and mitigations

§5.1 Construction-soundness risk

Risk	Mitigation
FIPS 205 SLH-DSA has a latent cryptanalytic flaw	NIST FIPS 205 (2024) is the published standard with extensive cryptanalytic review. Lux tracks cryptanalysis literature; any flaw would prompt NIST guidance, which Magnetar would inherit. The fundamental hardness assumption (collision/preimage resistance of SHAKE) is conservative.
The Magnetar threshold lifecycle additions (byte-wise Shamir VSS, DKG, two-round commit-bind sign) have a latent bug	Per-protocol tests in ref/go/pkg/magnetar/dkg_test.go, threshold_test.go, kat_test.go, n1_byte_equality_test.go. Independent third-party audit is roadmap item, see BLOCKERS.md BLK-9. The byte-equality property to single-party FIPS 205 is the load-bearing N1 invariant; any threshold-layer bug that broke it would manifest in TestN1_ByteEquality_* failure.

§5.2 Implementation-correctness risk

Risk	Mitigation
Go reference implementation diverges from the construction	TestN1_ByteEquality_* runs end-to-end DKG → threshold-sign → Combine and asserts byte-equality with slhdsa.SignDeterministic(KeyFromSeed(reconstructed_seed), msg, ctx). Divergence = test failure.
KAT vectors are subtly wrong	Deterministic generation from fixed seeds via ref/go/cmd/genkat. The KAT replay test (kat_test.go) validates that the package implementation reproduces every KAT entry verbatim.
cloudflare/circl/sign/slhdsa has a bug in FIPS 205 implementation	circl is the canonical mainstream Go FIPS 205 implementation; community-audited at Cloudflare scale. A circl bug would also affect any other Go consumer of FIPS 205. Closure: cross-implementation verifier harness against a non-Go FIPS 205 implementation (e.g., pq-crystals reference C, BoringSSL when SLH-DSA lands) is roadmap, see BLOCKERS.md BLK-6.
Hash-suite implementation bug (cSHAKE256 / KMAC256)	golang.org/x/crypto/sha3 is a widely-used standard library implementation; bugs are rare and quickly patched. The Magnetar Shamir / Lagrange / mix operations route every call through transcript.go so any drift is a single-file change.

§5.3 Build / reproducibility risk

Risk	Mitigation
scripts/cut-submission.sh produces non-deterministic output	The build is deterministic from fixed seeds; reproducible-build property is checked at every cut. The KAT regen step explicitly compares regenerated vectors against committed copies.
Toolchain version drift between commits	go.mod pin + go.sum enforcement.
KAT drift across runs	ref/go/cmd/genkat consumes only fixed seeds and committed config; output is byte-stable. The cut script diffs regenerated KATs against committed copies and fails on any divergence.

§5.4 Side-channel risk

Risk	Mitigation
Timing leakage on secret-dependent paths in the threshold overlay	Constant-time helpers (ctEqualSlice, ctEqual32) are used for every commit verification and public-key equality check. Secret-dependent branches absent from verify.go, sign.go, and the Combine commit-verify gate. Statistical validation via dudect is NOT yet in place — roadmap item, see PROOF-CLAIMS.md §3.4.
Timing leakage in the single-party FIPS 205 layer	cloudflare/circl/sign/slhdsa documents constant-time properties per FIPS 205 §6.3 guidance; libjade has SLH-DSA formal CT artifacts for the broader ecosystem. Magnetar does not redistribute these but inherits the upstream guarantees.
Memory-access / cache-timing leakage	Not addressed at the software level. Production deployments should use TEE attestation (SGX, SEV-SNP, TDX) per DEPLOYMENT-RUNBOOK.md §1 ("v0.1 reveal-and-aggregate trust caveat").
Secret-buffer lifetime / coredump risk	The Combine path explicitly zeroizes every secret-bearing buffer (masterSeed, sk_rec, byteSumBytes, mixInput) at every error and success exit (combine.go). No defer-based zeroization; explicit at the return site for locally-legible secret lifetime.

§6 Independent verification protocol

To independently verify Magnetar's claims, a reviewer should:

1. Clone the repo at the submission tag.
2. GOWORK=off go build ./... — expect clean build.
3. GOWORK=off go test -count=1 -short -timeout 240s ./ref/go/pkg/magnetar/ — expect all tests passing, including TestN1_ByteEquality_* across (3,2), (5,3), (7,4).
4. Backup vectors/, run GOWORK=off go run ./ref/go/cmd/genkat -out=vectors/, then diff -qr vectors_backup/ vectors/ — expect zero differences (KAT determinism).
5. Read the Go reference implementation:
   • params.go, types.go — public types + FIPS 205 parameter sets
   • keygen.go, sign.go, verify.go — single-party FIPS 205 dispatch
   • shamir.go — byte-wise Shamir VSS over GF(257)
   • transcript.go — cSHAKE256 / KMAC256 / SP 800-185 helpers
   • dkg.go — three-round DKG
   • threshold.go, combine.go — two-round threshold sign + aggregator
   • zeroize.go — secret-buffer wipes
6. Cross-reference with FIPS 205 (NIST 2024) §10.1 (parameter sets), §10.2 (Sign), §10.3 (Verify).
7. Cross-reference with SPEC.md §3 (DKG), §4 (threshold sign), §6 (byte-equality claim), §7 (trust model).

If all 7 steps pass, the trust base reduces to the TCB enumerated in this document.

§7 What this means for downstream consumers

For a downstream consumer (e.g., a Quasar consensus chain incorporating Magnetar as the hash-based PQ leg of the Polaris profile):

• The byte-equality claim is conditional on the TCB. If you change the Go toolchain, port to a different runtime, or modify the hash suite, the claim's transferable guarantees attenuate.
• For FIPS 140-3 module validation, Magnetar's path is via the FIPS 205 SLH-DSA standard (NIST). The single-party FIPS 205 layer in cloudflare/circl is independently validatable when FIPS 205 modules ship; the threshold overlay is not subject to FIPS 140-3 directly (there is no NIST standard for threshold SLH-DSA).
• For NIST MPTC review, Magnetar's role is the algorithm-level reference + production lifecycle artifacts; module packaging + external audit are downstream.
• For threshold signing in a Quasar Polaris deployment, Magnetar is the hash-based PQ kernel; the consuming consensus layer is responsible for the chain-of-custody and validator-rotation orchestration. The Magnetar reshare protocol (v0.4 roadmap) will provide the Class N4-analog primitive when it lands.

§8 Honest comparison to Pulsar's and Corona's TCBs

TCB element	Pulsar	Magnetar	Corona
EasyCrypt prover	YES (foundation of refinement proof, 13 files, 0/0 admits)	NO (no EC theories for the overlay layer)	NO
Lean 4 + Mathlib	YES (5 Lean-bridged axioms)	NO (cross-citation closure on roadmap; Shamir/Lagrange algebraically identical to Pulsar's GF(257))	NO
Jasmin verified compiler	YES (threshold layer in Jasmin)	NO (pure Go; libjade covers SLH-DSA single-party but is not redistributed here)	NO (pure Go)
OCaml runtime	YES (EC is OCaml)	NO	NO
Go toolchain	YES (Go reference)	YES (Go reference; primary)	YES (Go reference)
cloudflare/circl FIPS 205	NO (Pulsar uses FIPS 204)	YES (FIPS 205 single-party kernel)	NO (R-LWE; no FIPS standard)
luxfi/lattice/v7 (lattigo fork)	NO	NO	YES (R-LWE primitives)
crypto/subtle (or local CT helpers)	YES	YES (local ctEqualSlice / ctEqual32)	YES
golang.org/x/crypto/sha3	YES	YES	YES
NIST standard target	FIPS 204 ML-DSA	FIPS 205 SLH-DSA	none (Boschini ePrint 2024/1113)
Third-party FIPS-validated verifier available	YES (BoringSSL FIPS / AWS-LC / OpenSSL 3.0 ML-DSA)	PARTIAL (FIPS 205 still landing in third-party stacks at submission time)	NO (none exists for R-LWE threshold)

Net effect: Magnetar's TCB is smaller than Pulsar's (fewer proof-tool dependencies) but the trust per-component is higher (no fall-back to a mechanized refinement chain if a Go reviewer misses a bug in the threshold overlay). Compared to Corona, Magnetar has a STRONGER baseline because the single-party layer is FIPS-anchored (FIPS 205) while Corona's underlying construction is a 2024 academic paper with less cryptanalytic surface area.

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Document metadata

• Name: TRUSTED-COMPUTING-BASE.md
• Version: v0.1 (initial Tier A submission-package scaffolding)
• Date: 2026-05-18
• Go toolchain pin: see go.mod
• cloudflare/circl pin: see go.mod
• golang.org/x/crypto pin: see go.mod