mirror of
https://github.com/luxfi/magnetar.git
synced 2026-07-27 02:53:47 +00:00
Antje Worring
df4c537c16
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.
84 lines
3.8 KiB
Markdown
84 lines
3.8 KiB
Markdown
# Magnetar THBS-SE Combine: what the assemble path actually does
|
|
|
|
This document used to be the "load-bearing prose statement of the
|
|
strict-atom discipline that closes MAGNETAR-STRICT-ATOM-V11". That
|
|
framing was wrong. MAGNETAR-STRICT-ATOM-V11 is **NOT closed** (see
|
|
`BLOCKERS.md`). This document now states plainly what
|
|
`ref/go/pkg/magnetar/thbsse_assemble.go` does.
|
|
|
|
## The fact
|
|
|
|
`assembleSignatureBytes` RECONSTRUCTS the full FIPS 205 master at the
|
|
public combiner, every signature:
|
|
|
|
1. It Lagrange-interpolates the t share envelopes byte-by-byte into a
|
|
buffer `derivedExpandInput`.
|
|
2. It SHAKE-expands that into a single buffer `derivedMaterial`
|
|
= `skSeed || skPrf || pkSeed` (FIPS 205 §10.1).
|
|
3. It drives a FIPS 205 §5--§8 signing walk that reads positional
|
|
slices of `derivedMaterial` (the §5/§6/§7/§8 PRF input and the
|
|
§11.2 PRF_msg key).
|
|
|
|
For the duration of one Sign call, the entire private key is resident
|
|
in the combiner's process memory. The combiner is PUBLIC (any peer can
|
|
run it), so this is a reconstruction at an untrusted party.
|
|
|
|
## The "strict-atom" naming convention is not a security property
|
|
|
|
The earlier revision avoided the identifier `seed` (and `skSeed`,
|
|
`skPrf`, ...) and routed access through closures over positional
|
|
slices of `derivedMaterial`. It then claimed this "secures" something
|
|
that a `seed []byte` local did not, and called it a discipline that
|
|
"closes" the no-leak gap.
|
|
|
|
That is false. Renaming the buffer changes the spelling, not the data.
|
|
`derivedMaterial` holds `skSeed || skPrf || pkSeed` exactly as a
|
|
variable named `seed` would. A memory-disclosure adversary (coredump,
|
|
`/proc/self/mem`, a compromised combiner process) observes the master
|
|
during the Sign call either way. There is no confidentiality property
|
|
to rely on, and the "strict-atom invariant" buys none.
|
|
|
|
This is a fundamental property of hash-based signatures, not a fixable
|
|
implementation detail: there is no algebraic structure to aggregate,
|
|
so producing one FIPS 205-shaped signature from shares requires either
|
|
reconstructing the seed at some party (this path) or full MPC over the
|
|
SHAKE hash tree (open research; multi-second, multi-megabyte per
|
|
signature). See `standalone.go`'s banner for the literature
|
|
(Cozzo-Smart 2019, Bonte-Smart-Tan 2023, NIST IR 8214).
|
|
|
|
## What the path actually gives
|
|
|
|
ONE property, and it is a CORRECTNESS/INTEROP property, not a
|
|
confidentiality one:
|
|
|
|
> The emitted signature is byte-identical to
|
|
> `circl/slhdsa.SignDeterministic` on the reconstructed master, so any
|
|
> unmodified FIPS 205 verifier accepts it.
|
|
|
|
Pinned by `TestSlhdsaInternal_ByteEqualToCirclSign` and
|
|
`TestThbsSE_StrictAtom_Combine_ByteIdentityToCircl`.
|
|
|
|
The scratch buffers (`prfAbsorb`, `prfMsgAbsorb`) and the derived
|
|
buffers (`derivedExpandInput`, `derivedMaterial`) are zeroized after
|
|
use. That is defense-in-depth against lingering heap copies, NOT a
|
|
guarantee the master was never resident — it was.
|
|
|
|
## Deployment positioning (see BLOCKERS.md and the product decision)
|
|
|
|
- **Permissionless THBS-SE (this path): RESEARCH-GRADE.** Master is
|
|
reconstructed at an untrusted public combiner. Do not present as
|
|
production or as "no host in the TCB at sign time".
|
|
- **Production default:** per-validator standalone (`standalone.go`) —
|
|
N independent FIPS 205 signatures, no reconstruction anywhere.
|
|
- **Opt-in trusted-hardware:** the TEE-attested combiner pool in
|
|
`luxfi/threshold/protocols/slhdsa-tee`. That relocates the
|
|
reconstruction into a measured enclave; it ADDS a host to the TCB
|
|
(trust-relocation), it is not MPC.
|
|
|
|
## The lint
|
|
|
|
`TestThbsSE_AssembleIdentHygiene` (Go) and `scripts/checks/strict-atom-ast.sh`
|
|
are an IDENTIFIER-HYGIENE LINT over `thbsse_assemble.go`. They assert
|
|
no variable is *spelled* `seed`/`skSeed`/... . That is a style/naming
|
|
check. It is not, and does not claim to be, a no-leak proof.
|