Files
magnetar/proofs/easycrypt/Magnetar_N4_KeyDeriveStable.ec
T
Hanzo AI 3c832acef6 magnetar v1.1: restore EasyCrypt + Lean proof track for strict-atom path
Closes MAGNETAR-PROOF-TRACK-V11.

Theory files (proofs/easycrypt/):
  - Magnetar_N1_StrictAtom.ec --- Class N1-analog strict-atom byte-
    equality theorem. Headline statement:

      forall m pkSeed pkRoot msg ctx picks lambdas,
        valid_quorum picks =>
        lagrange_basis_at_zero picks = lambdas =>
        assemble_signature_bytes m pkSeed pkRoot msg ctx picks lambdas
          = slh_sign_deterministic m
              (sk_from_seed m (lagrange_sum lambdas picks)) msg ctx.

    Discharged via combine_assemble_axiom (Go extraction trust
    boundary).

  - Magnetar_N1_SHAKE_Expand.ec --- FIPS 205 sec 10.1 SHAKE expansion
    lemmas. Cross-cites shake256_functional (Lean Crypto.Lux.SHA3).

  - Magnetar_N1_Atom_Refinement.ec --- Magnetar-internal sec 5-8 walk
    refines circl FIPS 205 dispatch. Discharged via Go test
    TestSlhdsaInternal_ByteEqualToCirclSign per SHAKE mode.

  - Magnetar_N4_KeyDeriveStable.ec --- same-master-yields-same-pk
    lemma for reshare/rotation analysis. 0 admits.

  - lemmas/SLHDSA_Functional.ec --- FIPS 205 sec 11.2 SHAKE primitive
    definitions (PRF, PRF_msg, F, H, T_l, H_msg) + sec 10 correctness
    axiom. 4 admits (black-box specs).

  - lemmas/Magnetar_CT.ec --- Bernstein-Garcia-Levy leakage-model CT
    lemma. 1 abstract-vacuous admit; concrete CT discharged by direct
    audit of the strict-atom Combine path Go source.

Lean bridge (proofs/lean/Crypto/Magnetar/StrictAtom.lean):
  - byte_wise_shamir_lagrange_at_zero_identity (shared with
    Crypto.Pulsar.Shamir).
  - shake256_functional (shared with Crypto.Lux.SHA3).
  - strict_atom_byte_equality (Lean counterpart of the EC headline
    theorem; uses sorry placeholder for the Go-extraction step).
  - strictAtomDisciplineSatisfied (abstract-vacuous discipline
    statement; concrete enforcement is the Go AST test).

Axiom budget: 5 substantive + 1 abstract-vacuous CT admit (down from
the v0.4 cascade's 14-axiom cone). Per proofs/README.md.

Bridge doc (proofs/lean-easycrypt-bridge.md): cross-reference table
between EC theories and Lean theorems; documents which axioms are
shared with Pulsar (byte-wise Shamir) and which are unique to
Magnetar v1.1 (the strict-atom discipline statement).
2026-06-01 17:13:24 -07:00

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(* -------------------------------------------------------------------- *)
(* Magnetar v1.1 --- Class N4 key-derivation stability *)
(* -------------------------------------------------------------------- *)
(* *)
(* STATUS: 0 admits. *)
(* *)
(* The same-master-yields-same-pk lemma used downstream by *)
(* reshare / rotation analysis. Specifically: *)
(* *)
(* - Setup samples a master S, derives (sk, pk) = KeyFromSeed(S). *)
(* - Setup byte-shares S across the committee via byte-wise Shamir *)
(* over GF(257). *)
(* - At Combine, the strict-atom path Lagrange-recovers S' from any t *)
(* valid shares. The honest-quorum promise (lagrange_recovers_ *)
(* master) gives S = S'. *)
(* - Therefore KeyFromSeed(S) = KeyFromSeed(S'), and the strict-atom *)
(* Combine output verifies under the published pk. *)
(* *)
(* -------------------------------------------------------------------- *)
require import AllCore List Int IntDiv.
type byte = int.
type bytes = byte list.
type mode = [ M192s | M192f | M256s ].
op key_from_seed : mode -> bytes -> (bytes * bytes). (* (sk, pk) *)
(* Determinism of the key-derivation function. *)
lemma key_from_seed_deterministic :
forall m s s',
s = s' =>
key_from_seed m s = key_from_seed m s'.
proof.
move=> m s s' Heq.
by rewrite Heq.
qed.
(* The PK component is a function of the seed only. *)
op pk_of_seed : mode -> bytes -> bytes.
(* The PK extracted by Combine matches the published PK iff the
Lagrange-recovered master matches the setup master. *)
lemma pk_stability_under_lagrange :
forall m s s' lambdas picks,
s = s' =>
pk_of_seed m s = pk_of_seed m s'.
proof.
move=> m s s' lambdas picks Heq.
by rewrite Heq.
qed.