Files
proofs/lean/Crypto/MLKEM.lean
zooqueenandHanzo Dev d3bff5e2dc proofs: drive Lean library to 0 errors, eliminate proof-by-assumption axioms
The lean/ proof library (88 files) had ~180 type-check errors across ~45 files
plus 31 proof-by-assumption axiom cheats. It now type-checks cleanly under
Lean 4.14.0 + Mathlib, with every theorem genuinely proven from definitions.

Errors fixed:
- Stale Mathlib imports: Data.Nat.Basic / Data.Int.Basic were removed this rev
  -> Data.Nat.Defs / Data.Int.Defs (57 files).
- Shared AI/Agent/Governance/Contract/DeFi/Ecology draft files: same proof-rot
  as the zoo-labs sibling library (now reconciled): omega missing in-scope
  bounds, dead tactics after simp, simp over-reduction, doc-comment placement,
  reserved-word binders, deriving Repr on Finset-bearing structs, noncomputable
  defs over opaque primitives.
- Consensus/Liveness: collapsed a 74-error cascade (undefined shared state model
  inlined from Safety.lean; the |>. pipe-projection vs comparison parse trap on
  14 lines rewritten to explicit dot projection).
- Crypto (BLS/FROST/Corona/Hybrid/threshold/FHE), Consensus, Protocol, Warp,
  Trust, GPU, Compute, Network, DeFi: brought structure invariants into scope
  for omega, Nat-division bounds via Nat.div_le_of_le_mul / Nat.div_mul_le_self,
  noncomputable over opaque crypto ops, deriving Inhabited for index access.

Integrity:
- Removed all 31 `theorem X := X_ax` cheats (axiom asserting the identical
  statement) and proved each from definitions; removed the UNSOUND
  content_addressed axiom (hash-injectivity over a struct with free fields).
- Quorum-intersection theorems (BFT/Quasar/Flare/Warp/BLS/GPU/Bridge): the draft
  hypothesis 3f<n is insufficient (n unbounded above makes them false); tightened
  to the optimal-resilience invariant n=3f+1 / 2t>n. Statement intent preserved.
- Net axiom change: -35 / +1 (the one addition, honesty_static, is a
  fixed-validator-set modeling assumption matching sibling files).
- Remaining axioms are trusted-base only: opaque crypto primitives (groups,
  pairings, hardness, hashes, FHE encrypt/decrypt, BLS soundness, forward
  secrecy, Fisher-Yates uniformity) and protocol modeling assumptions. No
  sorry/admit/native_decide. Verified all theorems trace to
  [propext, Classical.choice, Quot.sound] plus those primitives.

Co-authored-by: Hanzo Dev <[email protected]>
2026-06-02 05:54:28 -07:00

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/-
Authors: Antje Worring, Zach Kelling
ML-KEM (FIPS 203) Key Encapsulation Correctness
Post-quantum key encapsulation mechanism. Used for key exchange
in the hybrid handshake protocol.
Based on CRYSTALS-Kyber (Module-LWE).
Maps to:
- luxfi/crypto: mlkem package
- lux/node: post-quantum key exchange in SSP handshake
- Quasar consensus: quantum-safe channel establishment
Properties:
- Correctness: decaps(encaps(pk)) recovers the shared secret
- IND-CCA2 security under Module-LWE
- Key sizes by security level
-/
import Mathlib.Data.Nat.Defs
import Mathlib.Tactic
namespace Crypto.MLKEM
/-- ML-KEM security levels (FIPS 203) -/
inductive SecurityLevel where
| mlkem512 -- NIST Level 1 (128-bit)
| mlkem768 -- NIST Level 3 (192-bit) ← default for Lux
| mlkem1024 -- NIST Level 5 (256-bit)
deriving DecidableEq, Repr
/-- Public key sizes (bytes) -/
def pkSize : SecurityLevel → Nat
| .mlkem512 => 800
| .mlkem768 => 1184
| .mlkem1024 => 1568
/-- Secret key sizes (bytes) -/
def skSize : SecurityLevel → Nat
| .mlkem512 => 1632
| .mlkem768 => 2400
| .mlkem1024 => 3168
/-- Ciphertext sizes (bytes) -/
def ctSize : SecurityLevel → Nat
| .mlkem512 => 768
| .mlkem768 => 1088
| .mlkem1024 => 1568
/-- Shared secret size (always 32 bytes) -/
def ssSize : SecurityLevel → Nat
| _ => 32
/-- Key generation -/
axiom keygen : SecurityLevel → Nat × Nat -- (pk, sk)
/-- Encapsulation: pk → (ct, ss) -/
axiom encaps : SecurityLevel → Nat → Nat × Nat
/-- Decapsulation: sk → ct → ss -/
axiom decaps : SecurityLevel → Nat → Nat → Nat
/-- Correctness: decaps(sk, encaps(pk).ct) = encaps(pk).ss
for matching (pk, sk) keypair -/
axiom mlkem_correctness :
∀ (level : SecurityLevel),
let (pk, sk) := keygen level
let (ct, ss) := encaps level pk
decaps level sk ct = ss
/-- IND-CCA2 security: ciphertexts are indistinguishable
under Module-LWE hardness assumption -/
axiom mlkem_ind_cca2 :
∀ (level : SecurityLevel) (pk : Nat) (ss0 ss1 : Nat),
-- No PPT/quantum adversary can distinguish encapsulations
-- of ss0 vs ss1 with non-negligible advantage
True
/-- Shared secret is always 32 bytes -/
theorem ss_fixed_size (level : SecurityLevel) : ssSize level = 32 := by
cases level <;> rfl
/-- ML-KEM-768 is the default for Lux (NIST Level 3) -/
theorem default_level_3 : pkSize .mlkem768 = 1184 := rfl
/-- Key sizes grow with security level -/
theorem pk_monotone_512_768 : pkSize .mlkem512 < pkSize .mlkem768 := by
simp [pkSize]
theorem pk_monotone_768_1024 : pkSize .mlkem768 < pkSize .mlkem1024 := by
simp [pkSize]
/-- Ciphertext size is bounded -/
theorem ct_bounded (level : SecurityLevel) : ctSize level ≤ 1568 := by
cases level <;> simp [ctSize]
/-- Combined hybrid KEM: ML-KEM + X25519 for belt-and-suspenders -/
axiom hybrid_kem_ss : SecurityLevel → Nat → Nat → Nat
/-- Hybrid KEM: shared secret combines both KEMs -/
axiom hybrid_kem_combines_both :
∀ (level : SecurityLevel) (mlkem_ss x25519_ss : Nat),
-- The hybrid shared secret is derived from BOTH components
-- Breaking requires breaking BOTH ML-KEM AND X25519
hybrid_kem_ss level mlkem_ss x25519_ss ≠ mlkem_ss ∨
hybrid_kem_ss level mlkem_ss x25519_ss ≠ x25519_ss
end Crypto.MLKEM