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saymrwulf
1766544daf
sub_val_spec closes the top-level two-clause value spec: denote(Scalar52.sub a b) = denote(a) - denote(b) in ZMod l for limb-bounded inputs with canonical subtrahend (scVal b < l). Axiom-clean [propext, Classical.choice, Quot.sound]; no sorry. The assembly documented-as-remaining last session is now done. Key resolutions: - Applied the WP "spec_bind" rule manually instead of "step", and reduced the resulting "let (difference,borrow) := (dw,w)" Prod-let with an explicit "show" — this was the destructuring friction that blocked the earlier attempt (step's arity heuristics mis-typed the pair result). - Inlined the subtle "Choice::from" identity (no step-spec, like csel_step). - PERFORMANCE: kept "scLimbs" as opaque atoms in the gamma5=1 derivation instead of "unfold ... at *" — the unfold exploded omega with 2^52..2^260 coefficients and blew past 600s; atomic form proves in ~1 min (METHOD 4, same kernel-cost discipline as the field layer). - The 2^260 borrow-wrap and the +l conditional-add cancel in ZMod l: beta5=0 direct; beta5=1 forces top carry gamma5=1 from scVal b < l, closed by linear_combination over the two telescopes (sub_telescope, add_telescope). check-scalar.sh: sub_val_spec in the manifest + Phase-3 audit (4/4 clean); proof-phase caps raised to 600s/8192MB for the assembly; full button green. exponentiation.threshold raised to 300 for the 2^260 literal. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
73 lines
3.5 KiB
Markdown
73 lines
3.5 KiB
Markdown
# dalek-ed25519-verified
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Formal verification of the ed25519 implementation in **dalek-cryptography/curve25519-dalek (upstream, v5.0.0-rc.1)**, built as a
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coherent proof pyramid in Lean 4 via the Charon/Aeneas transpilation pipeline:
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```
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┌──────────────────────────────┐
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│ Signature (EdDSA verify) │ accepted ⇒ [8][S]B = [8]R + [8][k]A
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├──────────────────────────────┤
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│ Scalar arithmetic mod ℓ │ Scalar52 ops correct mod ℓ
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├──────────────────────────────┤
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│ Group law (twisted Edwards) │ point ops = complete addition law
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├──────────────────────────────┤
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│ Field 𝔽_p, p = 2²⁵⁵ − 19 │ FieldElement51 ops correct mod p
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└──────────────────────────────┘
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```
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Every layer states its theorems about the **actual Aeneas-transpiled Rust
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code** (never about a hand-written re-model), and every claim in the status
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table below is backed by a compiled proof plus an axiom audit of the named
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certificate. Files that do not compile under `verification/check.sh` are not
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in this repository.
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## Layer status
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| Layer | Certificate | Status | Axioms of certificate |
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|-------|-------------|--------|-----------------------|
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| Field 𝔽_p | `fieldImplementation` | ✅ proven | `[propext, Classical.choice, Quot.sound]` |
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| Group law (Edwards) | `edwardsImplementation` | ✅ proven | `[propext, Classical.choice, Quot.sound]` |
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| Scalar mod ℓ | `scalarImplementation` (planned; `sub_val_spec` ✅, `L_val`, loop specs proven) | 🔨 sub done · add/mul next | denotation + L=ℓ + FULL sub (⟦sub a b⟧=⟦a⟧−⟦b⟧ in ZMod ℓ) proven; add & Montgomery mul next |
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| Signature (EdDSA) | `verifyEquation` (planned) | ⏳ planned | — |
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Status legend: ✅ proven & axiom-audited · ⏳ in progress · ❌ not started.
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This table is updated only when `verification/check.sh` passes for the layer.
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## Source
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- **Upstream**: [dalek-cryptography/curve25519-dalek](https://github.com/dalek-cryptography/curve25519-dalek), commit `4cf8db2`
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- **Pinned/patched source**: [saymrwulf/curve25519-dalek-source](https://github.com/saymrwulf/curve25519-dalek-source), commit `135ed70`
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- **Patches**: minimal Aeneas-compatibility only (documented in the source repo)
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- Verified backend: `backend/serial/u64` (`FieldElement51`, `Scalar52`). SIMD/AVX backends are out of scope (marked opaque).
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## Toolchain (pinned)
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| Component | Version |
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|-----------|---------|
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| Aeneas | `bf13c42e` |
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| Charon | `9dd7f23c` |
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| Lean | `v4.30.0-rc2` |
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| OCaml | `5.3.0` |
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## Reproducing
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```bash
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source ~/aeneas-toolchain/env.sh
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cd verification
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./extract.sh # Rust → LLBC → Lean (regenerates gen/)
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./check.sh # compiles EVERY shipped file + axiom-audits EVERY certificate
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```
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The scalar layer has its own pair of buttons:
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```bash
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./extract-scalar.sh # regenerates gen/CurveScalar (Scalar52 limb arithmetic)
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./check-scalar.sh # compiles the scalar gen + the proven scalar foundation
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```
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## Trusted base
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See [TRUSTED-BASE.md](TRUSTED-BASE.md) for the complete list of assumptions
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(Lean kernel, mathlib, Charon/Aeneas semantics, external-function models,
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and — in the signature layer only — an opaque SHA-512 model).
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