mirror of
https://github.com/saymrwulf/betrusted-ed25519-verified.git
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mrwulf
6120f9bb17
Transpile the Scalar52 limb backend (backend::serial::u64::scalar
add/sub/mul/square/montgomery_*) from Rust to Lean via Charon/Aeneas,
scoped at the function level to the iterator-free arithmetic core.
- verification/extract-scalar.sh: function-level Charon/Aeneas extraction
- verification/gen/CurveScalar/{Types,Funs}.lean: transpiled model (27 defs).
This fork (v4.1.2) implements Scalar52::sub's constant-time conditional add
with a pure arithmetic mask (constants::L[i] & underflow_mask), so the
extraction pulls in NO external functions or types (unlike v5 dalek, which
routes sub through subtle, and v4.1.3, which uses a local black_box).
- verification/gen/CurveScalar/{TypesExternal,FunsExternal}.lean: decl-free
stub modules kept so the check manifest is uniform across forks.
- verification/Proofs/ScalarDenote.lean: semantic foundation — Scalar52
denotation into ℤ/ℓℤ, limb-bound invariant, and L_val (the transpiled
constants::L denotes exactly the group order ℓ, kernel-checked).
- verification/check-scalar.sh: guarded compile of the gen modules plus the
denotation foundation.
check-scalar.sh passes: gen compiles; denotation + L = ℓ proven.
add/sub/mul remain in progress.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
65 lines
3.2 KiB
Markdown
65 lines
3.2 KiB
Markdown
# betrusted-ed25519-verified
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Formal verification of the ed25519 implementation in **betrusted-io/curve25519-dalek (Precursor/Xous fork, v4.1.2)**, 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` | 🔨 foundation | denotation + L=ℓ proven; add/sub/mul in progress |
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| Signature (EdDSA) | `verifyEquation` | ⏳ in progress | — |
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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**: [betrusted-io/curve25519-dalek](https://github.com/betrusted-io/curve25519-dalek), commit `16e087a`
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- **Pinned/patched source**: [saymrwulf/betrusted-curve25519-dalek-source](https://github.com/saymrwulf/betrusted-curve25519-dalek-source), commit `64ee8f0`
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- **Patches**: minimal Aeneas-compatibility only (documented in the source repo)
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- **Scope caveat**: this verifies the fork's pure-Rust `serial/u64` path. The Engine25519 hardware-accelerator path on Precursor is different code and is NOT covered by these proofs.
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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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## 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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