risc0-ed25519-verified/TRUSTED-BASE.md

Trusted base

What you must believe for the theorems in this repository to transfer to the running Rust code. Everything else is machine-checked.

1. Lean 4 kernel (v4.30.0-rc2) and its three foundational axioms [propext, Classical.choice, Quot.sound]. Every certificate is #print axioms-audited against exactly this list.

2. mathlib (prebuilt oleans fetched by lake exe cache get).

3. Charon + Aeneas (pinned 9dd7f23c / bf13c42e): the translation from Rust MIR to the Lean model is assumed faithful. The generated gen/ files are never edited (comments only); proofs are stated ABOUT them.

4. External-function models (gen/*/FunsExternal.lean): Rust items that Aeneas cannot translate (constant-time subtle primitives, iterator plumbing, formatting) are axiomatized as opaque symbols. The axiom audit proves none of these axioms enters the dependency cone of any certificate, except where a model is explicitly listed below.

5. The signature-apex boundary (signature layer only): FOUR apex-tier certificates — CurveFieldProofs.verify_accepts_iff (byte apex: accepted iff compress([s]·B − [k]·A) = R byte-for-byte), verify_accepts_iff_point (half-lift: R is the canonical encoding of the recomputed point), verify_accepts_iff_point_eq (point equation: canonically-encoded Q accepted iff Q equals the recomputed point), and verify_accepts_iff_decompress (full lift: R decompresses to a valid on-curve point that equals the recomputed point) — are each #print axioms-audited by check.sh Phase 3b against EXACTLY the standard three plus this documented set, and the build fails on any deviation: ed25519.Signature (wire-format type), the single SHA-512 oracle verifying.sha512_hash3 (semantically Sha512(R ‖ A ‖ msg)), ed25519.Signature.to_bytes, and signature.error.Error/Error.new (opaque error type). The hash is an oracle with no algebraic properties assumed — the theorems hold for whatever bytes it produces; the SHA-512 implementation itself is NOT verified. Zero curve, scalar, or backend axioms are in any of the four cones. The constructive decompress theorem underneath the full lift (decompress_of_canonical) carries the standard three axioms ONLY.

6. Scalar52::sub::black_box (scalar layer): this fork's v4.1.3 code implements the constant-time conditional via a local black_box = unsafe { core::ptr::read_volatile(&value) }. The volatile read is an optimization fence whose VALUE semantics is the identity; it is modeled as id in gen/CurveField/FunsExternal.lean (merged gen). (Upstream v5 uses subtle here; betrusted v4.1.2 uses a pure arithmetic mask — each fork is verified against its own strategy.)

7. Compilation of Rust to machine code (rustc backend) is out of scope, as is side-channel behaviour (timing, speculation). The proofs are about functional correctness at the MIR/LLBC level.

8. What the axiom gate binds, and what it does not. check.sh Phase 2b reads every compiled Proofs/*.olean and fails the build if any declaration there is an axiom. It asks the kernel rather than parsing source text, because the source-text check in Phase 1 is evadable four ways — an indented axiom, @[simp] axiom, unsafe axiom, and axiom with the name on the following line all compile and all miss its pattern. Membership self-derives from the filesystem, so Scalar* and AxiomCheck are covered as well, and the count of compiled modules must equal the count of shipped sources, so a deleted .olean cannot make the scan pass vacuously. selftest-axgate.sh attacks the shipping gate rather than a copy of it, and was itself negative-tested by removing the gate's error. The residue you must still supply yourself: this binds declarations, not statements. Nothing in the button establishes that a certificate's theorem says what its name — or this document — suggests it says. A theorem gutted to a tautology with the same axiom cone would pass every phase. Reading the statements remains a human act.

9. What the statement binding covers. check.sh Phase 3c compiles Proofs/Audit.lean, which emits a canonical block containing the policy constants, every certificate's fully-elaborated statement (pp.all, so implicit arguments, instances and universe levels are all visible), and the fully-elaborated body of every specification constant transitively reachable from those statements. The SHA-256 of that block is pinned in check.sh and the block itself is committed as AUDIT-MANIFEST.txt, so a mismatch is diffed rather than merely reported. This is what makes a certificate gutted to a tautology of the same axiom cone fail, and what makes a reference definition redefined to BE the extracted code fail — two attacks that move no cone at all. Phase 0b separately pins the bytes of every extracted-model file under gen/, with membership derived from the filesystem so a new model file fails closed.

   The residue you must still supply yourself. Three things, stated plainly because a reader would otherwise assume them:

   · A digest binds identity, not meaning. The audit proves the statements are the ones that were reviewed. Whether those statements say something worth believing about ed25519 is a question only a human reading them answers. AUDIT-MANIFEST.txt is committed precisely so that reading is possible without re-running anything.

   · An author can rotate the pins. Editing a statement and refreshing the digest in the same commit passes every phase. The defence is that both changes are visible in the diff, reviewed at the pinned commit — not that the script prevents it. No harness audits its own author.

   · Phase 0b pins the model; it does not verify the translation. That the bytes under gen/ are the reviewed bytes says nothing about whether Charon and Aeneas translated the Rust faithfully. That assumption is item 3 above and is unchanged.

10. The harness is pinned, and what that is worth. check.sh Phase 0c requires every executable file under verification/ — plus the audit driver, the committed manifests and the policy tables, which are not executable and are therefore listed explicitly in the script — to match HARNESS.sha256. Membership is derived from the executable bit, so a new script fails the build until someone pins it deliberately, and the required set is computed from the filesystem rather than read out of the pin file, so deleting an entry is a failure rather than a silent un-pinning. lean-guard is inside that set: stubbing the memory-capped compiler wrapper is the cheapest known route to a false green, demonstrated elsewhere in this estate as ALL GREEN in 3.6 seconds over deliberately destroyed proofs. selftest-harness.sh replays that attack and four others.

What it does NOT buy, stated plainly. Pinning a harness from inside that harness is circular, and no amount of engineering removes the circularity. An author who edits check.sh — or lean-guard, or the audit driver — and refreshes its pin in the SAME commit passes every phase. What the pin changes is that the edit can no longer be silent: it must appear in the diff, at the commit you are reviewing. That is why the consumer's protection is, and has always been, review at the pinned commit rather than the button's own verdict. A green button says "this is the apparatus that was reviewed", never "this apparatus is trustworthy".