mirror of
https://github.com/saymrwulf/fips205-slhdsa-verified.git
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mrwulf
e3f68b2473
Two theorems, split into two files (METHOD-4 discipline — each proof a clean
unit). NB: an early single-file/bare-rfl attempt appeared to "OOM at the clamp",
but that memory pressure was a SYMPTOM of the runaway whnf diagnosed below, not
a real memory need — the fixed proofs compile in seconds at the default caps.
fips205.fors_inner_loop_eq (Proofs/ForsInnerSpec.lean): the extracted inner
Merkle auth-path loop for ONE FORS tree (fors_pk_from_sig_free_loop0_loop0)
equals the explicit auth-path fold — at level j set tree height j+1, test bit j
of THIS tree's leaf index indices[i], hash the current node with auth.tree[j] in
the bit order (even: node||auth[j]; odd: auth[j]||node), halving the tree index.
Structurally the XMSS auth-path loop, but the bit source is indices[i]>>j and the
loop returns the (adrs,node) pair. Cone: kernel-3 + verify_mono.oracle.h.
fips205.fors_outer_loop_eq (Proofs/ForsOuterSpec.lean): the extracted outer
per-tree loop (fors_pk_from_sig_free_loop0) equals the explicit K-tree fold — for
each tree i, compute the leaf with F at tree index (i<<a)+indices[i], run the
inner Merkle loop over the A levels, write the result to root[i]. Consumes the
inner loop as an opaque sub-call. Cone: kernel-3 + verify_mono.oracle.{f,h}
(F per leaf; H transitively through the inner loop).
Fidelity review at authorship (three-way, both loops): extracted bodies (gen
Funs.lean 893-933 inner, 954-985 outer) == Rust verify_mono.rs
fors_pk_from_sig_free (verbatim from upstream fors.rs, hash calls -> oracle) ==
FIPS 205 Algorithm 17, incl. the even/odd sibling order and the (i<<a)+indices[i]
leaf index.
Proof: the branched-Merkle recipe (XMSS) for the inner loop (by_cases on the
index bit, pair-bind matcher made concrete via bind_congr+rintro then full simp);
the HT straight-line recipe for the outer loop, adapted (bind_congr-peeled step
lemma + bind_congr x16 induction, both threading the inner-loop sub-call opaquely). loop_unfold_bind / u32_succ
/ fwd_succ / hnext reused verbatim from ChainSpec.
check.sh: PROOFS += ForsInnerSpec, ForsOuterSpec; CERTS += the two fors certs;
audit imports both; check.sh settings unchanged (400s/4096MB). ForsOuterSpec
compiles in 4.4s / 2.4GB after the fix below. check.sh green over ALL SIX
certificates with the axiom audit. README status -> FIVE certificates.
DIAGNOSIS NOTE (honesty): ForsOuterSpec's fors_outer_step first closed with a
bare `rfl`, which whnf'd the whole 16-bind body INCLUDING the inner-loop `loop`
term and hit a DETERMINISTIC 4M-heartbeat timeout (never actually passed — an
earlier "green" reading was a misread wrapper exit code; the real error was
hidden by check.sh piping per-file output to /dev/null). Fix: peel the 16 binds
with bind_congr so the closing rfl only sees the small loop-tail, and close the
post-pair-rintro tail with a full simp (the pair `let` won't iota via simp only).
This is the HtSpec straight-line recipe adapted for a body that nests a loop.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
171 lines
9.1 KiB
Markdown
171 lines
9.1 KiB
Markdown
# fips205-slhdsa-verified
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Machine-checked verification campaign for the **SLH-DSA (FIPS 205) verify
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path**, extracted from a pure-Rust implementation into Lean 4 via
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Charon/Aeneas — the same pipeline, discipline, and honesty rules as the
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four ed25519 campaigns (`dalek/anza/risc0/betrusted-ed25519-verified`).
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## STATUS: FIVE LAYERS PROVEN — chain (5), WOTS+ loop (8), XMSS (10), hypertree (12), FORS (17)
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`verification/check.sh` is **green** (exit 0): the model compiles, the
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proofs compile, and the axiom audit passes. **Six theorems across five
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verify-path layers, proven bottom-up:**
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- **`fips205.chain_free_loop_eq`** (Algorithm 5, WOTS+ chaining): the
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extracted `chain_free` loop equals the explicit s-fold hash chain, with
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the hash address set to i, i+1, …, i+s−1 in turn. This rules out —
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machine-checked, for the deployed monomorphic SHA2-128s verify path — an
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off-by-one loop bound, a wrong address field, and wrong threading. Its
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`#print axioms` cone is **exactly** `[propext, Classical.choice,
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Quot.sound, verify_mono.oracle.f]` — the three kernel axioms plus the one
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hash oracle it touches, and nothing else (no transpiler plumbing; the u32
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range machinery was discharged with real definitions). check.sh Phase 3
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fails the build if any certificate cone contains anything outside the
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kernel three + the five documented SHA-2 oracles.
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- **`fips205.wots_loop1_eq`** (Algorithm 8, WOTS+ pk recomputation — the
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chain loop): the extracted `wots_pk_from_sig_free_loop1` equals the fold
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that, at each index i in [0, LEN), sets the chain address to i and runs
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`chain_free` on sig[i] starting at digit msg[i] for W−1−msg[i] steps,
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writing tmp[i]. This is the layer above chain: it consumes `chain_free`
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and pins that the LEN chains run with the right start indices, step
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counts, and slots. Cone: kernel three + `verify_mono.oracle.f`.
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- **`fips205.xmss_loop_eq`** (Algorithm 10, XMSS pk-from-sig — the
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authentication-path Merkle loop): the extracted
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`xmss_pk_from_sig_free_loop` equals the fold that, at step k, sets the
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tree height to k+1, tests bit k of the leaf index, and on an even bit
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halves the tree index and hashes H(node ∥ auth[k]), on an odd bit sets
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the tree index to (i−1)/2 and hashes H(auth[k] ∥ node). This pins the
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Merkle sibling ORDER (the even/odd rule), the tree-height/tree-index
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address schedule, and the auth-path indexing — the heart of Merkle-path
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verification. Cone: kernel three + `verify_mono.oracle.h` (the first
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certificate where H enters; F does not — the loop runs above the WOTS+
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computation).
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- **`fips205.ht_loop_eq`** (Algorithm 12, hypertree verification — the
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layer walk): the extracted `ht_verify_free_loop` equals the fold that,
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at layer j, splits the tree index (idx_leaf = idx_tree mod 2^h' by
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mask+cast, then idx_tree >>= h'), sets the layer address to j and the
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tree address to the shifted index, and recomputes the node through
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`xmss_pk_from_sig` on the j-th XMSS signature. This pins the layer
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schedule of hypertree verification; the final node = pk_root comparison
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sits one bind above, in `ht_verify_free`, and belongs to the apex
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composition. Cone: kernel three + `verify_mono.oracle.{f, h, t_l}` —
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the full WOTS+/XMSS machinery referenced through the fold, and nothing
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else.
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Foundations behind this (2026-07-22/23): the Aeneas-compat patch (additive
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monomorphic verify module through a named oracle boundary; charon + aeneas
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exit 0); the u32 range-loop de-plumbing (faithful `Step` defs vs pinned
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rustc, axiom-clean); the 8-site source de-plumbing (snapshot commit
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`6f6a9d6`: `try_from`/`is_err`/`unwrap` on pre-masked values → plain
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casts, the WOTS+ checksum `iter().take()` + `&u32` Sub → an index loop —
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each site semantics-identical for every FIPS 205 parameter set, and the
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obsoleted transpiler axioms deleted from the external files); fidelity
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pinned by a differential test in the snapshot (valid / corrupted /
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wrong-message), re-run green after every source patch.
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- **`fips205.fors_inner_loop_eq`** + **`fips205.fors_outer_loop_eq`**
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(Algorithm 17, FORS pk-from-sig): a nested loop, split into two theorems.
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The inner one pins the auth-path Merkle fold for a single FORS tree (bit
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source `indices[i] >> j`, `H` in the even/odd sibling order) — cone
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kernel-3 + `oracle.h`. The outer one pins the K-tree fold: for each tree
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compute the leaf with `F` at index `(i<<a)+indices[i]`, run the inner
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Merkle loop, write `root[i]` — cone kernel-3 + `oracle.{f, h}`. Split into
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two files under the memory discipline; the outer step lemma closes by
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peeling its 16-bind body with `bind_congr` (a bare `rfl` there whnf-times-
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out over the nested inner `loop`).
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The remaining layers (the input-prep/digest-split composition and the apex)
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are not yet proven — the pyramid rises one certificate at a time, each
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audited to the same boundary.
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## Subject
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- Upstream: `integritychain/fips205` — pure-Rust FIPS 205 (final standard,
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2024-08-13), zero `unsafe`, `no_std`, const-generic parameterization,
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modules mirroring the FIPS 205 algorithm structure.
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- Pinned at upstream commit `30bac08580aa61f653e5436d1bbacb5ffac446c4`
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(2025-09-01), snapshotted with full history at
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`saymrwulf/fips205-source` (snapshot head `5dca0db`, whose single
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deviation from verbatim is the removal of upstream CI workflows,
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documented in that commit). Aeneas-compat patches will land in the
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snapshot repo as transparent, individually-justified commits — never
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upstream. **No affiliation with, and no changes proposed to, the
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upstream project.**
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- Parameter set: **SLH-DSA-SHA2-128s** first (the small-signature profile
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deployed in the firmware/code-signing lane). The architecture
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generalizes; each further parameter set is a separate claim (rigor
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invariant R2).
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## Scope
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**Verify path only.** The extraction cone, mirroring FIPS 205's own
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algorithm tree:
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```
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slh_verify -> slh_verify_internal
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-> fors_pk_from_sig
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-> ht_verify -> xmss_pk_from_sig -> wots_pk_from_sig -> chain
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```
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Key generation and signing are out of scope (trusted base), exactly as
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ed25519 signing was. The five verify-path hash oracles (`h_msg, f, h,
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t_l, t_len` — SHA-2 instantiations; `prf`/`prf_msg` are sign-side only
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and never enter the cone) are opaque external models with written
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justifications, kept outside every certificate's dependency cone
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(honesty invariant H4); their semantics are the standing SHA-2 oracle
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boundary documented in [TRUSTED-BASE.md](TRUSTED-BASE.md).
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## Gate-0 record (2026-07-22)
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Per TARGETS.md ("re-verify before use"), the subject was probed before
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this repository was created:
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- **Charon**: clean (`charon cargo --preset=aeneas`, roots at the verify
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cone, `sha2/sha3/zeroize/rand_core` opaque, features
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`slh_dsa_sha2_128s`) — LLBC produced, exit 0.
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- **Aeneas**: translated the entire const-generic verify cone to Lean
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definitions (`wots.chain` … `slh.slh_verify_internal` all generated),
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with exactly **one obstruction class** (3 unique errors): the
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`crate::hashers::Hashers` struct of plain **function pointers** cannot
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be translated.
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- **Phase 1 — DONE (2026-07-22)**: the Aeneas-compat patch landed in
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`fips205-source` (snapshot `2d89ee3`): an additive monomorphic SHA2-128s
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verify module (`src/verify_mono.rs`) whose hash suite is reached through
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named free functions in `verify_mono::oracle` (marked opaque at the
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Charon boundary) — the `sha512_*`-shim pattern. Two further compat
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refinements: the message-digest input M' passes as a single `&[u8]`
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(nested `&[&[u8]]` is untranslatable), and one `let-else` became the
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`is_err`/`unwrap` idiom. `verification/extract.sh` now re-derives the
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model from the mono root; charon + aeneas both exit 0, and
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`verification/check.sh` compiles the result. The generic paths and all
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twelve parameter sets are untouched (the only change to existing code is
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two lines wiring the module).
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## What will be claimed (when the button is green, not before)
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One theorem per layer, each a statement about the **extracted** functions
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(H3), compiled by `verification/check.sh` with a per-certificate
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`#print axioms` audit (H1): chain semantics, WOTS+ pk recomputation,
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XMSS path recomputation, hypertree acceptance, FORS pk recomputation,
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and the apex — `slh_verify_internal` accepts iff the recomputed
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hypertree root equals the pinned public-key root.
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**The allowed axiom set, stated precisely:** unlike the ed25519 field and
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scalar layers (whose cones are exactly `[propext, Classical.choice,
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Quot.sound]`), the hash oracles permeate *every* SLH-DSA layer — `chain`
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already calls `F`. So each certificate's cone may contain the three
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kernel axioms **plus at most the five named oracles**
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(`verify_mono.oracle.{h_msg, f, h, t_l, t_len}`) — and nothing else: the
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transpiler-plumbing axioms currently in `FunsExternal.lean` must be
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discharged before any certificate ships, and the audit fails the button
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if any of them (or anything unlisted) appears in a cone.
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## Discipline
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Every Lean compile in this repository runs under `verification/lean-guard`
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(memory-capped, machine-wide serialized). Extraction is reproducible from
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the committed `extract.sh` against the pinned snapshot (R1). What cannot
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be proven is named in [TRUSTED-BASE.md](TRUSTED-BASE.md), not hidden (H5).
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