Model keccak256 opcode, unaligned calldata, and SHA-256 engine in executable semantics#1943
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Th0rgal wants to merge 20 commits into
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Model keccak256 opcode, unaligned calldata, and SHA-256 engine in executable semantics#1943Th0rgal wants to merge 20 commits into
Th0rgal wants to merge 20 commits into
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Surface declared raw-Yul storage writes in the modifies() write-set, flag computed-slot writes as untrackable, and treat fragment call mechanics as external interactions for CEI ordering and external-call detection.
…ntics Make evalExpr/evalExprWithHelpers evaluate Expr.keccak256 via the in-tree KeccakEngine over a word-aligned RuntimeState memory slice, instead of returning none (revert). Adds keccakMemorySlice/memorySliceBytesBE/wordToBytesBE helpers; updates evalExpr_keccak256 and the helper-surface equivalence case. No new axiom or sorry: reuses the CI-cross-checked kernel Keccak. Trust docs (AXIOMS.md, TRUST_ASSUMPTIONS.md) updated to record the word-aligned-access faithfulness assumption (keccak256_memory_slice_matches_evm). Builds green: SourceSemantics + 8 reverse-dependency importers + SphincsMinusVerifiers.
Pure-Lean, axiom-free SHA-256 over ByteArray (Sha256Engine.sha256), mirroring KeccakEngine's role: prerequisite for modeling the EVM SHA-256 precompile (0x02) in the executable source semantics with a computed 32-byte digest. Verified against reference vectors (empty, "abc", quick-brown-fox, and the 56-byte padding-boundary case). UInt32 wrapping matches spec add-mod-2^32.
calldataloadWord now returns the EVM-faithful byte-addressed 32-byte window for unaligned offsets (r != 0), composing the hi/lo words with big-endian zero-padding. Aligned reads (r = 0) reduce to the prior single-word behaviour exactly. Needed for the C13 auth-path sibling reads at 16-byte-strided offsets in the Merkle-climb correspondence.
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…pport # Conflicts: # Compiler/CompilationModel/Types.lean # Compiler/CompilationModel/Validation.lean # Compiler/CompilationModelFeatureTest.lean
…e-Yul review invariants ff6c9c0 swapped calldataloadWord's aligned/unaligned branches (r = 0 now selects the aligned word) but left calldataloadWord_lt_evmModulus expecting the old layout, breaking the build at FunctionBody.lean:1969. Both branches now reduce mod evmModulus, so each discharges via Nat.mod_lt. Also document two invariants raised in the PR #1943 review: - LogicalPurity: raw Yul is emitted verbatim, so the logicalAnd/logicalOr/ite operand-duplication predicate correctly returns false; fragment external calls are caught in Validation, not here. - SourceSemantics: the keccak256 arm must evaluate offset/size with evalExpr to stay definitionally equal to evalExpr, because exprTouchesUnsupportedHelperSurface treats keccak256 as a helper-surface leaf and evalExprWithHelpers_eq_evalExpr depends on it.
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Summary
Extends Verity's executable source semantics with the hash/calldata
primitives the SPHINCS- C13 accept-path refinement needs. Enables the
keccak accept path to be executed (and thus proved) rather than
reverting at the first hash.
keccak256(offset,size)modeled (SourceSemantics.lean): newkeccakMemorySlice/memorySliceBytesBE/wordToBytesBEhelpers and.keccak256arms inevalExpr/evalExprWithHelpers, wired to thein-tree
KeccakEngine. Previously the first keccak madeexecStmtrevert, making the accept subdomain provably unreachable.
calldataloadWord(Calldata.lean): EVM-faithfulbyte-addressed 32-byte window for unaligned offsets (
r != 0), composinghi/lo words big-endian with zero-padding. Aligned reads (
r = 0) reduceto the prior single-word behaviour exactly. Needed for C13 auth-path
sibling reads at 16-byte-strided offsets.
Compiler/Sha256/Engine.lean),FIPS 180-4, verified against reference vectors. Infrastructure only — the
SHA-256 precompile (0x02) is deliberately NOT wired into the interpreter
yet (word-keyed memory cannot faithfully represent SLH-DSA's 16-byte
precompile-input layout).
Trust docs (
AXIOMS.md/TRUST_ASSUMPTIONS.md) updated forkeccak256_memory_slice_matches_evm. No newsorry; keccak engine iscross-checked against the EVM engine.
Test plan
lake buildofSourceSemantics+ reverse-dep importers greenSphincsMinusVerifiersbuilds against this branchNote
Medium Risk
Changes core executable semantics and calldata/hash modeling used by proofs, plus validation/CEI behavior for raw Yul; trust assumptions on word-aligned keccak preimages are explicit but correctness-sensitive.
Overview
Executable source semantics now evaluates
Expr.keccak256via word-aligned memory slicing and the in-treeKeccakEngine(previously alwaysnone/revert). Helper-aware evaluation andSupportedSpecsurface scans treatkeccak256as supported and recurse into offset/size operands. Trust docs documentkeccak256_memory_slice_matches_evm.calldataloadWordis updated for EVM-faithful unaligned 32-byte reads (hi/lo composition); aligned reads stay behavior-identical. Proof tweaks inFunctionBody.leanfollow the new branches.New kernel-computable SHA-256 engine (
Compiler/Sha256/Engine.lean) with FIPS reference-vector tests, wired intoCompiler.leanbuild — not hooked into the source interpreter yet.Raw Yul validation gains AST scans for
call/staticcall/delegatecallso CEI, external-call detection, andmayContainExternalCallcatch under-declared mechanics;unsafeYulstops false positives in logical-purity checks. Feature tests cover raw-call CEI propagation.Reviewed by Cursor Bugbot for commit fc265c3. Bugbot is set up for automated code reviews on this repo. Configure here.