nmc(P1c): complete AuxPow::check_proof — all four merge-mining legs + parent-PoW gate - #185
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check_proof() reconstructs the merged-mining merkle root from the aux block hash through chain_merkle_branch/chain_merkle_index via the P1a aux_merkle_root() primitive. New INCOMPLETE CheckResult state: a structurally-consistent chain-merkle walk returns INCOMPLETE (never VALID) because step 2 (MM-marker commitment + chain_id/slot binding), step 3 (parent-coinbase tx-merkle leg) and step 4 (parent PoW) are not built yet -- NMC still MUST NOT block-validate off this leaf. Malformed slot indices (negative, or wider than branch depth) return INVALID. 4 KATs pin the INCOMPLETE-vs-INVALID boundary so the leg cannot silently regress into asserting VALID. nmc_coin linked into the test (AuxPow ctor pulls MutableTransaction). 9/9 PASS. NMC-local, btc tree READ-ONLY.
…p 3) + witness-stripped txid KAT Adds nmc::coin::parent_coinbase_txid() (Hash over TX_NO_WITNESS serialization, byte-identical to btc compute_txid() but NMC-local per the coin fence) and wires AuxPow::check_proof step 3: reconstruct the parent block tx-merkle-root from the witness-stripped coinbase txid through parent_coinbase_branch/index via aux_merkle_root(). When a parent header is present the reconstructed root MUST equal parent_header.m_merkle_root, else INVALID; malformed legs (negative index, index wider than branch depth) are INVALID. Steps 2 (MM-marker commitment) and 4 (parent PoW) remain unbuilt, so a structurally-consistent proof still returns INCOMPLETE, never VALID -- NMC MUST NOT block-validate off this leaf. The load-bearing KAT asserts the exact byte serialization: the txid is hashed over the LEGACY (no-witness) layout -- txid, NOT wtxid -- re-derived field-by- field without SerializeTransaction's witness/marker path, and is shown to differ from the wtxid for a coinbase carrying the BIP141 reserved value. Plus 4 check_proof boundary KATs (match=>INCOMPLETE, mismatch/negative/too-wide=> INVALID). nmc_auxpow_merkle_test 14/14 PASS exit 0. NMC-local, btc tree READ-ONLY, test target name unchanged (CI allowlist untouched).
…_id/slot binding
Step 2 of AuxPow verification: confirm the chain-merkle root reconstructed in
step 1 is the one committed inside the parent (BTC) coinbase merged-mining
marker, and that this aux chain occupies the deterministic slot its
(nonce, chain_id) demands.
NMC-local port of Namecoin/Bitcoin auxpow.cpp CAuxPow::check coinbase scan
(coin fence: only std + core/* types, no btc include):
* scan_mm_commitment(): the 4-byte pchMergedMiningHeader (fa be 6d 6d) must
appear exactly once; the chain-merkle root must follow it immediately in
reversed (big-endian display) byte order; the next LE uint32 tree size must
equal 2^height; the following LE uint32 nonce must place the chain at
chain_index == aux_expected_index(nonce, chain_id, height).
* aux_expected_index(): byte-faithful CAuxPow::getExpectedIndex LCG.
Staged posture preserved: a coinbase carrying no marker (leg-only fixture or
empty parent coinbase) returns ABSENT -> step 2 skipped, mirroring the
null-parent-header gate in step 3. A marker that commits a different root,
wrong tree size, wrong slot, or is duplicated -> INVALID. The proof still never
reaches VALID -- step 4 (parent PoW vs target, btc tree READ-ONLY) is unbuilt,
so a structurally-consistent proof stays INCOMPLETE and NMC MUST NOT
block-validate off this leaf.
KATs: aux_expected_index pinned to offline-computed LCG values; the committed
root laid out by hand (magic|reversed-root|LE size|LE nonce) without calling
scan_mm_commitment, so a parse/scan bug is caught not mirrored.
nmc_auxpow_merkle_test 22/22 PASS exit 0 (was 14/14, +8).
…ep 4) Complete the four-leg AuxPow verification walk: verify the parent (BTC) block proof-of-work. Per Namecoin CheckAuxPowProofOfWork the parent block SHA256d hash must satisfy the AUX (NMC) block difficulty target, NOT the parent header own nBits, so check_proof() gains a uint32_t aux_bits param (default 0). The PoW gate fires only with a real parent header and a non-zero aux_bits: pow_hash(parent_header) > bits_to_target(aux_bits) is INVALID (parent has insufficient work); otherwise the leg passes. With all four legs satisfied -- chain-merkle, MM-marker (matched), parent-coinbase tx-merkle, and parent PoW -- against a real parent header, check_proof() now finally returns VALID. Anything short (null parent, no matched marker, or aux_bits unset) stays INCOMPLETE so NMC never block-validates off a partial proof; aux_bits == 0 is the leg-only-fixture sentinel that preserves the staged posture. No btc-tree dependency: chain::bits_to_target lives in src/core and the PoW hash is the nmc-local pow_hash(); src/impl/btc is referenced read-only only. NMC-local per fence #4. +4 KATs (sufficient->VALID, insufficient->INVALID, no-aux_bits->INCOMPLETE, parent-own-bits-are-not-the-gate); the VALID KATs mine the parent nonce against an easy target so the success path is deterministic. nmc_auxpow_merkle_test 26/26 PASS exit 0.
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Summary
Completes
nmc::coin::AuxPow::check_proof()— promotes it from the P0-DEFER stub to a full merge-mining proof verifier. Builds on the merkle-walk primitive landed in #178 (@417b20af).Four legs now wired (one commit per step, KAT per step):
aux_merkle_root(); reconstructs the merged-mining root from (aux_block_hash, chain branch, chain index).aux_bitsexpanded via sharedchain::bits_to_target); the parents OWN bits are explicitly NOT the gate (KATParentOwnBitsAreNotTheAuxGate).A proof is VALID only when all legs pass: structural merkle reconstruction + matched MM marker + real parent header + parent PoW clearing the aux target. Anything short stays INCOMPLETE (fail-closed).
aux_bits == 0is the leg-only-fixture sentinel.Test
nmc_auxpow_merkle_test— 26/26 PASS (NmcAuxMerkle 5, NmcAuxCheckProof 4, NmcAuxParentCoinbase, NmcAuxStep2 7, NmcAuxStep4 4). Build green:nmc_coin,nmc_auxpow_merkle_testtargets.Scope
NMC-only (
src/impl/nmc/). No btc-tree changes. DOGE-under-LTC analog (M3). Merge operator/integrator-gated — I do not self-merge.