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Merge #18780: validation: add const for minimum witness commitment size

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692f8307fc test: add test for witness commitment index (fanquake)
06442549f8 validation: Add minimum witness commitment size constant (fanquake)

Pull request description:

  16101de5f3: Per [BIP 141](https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki#Commitment_structure), the witness commitment structure is at least 38 bytes,
  OP_RETURN (0x6a) + 36 (0x24) + 4 byte header (0xaa21a9ed) + 32 byte
  SHA256 hash. It can be longer, however any additional data has no
  consensus meaning.

  54f8c48d6a: As per BIP 141, if there is more than 1 pubkey that matches the witness
  commitment structure, the one with the highest output index should be
  chosen. This adds a sanity check that we are doing that, which will fail
  if anyone tries to "optimize" GetWitnessCommitmentIndex() by returning
  early.

ACKs for top commit:
  MarcoFalke:
    ACK 692f8307fc 🌵
  jonatack:
    Code review ACK 692f830
  ajtowns:
    ACK 692f8307fc
  jnewbery:
    utACK 692f8307fc
  laanwj:
    ACK 692f8307fc

Tree-SHA512: 7af3fe4b8a52fea2cdd0aec95f7bb935351a77b73d934bc88d6625a3503311b2a062cba5190b2228f97caa76840db3889032d910fc8e318ca8e7810a8afbafa0
This commit is contained in:
fanquake 2020-04-30 18:06:51 +08:00
commit 64673b1037
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GPG key ID: 2EEB9F5CC09526C1
3 changed files with 45 additions and 2 deletions
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34
src/test/validation_block_tests.cpp
View file

@ -340,4 +340,38 @@ BOOST_AUTO_TEST_CASE(mempool_locks_reorg)
rpc_thread.join();
}
}
BOOST_AUTO_TEST_CASE(witness_commitment_index)
{
CScript pubKey;
pubKey << 1 << OP_TRUE;
auto ptemplate = BlockAssembler(*m_node.mempool, Params()).CreateNewBlock(pubKey);
CBlock pblock = ptemplate->block;
CTxOut witness;
witness.scriptPubKey.resize(MINIMUM_WITNESS_COMMITMENT);
witness.scriptPubKey[0] = OP_RETURN;
witness.scriptPubKey[1] = 0x24;
witness.scriptPubKey[2] = 0xaa;
witness.scriptPubKey[3] = 0x21;
witness.scriptPubKey[4] = 0xa9;
witness.scriptPubKey[5] = 0xed;
// A witness larger than the minimum size is still valid
CTxOut min_plus_one = witness;
min_plus_one.scriptPubKey.resize(MINIMUM_WITNESS_COMMITMENT + 1);
CTxOut invalid = witness;
invalid.scriptPubKey[0] = OP_VERIFY;
CMutableTransaction txCoinbase(*pblock.vtx[0]);
txCoinbase.vout.resize(4);
txCoinbase.vout[0] = witness;
txCoinbase.vout[1] = witness;
txCoinbase.vout[2] = min_plus_one;
txCoinbase.vout[3] = invalid;
pblock.vtx[0] = MakeTransactionRef(std::move(txCoinbase));
BOOST_CHECK_EQUAL(GetWitnessCommitmentIndex(pblock), 2);
}
BOOST_AUTO_TEST_SUITE_END()

11
src/validation.cpp
View file

@ -3386,7 +3386,14 @@ int GetWitnessCommitmentIndex(const CBlock& block)
int commitpos = -1;
if (!block.vtx.empty()) {
for (size_t o = 0; o < block.vtx[0]->vout.size(); o++) {
if (block.vtx[0]->vout[o].scriptPubKey.size() >= 38 && block.vtx[0]->vout[o].scriptPubKey[0] == OP_RETURN && block.vtx[0]->vout[o].scriptPubKey[1] == 0x24 && block.vtx[0]->vout[o].scriptPubKey[2] == 0xaa && block.vtx[0]->vout[o].scriptPubKey[3] == 0x21 && block.vtx[0]->vout[o].scriptPubKey[4] == 0xa9 && block.vtx[0]->vout[o].scriptPubKey[5] == 0xed) {
const CTxOut& vout = block.vtx[0]->vout[o];
if (vout.scriptPubKey.size() >= MINIMUM_WITNESS_COMMITMENT &&
vout.scriptPubKey[0] == OP_RETURN &&
vout.scriptPubKey[1] == 0x24 &&
vout.scriptPubKey[2] == 0xaa &&
vout.scriptPubKey[3] == 0x21 &&
vout.scriptPubKey[4] == 0xa9 &&
vout.scriptPubKey[5] == 0xed) {
commitpos = o;
}
}
@ -3417,7 +3424,7 @@ std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBloc
CHash256().Write(witnessroot.begin(), 32).Write(ret.data(), 32).Finalize(witnessroot.begin());
CTxOut out;
out.nValue = 0;
out.scriptPubKey.resize(38);
out.scriptPubKey.resize(MINIMUM_WITNESS_COMMITMENT);
out.scriptPubKey[0] = OP_RETURN;
out.scriptPubKey[1] = 0x24;
out.scriptPubKey[2] = 0xaa;

2
src/validation.h
View file

@ -92,6 +92,8 @@ static const unsigned int DEFAULT_CHECKLEVEL = 3;
// one 128MB block file + added 15% undo data = 147MB greater for a total of 545MB
// Setting the target to >= 550 MiB will make it likely we can respect the target.
static const uint64_t MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
/** Minimum size of a witness commitment structure. Defined in BIP 141. **/
static constexpr size_t MINIMUM_WITNESS_COMMITMENT{38};
struct BlockHasher
{