diff options
| -rw-r--r-- | bip-0114.mediawiki | 48 |
1 files changed, 43 insertions, 5 deletions
diff --git a/bip-0114.mediawiki b/bip-0114.mediawiki index f2a960e..2d16084 100644 --- a/bip-0114.mediawiki +++ b/bip-0114.mediawiki @@ -133,24 +133,33 @@ This BIP depends on [[bip-0141.mediawiki|BIP141]] and will be deployed by versio The idea of MAST originates from Russell O’Connor, Pieter Wuille, and [https://bitcointalk.org/index.php?topic=255145.msg2757327#msg2757327 Peter Todd]. == Reference Implementation == -https://github.com/jl2012/bitcoin/commit/f335cab76eb95d4f7754a718df201216a4975d8c +https://github.com/jl2012/bitcoin/tree/segwit_mast <source lang="cpp"> +//New rules apply if version byte is 1 and witness program size is 32 bytes if (witversion == 1) { if (program.size() == 32) { + + //Witness stack must have at least 3 items if (witness.stack.size() < 3) return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); - //Script: the last witness stack item + //Script is the last witness stack item scriptPubKey = CScript(witness.stack.back().begin(), witness.stack.back().end()); uint256 hashScriptPubKey; CHash256().Write(&scriptPubKey[0], scriptPubKey.size()).Finalize(hashScriptPubKey.begin()); - //Path: the second last witness stack item; size = 32N, 0 <= N < 33 + //Path is the second last witness stack item std::vector<unsigned char> pathdata = witness.stack.at(witness.stack.size() - 2); + + // Size of Path must be a multiple of 32 bytes (0 byte is allowed) if (pathdata.size() & 0x1F) return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); + + // Depth of the tree is size of Path divided by 32 unsigned int depth = pathdata.size() >> 5; + + // Maximum allowed depth is 32 if (depth > 32) return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); std::vector<uint256> path; @@ -158,33 +167,62 @@ if (witversion == 1) { for (unsigned int i = 0; i < depth; i++) memcpy(path[i].begin(), &pathdata[32 * i], 32); - //Position: the third last witness stack item; unsigned int with smallest possible value and no leading zero + //Position is the third last witness stack item std::vector<unsigned char> positiondata = witness.stack.at(witness.stack.size() - 3); + + //Position may have 4 bytes at most if (positiondata.size() > 4) return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); + uint32_t position = 0; + + //Position is an unsigned little-endian integer with no leading zero byte if (positiondata.size() > 0) { if (positiondata.back() == 0x00) return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); for (size_t i = 0; i != positiondata.size(); ++i) position |= static_cast<uint32_t>(positiondata[i]) << 8 * i; } + + //Position must not be larger than the maximum number of items allowed by the depth of tree if (depth < 32) { if (position >= (1U << depth)) return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); } + //Calculate the Merkle Root and compare with the witness program uint256 root = ComputeMerkleRootFromBranch(hashScriptPubKey, path, position); if (memcmp(root.begin(), &program[0], 32)) return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); + //Remaining stack items used for evaluation stack = std::vector<std::vector<unsigned char> >(witness.stack.begin(), witness.stack.end() - 3); - } else { + } + + else { + //Invalid if version byte is 1 but witness program size is not 32 bytes return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_WRONG_LENGTH); } } </source> +Copying from <code>src/consensus/merkle.cpp</code>: +<source lang="cpp"> +uint256 ComputeMerkleRootFromBranch(const uint256& leaf, const std::vector<uint256>& vMerkleBranch, uint32_t nIndex) { + uint256 hash = leaf; + for (std::vector<uint256>::const_iterator it = vMerkleBranch.begin(); it != vMerkleBranch.end(); ++it) { + if (nIndex & 1) { + hash = Hash(BEGIN(*it), END(*it), BEGIN(hash), END(hash)); + } else { + hash = Hash(BEGIN(hash), END(hash), BEGIN(*it), END(*it)); + } + nIndex >>= 1; + } + return hash; +} +</source> + + == References == *[[bip-0141.mediawiki|BIP141 Segregated Witness (Consensus layer)]] |