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Add TaprootSpendData data structure, equivalent to script map for P2[W]SH

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This data structures stores all information necessary for spending a taproot
output (the internal key, the Merkle root, and the control blocks for every
script leaf).

It is added to signing providers, and populated by the tr() descriptor.
This commit is contained in:
Pieter Wuille
2021-03-03 15:02:56 -08:00
parent b0e5fbf6fa
commit dbb0ce9fbf
6 changed files with 109 additions and 7 deletions
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57
src/script/standard.cpp
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@@ -377,6 +377,16 @@ bool IsValidDestination(const CTxDestination& dest) {
/*static*/ TaprootBuilder::NodeInfo TaprootBuilder::Combine(NodeInfo&& a, NodeInfo&& b)
{
NodeInfo ret;
/* Iterate over all tracked leaves in a, add b's hash to their Merkle branch, and move them to ret. */
for (auto& leaf : a.leaves) {
leaf.merkle_branch.push_back(b.hash);
ret.leaves.emplace_back(std::move(leaf));
}
/* Iterate over all tracked leaves in b, add a's hash to their Merkle branch, and move them to ret. */
for (auto& leaf : b.leaves) {
leaf.merkle_branch.push_back(a.hash);
ret.leaves.emplace_back(std::move(leaf));
}
/* Lexicographically sort a and b's hash, and compute parent hash. */
if (a.hash < b.hash) {
ret.hash = (CHashWriter(HASHER_TAPBRANCH) << a.hash << b.hash).GetSHA256();
@@ -386,6 +396,21 @@ bool IsValidDestination(const CTxDestination& dest) {
return ret;
}
void TaprootSpendData::Merge(TaprootSpendData other)
{
// TODO: figure out how to better deal with conflicting information
// being merged.
if (internal_key.IsNull() && !other.internal_key.IsNull()) {
internal_key = other.internal_key;
}
if (merkle_root.IsNull() && !other.merkle_root.IsNull()) {
merkle_root = other.merkle_root;
}
for (auto& [key, control_blocks] : other.scripts) {
scripts[key].merge(std::move(control_blocks));
}
}
void TaprootBuilder::Insert(TaprootBuilder::NodeInfo&& node, int depth)
{
assert(depth >= 0 && (size_t)depth <= TAPROOT_CONTROL_MAX_NODE_COUNT);
@@ -435,13 +460,14 @@ void TaprootBuilder::Insert(TaprootBuilder::NodeInfo&& node, int depth)
return branch.size() == 0 || (branch.size() == 1 && branch[0]);
}
TaprootBuilder& TaprootBuilder::Add(int depth, const CScript& script, int leaf_version)
TaprootBuilder& TaprootBuilder::Add(int depth, const CScript& script, int leaf_version, bool track)
{
assert((leaf_version & ~TAPROOT_LEAF_MASK) == 0);
if (!IsValid()) return *this;
/* Construct NodeInfo object with leaf hash. */
/* Construct NodeInfo object with leaf hash and (if track is true) also leaf information. */
NodeInfo node;
node.hash = (CHashWriter{HASHER_TAPLEAF} << uint8_t(leaf_version) << script).GetSHA256();
if (track) node.leaves.emplace_back(LeafInfo{script, leaf_version, {}});
/* Insert into the branch. */
Insert(std::move(node), depth);
return *this;
@@ -464,8 +490,33 @@ TaprootBuilder& TaprootBuilder::Finalize(const XOnlyPubKey& internal_key)
m_internal_key = internal_key;
auto ret = m_internal_key.CreateTapTweak(m_branch.size() == 0 ? nullptr : &m_branch[0]->hash);
assert(ret.has_value());
std::tie(m_output_key, std::ignore) = *ret;
std::tie(m_output_key, m_parity) = *ret;
return *this;
}
WitnessV1Taproot TaprootBuilder::GetOutput() { return WitnessV1Taproot{m_output_key}; }
TaprootSpendData TaprootBuilder::GetSpendData() const
{
TaprootSpendData spd;
spd.merkle_root = m_branch.size() == 0 ? uint256() : m_branch[0]->hash;
spd.internal_key = m_internal_key;
if (m_branch.size()) {
// If any script paths exist, they have been combined into the root m_branch[0]
// by now. Compute the control block for each of its tracked leaves, and put them in
// spd.scripts.
for (const auto& leaf : m_branch[0]->leaves) {
std::vector<unsigned char> control_block;
control_block.resize(TAPROOT_CONTROL_BASE_SIZE + TAPROOT_CONTROL_NODE_SIZE * leaf.merkle_branch.size());
control_block[0] = leaf.leaf_version | (m_parity ? 1 : 0);
std::copy(m_internal_key.begin(), m_internal_key.end(), control_block.begin() + 1);
if (leaf.merkle_branch.size()) {
std::copy(leaf.merkle_branch[0].begin(),
leaf.merkle_branch[0].begin() + TAPROOT_CONTROL_NODE_SIZE * leaf.merkle_branch.size(),
control_block.begin() + TAPROOT_CONTROL_BASE_SIZE);
}
spd.scripts[{leaf.script, leaf.leaf_version}].insert(std::move(control_block));
}
}
return spd;
}