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Abstract out ComputeTapbranchHash

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This commit is contained in:
Russell O'Connor 2022-08-19 11:59:18 -04:00
parent 8e3fc99427
commit dee89438b8
4 changed files with 24 additions and 14 deletions
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19
src/script/interpreter.cpp
View File

@ -1830,6 +1830,17 @@ uint256 ComputeTapleafHash(uint8_t leaf_version, Span<const unsigned char> scrip
return (HashWriter{HASHER_TAPLEAF} << leaf_version << CompactSizeWriter(script.size()) << script).GetSHA256();
}
uint256 ComputeTapbranchHash(Span<const unsigned char> a, Span<const unsigned char> b)
{
HashWriter ss_branch{HASHER_TAPBRANCH};
if (std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end())) {
ss_branch << a << b;
} else {
ss_branch << b << a;
}
return ss_branch.GetSHA256();
}
uint256 ComputeTaprootMerkleRoot(Span<const unsigned char> control, const uint256& tapleaf_hash)
{
assert(control.size() >= TAPROOT_CONTROL_BASE_SIZE);
@ -1839,14 +1850,8 @@ uint256 ComputeTaprootMerkleRoot(Span<const unsigned char> control, const uint25
const int path_len = (control.size() - TAPROOT_CONTROL_BASE_SIZE) / TAPROOT_CONTROL_NODE_SIZE;
uint256 k = tapleaf_hash;
for (int i = 0; i < path_len; ++i) {
HashWriter ss_branch{HASHER_TAPBRANCH};
Span node{Span{control}.subspan(TAPROOT_CONTROL_BASE_SIZE + TAPROOT_CONTROL_NODE_SIZE * i, TAPROOT_CONTROL_NODE_SIZE)};
if (std::lexicographical_compare(k.begin(), k.end(), node.begin(), node.end())) {
ss_branch << k << node;
} else {
ss_branch << node << k;
}
k = ss_branch.GetSHA256();
k = ComputeTapbranchHash(k, node);
}
return k;
}

3
src/script/interpreter.h
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@ -334,6 +334,9 @@ public:
/** Compute the BIP341 tapleaf hash from leaf version & script. */
uint256 ComputeTapleafHash(uint8_t leaf_version, Span<const unsigned char> script);
/** Compute the BIP341 tapbranch hash from two branches.
* Spans must be 32 bytes each. */
uint256 ComputeTapbranchHash(Span<const unsigned char> a, Span<const unsigned char> b);
/** Compute the BIP341 taproot script tree Merkle root from control block and leaf hash.
* Requires control block to have valid length (33 + k*32, with k in {0,1,..,128}). */
uint256 ComputeTaprootMerkleRoot(Span<const unsigned char> control, const uint256& tapleaf_hash);

9
src/script/standard.cpp
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@ -370,12 +370,7 @@ bool IsValidDestination(const CTxDestination& dest) {
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 = (HashWriter{HASHER_TAPBRANCH} << a.hash << b.hash).GetSHA256();
} else {
ret.hash = (HashWriter{HASHER_TAPBRANCH} << b.hash << a.hash).GetSHA256();
}
ret.hash = ComputeTapbranchHash(a.hash, b.hash);
return ret;
}
@ -607,7 +602,7 @@ std::optional<std::vector<std::tuple<int, std::vector<unsigned char>, int>>> Inf
node.done = true;
stack.pop_back();
} else if (node.sub[0]->done && !node.sub[1]->done && !node.sub[1]->explored && !node.sub[1]->hash.IsNull() &&
(HashWriter{HASHER_TAPBRANCH} << node.sub[1]->hash << node.sub[1]->hash).GetSHA256() == node.hash) {
ComputeTapbranchHash(node.sub[1]->hash, node.sub[1]->hash) == node.hash) {
// Whenever there are nodes with two identical subtrees under it, we run into a problem:
// the control blocks for the leaves underneath those will be identical as well, and thus
// they will all be matched to the same path in the tree. The result is that at the location

7
src/test/script_tests.cpp
View File

@ -1817,7 +1817,14 @@ BOOST_AUTO_TEST_CASE(bip341_keypath_test_vectors)
}
}
}
BOOST_AUTO_TEST_CASE(compute_tapbranch)
{
uint256 hash1 = uint256S("8ad69ec7cf41c2a4001fd1f738bf1e505ce2277acdcaa63fe4765192497f47a7");
uint256 hash2 = uint256S("f224a923cd0021ab202ab139cc56802ddb92dcfc172b9212261a539df79a112a");
uint256 result = uint256S("a64c5b7b943315f9b805d7a7296bedfcfd08919270a1f7a1466e98f8693d8cd9");
BOOST_CHECK_EQUAL(ComputeTapbranchHash(hash1, hash2), result);
}
BOOST_AUTO_TEST_SUITE_END()