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-rw-r--r--src/script/interpreter.cpp4
-rw-r--r--src/script/interpreter.h4
-rw-r--r--src/script/standard.cpp99
-rw-r--r--src/script/standard.h78
4 files changed, 183 insertions, 2 deletions
diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index 5f04d486b1..3c3c3ac1a8 100644
--- a/src/script/interpreter.cpp
+++ b/src/script/interpreter.cpp
@@ -1484,8 +1484,8 @@ template PrecomputedTransactionData::PrecomputedTransactionData(const CTransacti
template PrecomputedTransactionData::PrecomputedTransactionData(const CMutableTransaction& txTo);
static const CHashWriter HASHER_TAPSIGHASH = TaggedHash("TapSighash");
-static const CHashWriter HASHER_TAPLEAF = TaggedHash("TapLeaf");
-static const CHashWriter HASHER_TAPBRANCH = TaggedHash("TapBranch");
+const CHashWriter HASHER_TAPLEAF = TaggedHash("TapLeaf");
+const CHashWriter HASHER_TAPBRANCH = TaggedHash("TapBranch");
static bool HandleMissingData(MissingDataBehavior mdb)
{
diff --git a/src/script/interpreter.h b/src/script/interpreter.h
index 212de17c7b..fa4ee83e04 100644
--- a/src/script/interpreter.h
+++ b/src/script/interpreter.h
@@ -6,6 +6,7 @@
#ifndef BITCOIN_SCRIPT_INTERPRETER_H
#define BITCOIN_SCRIPT_INTERPRETER_H
+#include <hash.h>
#include <script/script_error.h>
#include <span.h>
#include <primitives/transaction.h>
@@ -218,6 +219,9 @@ static constexpr size_t TAPROOT_CONTROL_NODE_SIZE = 32;
static constexpr size_t TAPROOT_CONTROL_MAX_NODE_COUNT = 128;
static constexpr size_t TAPROOT_CONTROL_MAX_SIZE = TAPROOT_CONTROL_BASE_SIZE + TAPROOT_CONTROL_NODE_SIZE * TAPROOT_CONTROL_MAX_NODE_COUNT;
+extern const CHashWriter HASHER_TAPLEAF; //!< Hasher with tag "TapLeaf" pre-fed to it.
+extern const CHashWriter HASHER_TAPBRANCH; //!< Hasher with tag "TapBranch" pre-fed to it.
+
template <class T>
uint256 SignatureHash(const CScript& scriptCode, const T& txTo, unsigned int nIn, int nHashType, const CAmount& amount, SigVersion sigversion, const PrecomputedTransactionData* cache = nullptr);
diff --git a/src/script/standard.cpp b/src/script/standard.cpp
index 0a233b550a..a4b11cc0a9 100644
--- a/src/script/standard.cpp
+++ b/src/script/standard.cpp
@@ -6,8 +6,11 @@
#include <script/standard.h>
#include <crypto/sha256.h>
+#include <hash.h>
#include <pubkey.h>
+#include <script/interpreter.h>
#include <script/script.h>
+#include <util/strencodings.h>
#include <string>
@@ -370,3 +373,99 @@ CScript GetScriptForMultisig(int nRequired, const std::vector<CPubKey>& keys)
bool IsValidDestination(const CTxDestination& dest) {
return dest.index() != 0;
}
+
+/*static*/ TaprootBuilder::NodeInfo TaprootBuilder::Combine(NodeInfo&& a, NodeInfo&& b)
+{
+ NodeInfo ret;
+ /* 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();
+ } else {
+ ret.hash = (CHashWriter(HASHER_TAPBRANCH) << b.hash << a.hash).GetSHA256();
+ }
+ return ret;
+}
+
+void TaprootBuilder::Insert(TaprootBuilder::NodeInfo&& node, int depth)
+{
+ assert(depth >= 0 && (size_t)depth <= TAPROOT_CONTROL_MAX_NODE_COUNT);
+ /* We cannot insert a leaf at a lower depth while a deeper branch is unfinished. Doing
+ * so would mean the Add() invocations do not correspond to a DFS traversal of a
+ * binary tree. */
+ if ((size_t)depth + 1 < m_branch.size()) {
+ m_valid = false;
+ return;
+ }
+ /* As long as an entry in the branch exists at the specified depth, combine it and propagate up.
+ * The 'node' variable is overwritten here with the newly combined node. */
+ while (m_valid && m_branch.size() > (size_t)depth && m_branch[depth].has_value()) {
+ node = Combine(std::move(node), std::move(*m_branch[depth]));
+ m_branch.pop_back();
+ if (depth == 0) m_valid = false; /* Can't propagate further up than the root */
+ --depth;
+ }
+ if (m_valid) {
+ /* Make sure the branch is big enough to place the new node. */
+ if (m_branch.size() <= (size_t)depth) m_branch.resize((size_t)depth + 1);
+ assert(!m_branch[depth].has_value());
+ m_branch[depth] = std::move(node);
+ }
+}
+
+/*static*/ bool TaprootBuilder::ValidDepths(const std::vector<int>& depths)
+{
+ std::vector<bool> branch;
+ for (int depth : depths) {
+ // This inner loop corresponds to effectively the same logic on branch
+ // as what Insert() performs on the m_branch variable. Instead of
+ // storing a NodeInfo object, just remember whether or not there is one
+ // at that depth.
+ if (depth < 0 || (size_t)depth > TAPROOT_CONTROL_MAX_NODE_COUNT) return false;
+ if ((size_t)depth + 1 < branch.size()) return false;
+ while (branch.size() > (size_t)depth && branch[depth]) {
+ branch.pop_back();
+ if (depth == 0) return false;
+ --depth;
+ }
+ if (branch.size() <= (size_t)depth) branch.resize((size_t)depth + 1);
+ assert(!branch[depth]);
+ branch[depth] = true;
+ }
+ // And this check corresponds to the IsComplete() check on m_branch.
+ return branch.size() == 0 || (branch.size() == 1 && branch[0]);
+}
+
+TaprootBuilder& TaprootBuilder::Add(int depth, const CScript& script, int leaf_version)
+{
+ assert((leaf_version & ~TAPROOT_LEAF_MASK) == 0);
+ if (!IsValid()) return *this;
+ /* Construct NodeInfo object with leaf hash. */
+ NodeInfo node;
+ node.hash = (CHashWriter{HASHER_TAPLEAF} << uint8_t(leaf_version) << script).GetSHA256();
+ /* Insert into the branch. */
+ Insert(std::move(node), depth);
+ return *this;
+}
+
+TaprootBuilder& TaprootBuilder::AddOmitted(int depth, const uint256& hash)
+{
+ if (!IsValid()) return *this;
+ /* Construct NodeInfo object with the hash directly, and insert it into the branch. */
+ NodeInfo node;
+ node.hash = hash;
+ Insert(std::move(node), depth);
+ return *this;
+}
+
+TaprootBuilder& TaprootBuilder::Finalize(const XOnlyPubKey& internal_key)
+{
+ /* Can only call this function when IsComplete() is true. */
+ assert(IsComplete());
+ 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;
+ return *this;
+}
+
+WitnessV1Taproot TaprootBuilder::GetOutput() { return WitnessV1Taproot{m_output_key}; }
diff --git a/src/script/standard.h b/src/script/standard.h
index a96b096fa7..d7ea5cef27 100644
--- a/src/script/standard.h
+++ b/src/script/standard.h
@@ -209,4 +209,82 @@ CScript GetScriptForRawPubKey(const CPubKey& pubkey);
/** Generate a multisig script. */
CScript GetScriptForMultisig(int nRequired, const std::vector<CPubKey>& keys);
+/** Utility class to construct Taproot outputs from internal key and script tree. */
+class TaprootBuilder
+{
+private:
+ /** Information associated with a node in the Merkle tree. */
+ struct NodeInfo
+ {
+ /** Merkle hash of this node. */
+ uint256 hash;
+ };
+ /** Whether the builder is in a valid state so far. */
+ bool m_valid = true;
+
+ /** The current state of the builder.
+ *
+ * For each level in the tree, one NodeInfo object may be present. m_branch[0]
+ * is information about the root; further values are for deeper subtrees being
+ * explored.
+ *
+ * For every right branch taken to reach the position we're currently
+ * working in, there will be a (non-nullopt) entry in m_branch corresponding
+ * to the left branch at that level.
+ *
+ * For example, imagine this tree: - N0 -
+ * / \
+ * N1 N2
+ * / \ / \
+ * A B C N3
+ * / \
+ * D E
+ *
+ * Initially, m_branch is empty. After processing leaf A, it would become
+ * {nullopt, nullopt, A}. When processing leaf B, an entry at level 2 already
+ * exists, and it would thus be combined with it to produce a level 1 one,
+ * resulting in {nullopt, N1}. Adding C and D takes us to {nullopt, N1, C}
+ * and {nullopt, N1, C, D} respectively. When E is processed, it is combined
+ * with D, and then C, and then N1, to produce the root, resulting in {N0}.
+ *
+ * This structure allows processing with just O(log n) overhead if the leaves
+ * are computed on the fly.
+ *
+ * As an invariant, there can never be nullopt entries at the end. There can
+ * also not be more than 128 entries (as that would mean more than 128 levels
+ * in the tree). The depth of newly added entries will always be at least
+ * equal to the current size of m_branch (otherwise it does not correspond
+ * to a depth-first traversal of a tree). m_branch is only empty if no entries
+ * have ever be processed. m_branch having length 1 corresponds to being done.
+ */
+ std::vector<std::optional<NodeInfo>> m_branch;
+
+ XOnlyPubKey m_internal_key; //!< The internal key, set when finalizing.
+ XOnlyPubKey m_output_key; //!< The output key, computed when finalizing. */
+
+ /** Combine information about a parent Merkle tree node from its child nodes. */
+ static NodeInfo Combine(NodeInfo&& a, NodeInfo&& b);
+ /** Insert information about a node at a certain depth, and propagate information up. */
+ void Insert(NodeInfo&& node, int depth);
+
+public:
+ /** Add a new script at a certain depth in the tree. Add() operations must be called
+ * in depth-first traversal order of binary tree. */
+ TaprootBuilder& Add(int depth, const CScript& script, int leaf_version);
+ /** Like Add(), but for a Merkle node with a given hash to the tree. */
+ TaprootBuilder& AddOmitted(int depth, const uint256& hash);
+ /** Finalize the construction. Can only be called when IsComplete() is true.
+ internal_key.IsFullyValid() must be true. */
+ TaprootBuilder& Finalize(const XOnlyPubKey& internal_key);
+
+ /** Return true if so far all input was valid. */
+ bool IsValid() const { return m_valid; }
+ /** Return whether there were either no leaves, or the leaves form a Huffman tree. */
+ bool IsComplete() const { return m_valid && (m_branch.size() == 0 || (m_branch.size() == 1 && m_branch[0].has_value())); }
+ /** Compute scriptPubKey (after Finalize()). */
+ WitnessV1Taproot GetOutput();
+ /** Check if a list of depths is legal (will lead to IsComplete()). */
+ static bool ValidDepths(const std::vector<int>& depths);
+};
+
#endif // BITCOIN_SCRIPT_STANDARD_H