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consensus refactor: extract ComputeTapleafHash, ComputeTaprootMerkleRoot

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This commit is contained in:
Pieter Wuille 2021-06-05 15:29:04 -07:00
parent 0f47e01d7d
commit 29e5dd1a5b
2 changed files with 28 additions and 10 deletions
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32
src/script/interpreter.cpp
View file

@ -1847,16 +1847,14 @@ static bool ExecuteWitnessScript(const Span<const valtype>& stack_span, const CS
return true; return true;
} }
static bool VerifyTaprootCommitment(const std::vector<unsigned char>& control, const std::vector<unsigned char>& program, const CScript& script, uint256& tapleaf_hash) uint256 ComputeTapleafHash(uint8_t leaf_version, const CScript& script)
{
return (CHashWriter(HASHER_TAPLEAF) << leaf_version << script).GetSHA256();
}
uint256 ComputeTaprootMerkleRoot(Span<const unsigned char> control, const uint256& tapleaf_hash)
{ {
const int path_len = (control.size() - TAPROOT_CONTROL_BASE_SIZE) / TAPROOT_CONTROL_NODE_SIZE; const int path_len = (control.size() - TAPROOT_CONTROL_BASE_SIZE) / TAPROOT_CONTROL_NODE_SIZE;
//! The internal pubkey (x-only, so no Y coordinate parity).
const XOnlyPubKey p{uint256(std::vector<unsigned char>(control.begin() + 1, control.begin() + TAPROOT_CONTROL_BASE_SIZE))};
//! The output pubkey (taken from the scriptPubKey).
const XOnlyPubKey q{uint256(program)};
// Compute the tapleaf hash.
tapleaf_hash = (CHashWriter(HASHER_TAPLEAF) << uint8_t(control[0] & TAPROOT_LEAF_MASK) << script).GetSHA256();
// Compute the Merkle root from the leaf and the provided path.
uint256 k = tapleaf_hash; uint256 k = tapleaf_hash;
for (int i = 0; i < path_len; ++i) { for (int i = 0; i < path_len; ++i) {
CHashWriter ss_branch{HASHER_TAPBRANCH}; CHashWriter ss_branch{HASHER_TAPBRANCH};
@ -1868,8 +1866,21 @@ static bool VerifyTaprootCommitment(const std::vector<unsigned char>& control, c
} }
k = ss_branch.GetSHA256(); k = ss_branch.GetSHA256();
} }
return k;
}
static bool VerifyTaprootCommitment(const std::vector<unsigned char>& control, const std::vector<unsigned char>& program, const uint256& tapleaf_hash)
{
assert(control.size() >= TAPROOT_CONTROL_BASE_SIZE);
assert(program.size() >= uint256::size());
//! The internal pubkey (x-only, so no Y coordinate parity).
const XOnlyPubKey p{uint256(std::vector<unsigned char>(control.begin() + 1, control.begin() + TAPROOT_CONTROL_BASE_SIZE))};
//! The output pubkey (taken from the scriptPubKey).
const XOnlyPubKey q{uint256(program)};
// Compute the Merkle root from the leaf and the provided path.
const uint256 merkle_root = ComputeTaprootMerkleRoot(control, tapleaf_hash);
// Verify that the output pubkey matches the tweaked internal pubkey, after correcting for parity. // Verify that the output pubkey matches the tweaked internal pubkey, after correcting for parity.
return q.CheckTapTweak(p, k, control[0] & 1); return q.CheckTapTweak(p, merkle_root, control[0] & 1);
} }
static bool VerifyWitnessProgram(const CScriptWitness& witness, int witversion, const std::vector<unsigned char>& program, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* serror, bool is_p2sh) static bool VerifyWitnessProgram(const CScriptWitness& witness, int witversion, const std::vector<unsigned char>& program, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* serror, bool is_p2sh)
@ -1929,7 +1940,8 @@ static bool VerifyWitnessProgram(const CScriptWitness& witness, int witversion,
if (control.size() < TAPROOT_CONTROL_BASE_SIZE || control.size() > TAPROOT_CONTROL_MAX_SIZE || ((control.size() - TAPROOT_CONTROL_BASE_SIZE) % TAPROOT_CONTROL_NODE_SIZE) != 0) { if (control.size() < TAPROOT_CONTROL_BASE_SIZE || control.size() > TAPROOT_CONTROL_MAX_SIZE || ((control.size() - TAPROOT_CONTROL_BASE_SIZE) % TAPROOT_CONTROL_NODE_SIZE) != 0) {
return set_error(serror, SCRIPT_ERR_TAPROOT_WRONG_CONTROL_SIZE); return set_error(serror, SCRIPT_ERR_TAPROOT_WRONG_CONTROL_SIZE);
} }
if (!VerifyTaprootCommitment(control, program, exec_script, execdata.m_tapleaf_hash)) { execdata.m_tapleaf_hash = ComputeTapleafHash(control[0] & TAPROOT_LEAF_MASK, exec_script);
if (!VerifyTaprootCommitment(control, program, execdata.m_tapleaf_hash)) {
return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH);
} }
execdata.m_tapleaf_hash_init = true; execdata.m_tapleaf_hash_init = true;

6
src/script/interpreter.h
View file

@ -317,6 +317,12 @@ public:
} }
}; };
/** Compute the BIP341 tapleaf hash from leaf version & script. */
uint256 ComputeTapleafHash(uint8_t leaf_version, const CScript& script);
/** 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);
bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* error = nullptr); bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* error = nullptr);
bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptError* error = nullptr); bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptError* error = nullptr);
bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CScriptWitness* witness, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* serror = nullptr); bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CScriptWitness* witness, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* serror = nullptr);