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CAT in Tapscript (BIP-347) #29247

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511aca8
Re-enable OP_CAT in tapscript
arminsabouri May 18, 2024
14ea1bd
test: add unit tests for OP_CAT
arminsabouri May 18, 2024
fff6edc
test: add functional test for OP_CAT spends
arminsabouri Aug 24, 2024
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3 changes: 2 additions & 1 deletion src/policy/policy.h
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Original file line number Diff line number Diff line change
Expand Up @@ -130,7 +130,8 @@ static constexpr script_verify_flags STANDARD_SCRIPT_VERIFY_FLAGS{MANDATORY_SCRI
SCRIPT_VERIFY_CONST_SCRIPTCODE |
SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_TAPROOT_VERSION |
SCRIPT_VERIFY_DISCOURAGE_OP_SUCCESS |
SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_PUBKEYTYPE};
SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_PUBKEYTYPE |
SCRIPT_VERIFY_DISCOURAGE_OP_CAT};

/** For convenience, standard but not mandatory verify flags. */
static constexpr script_verify_flags STANDARD_NOT_MANDATORY_VERIFY_FLAGS{STANDARD_SCRIPT_VERIFY_FLAGS & ~MANDATORY_SCRIPT_VERIFY_FLAGS};
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41 changes: 36 additions & 5 deletions src/script/interpreter.cpp
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Expand Up @@ -452,10 +452,16 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
if (opcode > OP_16 && ++nOpCount > MAX_OPS_PER_SCRIPT) {
return set_error(serror, SCRIPT_ERR_OP_COUNT);
}

// When OP_SUCCESS disabled opcodes (CVE-2010-5137) are
// redefined in tapscript, remove them from the if below
// and put them here
if (opcode == OP_CAT) {
return set_error(serror, SCRIPT_ERR_DISABLED_OPCODE); // Disabled opcodes (CVE-2010-5137).
}
}

if (opcode == OP_CAT ||
opcode == OP_SUBSTR ||
if (opcode == OP_SUBSTR ||
opcode == OP_LEFT ||
opcode == OP_RIGHT ||
opcode == OP_INVERT ||
Expand Down Expand Up @@ -519,6 +525,19 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
case OP_NOP:
break;

case OP_CAT:
{
if (stack.size() < 2)
return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
valtype& vch1 = stacktop(-2);
valtype& vch2 = stacktop(-1);
if (vch1.size() + vch2.size() > MAX_SCRIPT_ELEMENT_SIZE)
return set_error(serror, SCRIPT_ERR_PUSH_SIZE);
vch1.insert(vch1.end(), vch2.begin(), vch2.end());
stack.pop_back();
}
break;

case OP_CHECKLOCKTIMEVERIFY:
{
if (!(flags & SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY)) {
Expand Down Expand Up @@ -1844,10 +1863,19 @@ static bool ExecuteWitnessScript(const std::span<const valtype>& stack_span, con
}
// New opcodes will be listed here. May use a different sigversion to modify existing opcodes.
if (IsOpSuccess(opcode)) {
if (flags & SCRIPT_VERIFY_DISCOURAGE_OP_SUCCESS) {
return set_error(serror, SCRIPT_ERR_DISCOURAGE_OP_SUCCESS);
if (opcode == OP_CAT) {
if (flags & SCRIPT_VERIFY_DISCOURAGE_OP_CAT) {
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@rot13maxi rot13maxi Sep 12, 2024

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SCRIPT_VERIFY_DISCOURAGE_OP_CAT is acting as a CAT-specific SCRIPT_VERIFY_DISCOURAGE_OP_SUCCESS that can be turned off while still not relaying transasctions with other OP_SUCCESS opcodes. Since this is the first time we're carving out an OP_SUCCESS and doing this, it would be great to have a test that exercises the combinations of SCRIPT_VERIFY_DISCOURAGE_OP_CAT and SCRIPT_VERIFY_OP_CAT

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@arminsabouri arminsabouri Sep 17, 2024

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Great suggestion! Added some additional unit tests to script_tests.json testing different combinations of scripts with and without (SCRIPT_VERIFY_DISCOURAGE_OP_CAT, SCRIPT_VERIFY_OP_CAT and SCRIPT_VERIFY_DISCOURAGE_OP_SUCCESS)

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@ajtowns ajtowns Oct 9, 2024

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Added to the inquisition PR in bitcoin-inquisition#68

return set_error(serror, SCRIPT_ERR_DISCOURAGE_OP_CAT);
} else if (!(flags & SCRIPT_VERIFY_OP_CAT)) {
return set_success(serror);
}
} else {
// OP_SUCCESS behaviour
if (flags & SCRIPT_VERIFY_DISCOURAGE_OP_SUCCESS) {
return set_error(serror, SCRIPT_ERR_DISCOURAGE_OP_SUCCESS);
}
return set_success(serror);
}
return set_success(serror);
}
}

Expand Down Expand Up @@ -2190,6 +2218,9 @@ const std::map<std::string, script_verify_flag_name>& ScriptFlagNamesToEnum()
FLAG_NAME(DISCOURAGE_UPGRADABLE_PUBKEYTYPE),
FLAG_NAME(DISCOURAGE_OP_SUCCESS),
FLAG_NAME(DISCOURAGE_UPGRADABLE_TAPROOT_VERSION),
FLAG_NAME(OP_CAT),
FLAG_NAME(DISCOURAGE_OP_CAT),

};
#undef FLAG_NAME
return g_names_to_enum;
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4 changes: 4 additions & 0 deletions src/script/interpreter.h
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Expand Up @@ -145,6 +145,10 @@ enum class script_verify_flag_name : uint8_t {
// Making unknown public key versions (in BIP 342 scripts) non-standard
SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_PUBKEYTYPE,

// Support OP_CAT in tapscript
SCRIPT_VERIFY_OP_CAT,
SCRIPT_VERIFY_DISCOURAGE_OP_CAT,

// Constants to point to the highest flag in use. Add new flags above this line.
//
SCRIPT_VERIFY_END_MARKER
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1 change: 1 addition & 0 deletions src/script/script_error.cpp
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Expand Up @@ -76,6 +76,7 @@ std::string ScriptErrorString(const ScriptError serror)
case SCRIPT_ERR_DISCOURAGE_UPGRADABLE_TAPROOT_VERSION:
return "Taproot version reserved for soft-fork upgrades";
case SCRIPT_ERR_DISCOURAGE_OP_SUCCESS:
case SCRIPT_ERR_DISCOURAGE_OP_CAT:
return "OP_SUCCESSx reserved for soft-fork upgrades";
case SCRIPT_ERR_DISCOURAGE_UPGRADABLE_PUBKEYTYPE:
return "Public key version reserved for soft-fork upgrades";
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3 changes: 3 additions & 0 deletions src/script/script_error.h
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Expand Up @@ -78,6 +78,9 @@ typedef enum ScriptError_t
SCRIPT_ERR_TAPSCRIPT_CHECKMULTISIG,
SCRIPT_ERR_TAPSCRIPT_MINIMALIF,

/* OP_CAT re-activation */
SCRIPT_ERR_DISCOURAGE_OP_CAT,

/* Constant scriptCode */
SCRIPT_ERR_OP_CODESEPARATOR,
SCRIPT_ERR_SIG_FINDANDDELETE,
Expand Down
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