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make CHECKOUTPUTSVERIFY take stack arg, but check prev. executed opcode #3

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make CHECKOUTPUTSVERIFY take stack arg, but check prev. executed opcode #3

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43 changes: 31 additions & 12 deletions src/script/interpreter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -292,6 +292,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
CScript::const_iterator pend = script.end();
CScript::const_iterator pbegincodehash = script.begin();
opcodetype opcode;
opcodetype prev_opcode = OP_INVALIDOPCODE;
valtype vchPushValue;
std::vector<bool> vfExec;
std::vector<valtype> altstack;
Expand Down Expand Up @@ -774,18 +775,34 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
{
// Don't verify before enabled...
if (flags & SCRIPT_VERIFY_OUTPUTS_HASH) {
CScript::const_iterator lookahead = pc;
opcodetype argument;
// Read ahead one opcode as a lookahead argument
if (!script.GetOp(lookahead, argument, vchPushValue))
return set_error(serror, SCRIPT_ERR_BAD_OPCODE);
// If lookahead argument was exactly 32 bytes, check OutputHash

if (stack.size() < 1)
return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);

// Previous executed operation must be a data push.
//
// NOTE:
//
// INVALID_STACK_OPERATION might not be appropriate error code
// in this case, but this is closest thing in existing error codes.
//
// Making opcode behavior depend on the previous executed opcode
// adds complexity to the script execution model, but the amount
// of complexity added by this opcode-lookbehind mode is small,
// and this is arguably better than making non-pushdata
// opcodes use data lookahead, because this erodes the consistency
// of the stack machine execution model. The argument here seems
// to boil down to complexity vs model consistency.
// Reducing consistency just externalizes the complexity outside:
// to the users of the script and to the tools that operate on it.
if (prev_opcode > OP_PUSHDATA4)
return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);

valtype& vchHash = stacktop(-1);

// If stack argument was exactly 32 bytes, check OutputHash
// This is so that we can later add different semantics for this opcode
if (vchPushValue.size() == 32) {
// Argument should be == 0x20 -- will fail later anyways
if (!CheckMinimalPush(vchPushValue, argument)) {
return set_error(serror, SCRIPT_ERR_MINIMALDATA);
}
if (vchHash.size() == 32) {
// If multiple inputs allowed, two inputs with the same OutputsHashVerify
// would pay only half intended amount!
if (!checker.CheckOnlyOneInput()) {
Expand All @@ -796,7 +813,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
return set_error(serror, SCRIPT_ERR_OUTPUTSHASHVERIFY);
}
}

popstack(stack);
}
}
break;
Expand Down Expand Up @@ -1155,6 +1172,8 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
if (stack.size() + altstack.size() > MAX_STACK_SIZE)
return set_error(serror, SCRIPT_ERR_STACK_SIZE);

prev_opcode = opcode;

++opcode_pos;
}
}
Expand Down
6 changes: 3 additions & 3 deletions test/functional/feature_outputshashverify.py
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Original file line number Diff line number Diff line change
Expand Up @@ -23,10 +23,10 @@
def random_bytes(n):
return bytes(random.getrandbits(8) for i in range(n))
def random_fake_script():
return CScript([OP_CHECKOUTPUTSHASHVERIFY, random_bytes(32)])
return CScript([random_bytes(32), OP_CHECKOUTPUTSHASHVERIFY, OP_TRUE])
def random_real_outputs_and_script(n):
outputs = [CTxOut((x+1)*100, CScript(bytes([OP_RETURN, 0x20]) + random_bytes(32))) for x in range(n)]
return outputs, CScript(bytes([OP_CHECKOUTPUTSHASHVERIFY, 0x20]) + hash256(b"".join(o.serialize() for o in outputs)))
return outputs, CScript([hash256(b"".join(o.serialize() for o in outputs)), OP_CHECKOUTPUTSHASHVERIFY, OP_TRUE])

def random_tapscript_tree(depth):

Expand All @@ -39,7 +39,7 @@ def random_tapscript_tree(depth):
for d in range(1, depth+2):
idxs =zip(range(0, len(outputs_tree[-d]),2), range(1, len(outputs_tree[-d]), 2))
for (idx, (a,b)) in enumerate([(outputs_tree[-d][i], outputs_tree[-d][j]) for (i,j) in idxs]):
s = CScript(bytes([OP_CHECKOUTPUTSHASHVERIFY, 0x20]) + hash256(b"".join(o.serialize() for o in [a,b])))
s = CScript([hash256(b"".join(o.serialize() for o in [a,b])), OP_CHECKOUTPUTSHASHVERIFY, OP_TRUE])
a = sum(o.nValue for o in [a,b])
taproot, tweak, controls = taproot_construct(pubkey1, [s])
t = CTxOut(a+1000, taproot)
Expand Down