Implement SCRIPT_VERIFY_NULLDUMMY

Author: petertodd

bitcoin/core/scripteval.py

@@ -152,7 +152,7 @@ def _CheckSig(sig, pubkey, script, txTo, inIdx, err_raiser):
     return key.verify(h, sig)
 
 
-def _CheckMultiSig(opcode, script, stack, txTo, inIdx, err_raiser, nOpCount):
+def _CheckMultiSig(opcode, script, stack, txTo, inIdx, flags, err_raiser, nOpCount):
     i = 1
     if len(stack) < i:
         err_raiser(MissingOpArgumentsError, opcode, stack, i)
@@ -209,10 +209,18 @@ def _CheckMultiSig(opcode, script, stack, txTo, inIdx, err_raiser, nOpCount):
             if opcode == OP_CHECKMULTISIGVERIFY:
                 err_raiser(VerifyOpFailedError, opcode)
 
-    while i > 0:
+    while i > 1:
         stack.pop()
         i -= 1
 
+    # Note how Bitcoin Core duplicates the len(stack) check, rather than
+    # letting pop() handle it; maybe that's wrong?
+    if len(stack) and SCRIPT_VERIFY_NULLDUMMY in flags:
+        if stack[-1] != b'':
+            raise err_raiser(ArgumentsInvalidError, opcode, "dummy value not OP_0")
+
+    stack.pop()
+
     if opcode == OP_CHECKMULTISIG:
         if success:
             stack.append(b"\x01")
@@ -478,7 +486,7 @@ def check_args(n):
 
             elif sop == OP_CHECKMULTISIG or sop == OP_CHECKMULTISIGVERIFY:
                 tmpScript = CScript(scriptIn[pbegincodehash:])
-                _CheckMultiSig(sop, tmpScript, stack, txTo, inIdx, err_raiser, nOpCount)
+                _CheckMultiSig(sop, tmpScript, stack, txTo, inIdx, flags, err_raiser, nOpCount)
 
             elif sop == OP_CHECKSIG or sop == OP_CHECKSIGVERIFY:
                 check_args(2)

bitcoin/tests/data/script_invalid.json

@@ -509,6 +509,18 @@
     "STRICTENC",
     "P2PK NOT with hybrid pubkey"
 ],
+[
+    "1 0x47 0x3044022051254b9fb476a52d85530792b578f86fea70ec1ffb4393e661bcccb23d8d63d3022076505f94a403c86097841944e044c70c2045ce90e36de51f7e9d3828db98a07501 0x47 0x304402200a358f750934b3feb822f1966bfcd8bbec9eeaa3a8ca941e11ee5960e181fa01022050bf6b5a8e7750f70354ae041cb68a7bade67ec6c3ab19eb359638974410626e01 0x47 0x304402200955d031fff71d8653221e85e36c3c85533d2312fc3045314b19650b7ae2f81002202a6bb8505e36201909d0921f01abff390ae6b7ff97bbf959f98aedeb0a56730901",
+    "3 0x21 0x0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798 0x21 0x038282263212c609d9ea2a6e3e172de238d8c39cabd5ac1ca10646e23fd5f51508 0x21 0x03363d90d447b00c9c99ceac05b6262ee053441c7e55552ffe526bad8f83ff4640 3 CHECKMULTISIG",
+    "NULLDUMMY",
+    "3-of-3 with nonzero dummy"
+],
+[
+    "1 0x47 0x304402201bb2edab700a5d020236df174fefed78087697143731f659bea59642c759c16d022061f42cdbae5bcd3e8790f20bf76687443436e94a634321c16a72aa54cbc7c2ea01 0x47 0x304402204bb4a64f2a6e5c7fb2f07fef85ee56fde5e6da234c6a984262307a20e99842d702206f8303aaba5e625d223897e2ffd3f88ef1bcffef55f38dc3768e5f2e94c923f901 0x47 0x3044022040c2809b71fffb155ec8b82fe7a27f666bd97f941207be4e14ade85a1249dd4d02204d56c85ec525dd18e29a0533d5ddf61b6b1bb32980c2f63edf951aebf7a27bfe01",
+    "3 0x21 0x0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798 0x21 0x038282263212c609d9ea2a6e3e172de238d8c39cabd5ac1ca10646e23fd5f51508 0x21 0x03363d90d447b00c9c99ceac05b6262ee053441c7e55552ffe526bad8f83ff4640 3 CHECKMULTISIG NOT",
+    "NULLDUMMY",
+    "3-of-3 NOT with invalid sig with nonzero dummy"
+],
 [
     "0x47 0x304402203e4516da7253cf068effec6b95c41221c0cf3a8e6ccb8cbf1725b562e9afde2c022054e1c258c2981cdfba5df1f46661fb6541c44f77ca0092f3600331abfffb125101 0x23 0x2103363d90d447b00c9c99ceac05b6262ee053441c7e55552ffe526bad8f83ff4640ac",
     "0x21 0x03363d90d447b00c9c99ceac05b6262ee053441c7e55552ffe526bad8f83ff4640 CHECKSIG",