Nonstandard witness when building a transaction

Question

i try to spend a P2WSH 2of2 multisig input in Python for learning purposes. When i check my assembled TX with testmempoolaccept i get "bad-witness-nonstandard".

This is my function to assemble the witness:

def get_p2wsh_witness(privs: List[bytes], msg: bytes) -> bytes:
    sigs = [sign(priv, msg) for priv in privs]
    witness = bytes.fromhex("04")
    witness += bytes.fromhex("00")
    for sig in sigs:
        witness += len(sig).to_bytes(1, "little") + sig
    musig_script = b""
    op2 = bytes.fromhex("52")
    op_checkmultisig = bytes.fromhex("ae")
    musig_script += op2
    for key in privs:
        key = get_pub_from_priv(key)
        musig_script += bytes.fromhex("21")  # 33 bytes
        musig_script += key
    musig_script += op2
    musig_script += op_checkmultisig
    musig_script = len(musig_script).to_bytes(1, "little") + musig_script
    witness += musig_script
    return witness

This is how i assembled the commitment hash:

def get_commitment_hash(outpoint: bytes, scriptcode: bytes, value: int, outputs: List[bytes]) -> bytes:
    def dsha256(data: bytes) -> bytes:
        return hashlib.new("sha256", hashlib.new("sha256", data).digest()).digest()
    result = b""
    result += (2).to_bytes(4, "little")
    result += dsha256(outpoint)  # hashPrevouts
    result += dsha256(bytes.fromhex("ffffffff"))
    result += outpoint
    # Passed scriptcode (hex): 522103abd618be2d6e412bb31457bf416cf05138592da9ab4c9647a79577492710eacb2103bc2e2480bd8f5a66d45ceb333db45a980283a3c55df3c23eed22f30aa99e82e852ae 
    if len(scriptcode) > 30:
        result += len(scriptcode).to_bytes(1, "little") + scriptcode
    else:
        result += scriptcode
    result += value.to_bytes(8, "little")
    result += bytes.fromhex("ffffffff")
    result += dsha256(b"".join(outputs))
    result += bytes.fromhex("00000000")
    result += bytes.fromhex("01000000")
    return dsha256(result)

This is the UTXO's origin transaction:

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
0400483045022100ec7dfded7d97f8d990d8470b0855a705c118dff718aed9f5a6c5faa24c33a03402207919d822f44bb3a36ffb0771e2e4dc99688e002e26a71fc53224eba84aa526d6014830450221009535cda9d3533a8b95ab3cbd8004b1fc4d689d5104ae0c027b4e857a6345e54b022020b8df4231a2fb0fbcbf2d7593f0fbdb63d72feea04167afcd1708fba130dd8a0147522103abd618be2d6e412bb31457bf416cf05138592da9ab4c9647a79577492710eacb2103bc2e2480bd8f5a66d45ceb333db45a980283a3c55df3c23eed22f30aa99e82e852ae

These are the (private signet) private keys in hex to sign with:

3e2d99b06d1e763e8a208d0f2522432596fc1ae75825e777fb6b04ecf7260848 27d7edd524be491da6f5996e830e92b5477844800155e47f672cd5527f3a0e7d

This is the final assembled tx, spending to one OP_Return and change:

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

Can anybody see an obvious mistake here, assuming sign() and the given keys are correct, or give a hint on how to verify the output myself?

Answer 1

The problem is you're creating a bare multisig output, not a P2WSH output. When you're subsequently trying to spend it as if it were a P2WSH output, Bitcoin Core errors because bare multisig inputs aren't supposed to have witness items.