taproot – Enable P2TR script path output using python bitcoinutils library

adminMarch 21, 2024

I’m trying to use the P2TR output using one of the scripts used to generate the current address. Below is some Python code that attempts to construct a raw transaction to use UTXOs. The address you want to move the testnet coins to is tb1pnnr3jysdew9gma9ac9k3pzdy5xp69fka3jh9vkga5ak28yjak0ws3hw834.

from bitcoinlib import transactions
from bitcoinutils.setup import setup
from bitcoinutils.script import Script
from bitcoinutils.utils import *
from bitcoinutils.transactions import Transaction, TxInput, TxOutput, TxWitnessInput
from bitcoinutils.keys import *

utxos = ('txid': "4390635a95c7e3538dda7c4690f38fbfaa5d93eaf04e1f4f63fb811a884428e2", "vout": 0)

priv1 = PrivateKey(wif="secret for obvious reason 1")
priv2 = PrivateKey(wif="secret for obvious reason 2")
priv3 = PrivateKey(wif="secret for obvious reason 3")
priv4 = PrivateKey(wif="secret for obvious reason 4")

pub1 = priv1.get_public_key()
pub2 = priv2.get_public_key()
pub3 = priv3.get_public_key()
pub4 = priv4.get_public_key()

def main():
    setup("testnet")

    input_amounts = (79800)
    output_amounts = (79650)

    # taproot script 2 is a simple P2PK with key 2
    tr_script_p2pk2 = Script((pub2.to_x_only_hex(), "OP_CHECKSIG"))

    # taproot script 3 is a simple P2PK with key 3
    tr_script_p2pk3 = Script((pub3.to_x_only_hex(), "OP_CHECKSIG"))

    # taproot script 4 is a simple P2PK with key 4
    tr_script_p2pk4 = Script((pub4.to_x_only_hex(), "OP_CHECKSIG"))

    all_leafs = ((tr_script_p2pk2, tr_script_p2pk3), tr_script_p2pk4)
    input_address = pub1.get_taproot_address(all_leafs)

    input_1 = TxInput(txid=utxos(4)('txid'), txout_index=utxos(4)('vout'))

    output_address = P2pkhAddress(address="moHfMJHAP3LE2aYTp4Q6g5GxnnfTK9muAJ")
    output_1 = TxOutput(amount=output_amounts(0), script_pubkey=output_address.to_script_pub_key())

    tx1 = Transaction(inputs=(input_1), outputs=(output_1), has_segwit=True)
    sig1 = priv3.sign_taproot_input(tx=tx1, txin_index=0, utxo_scripts=(input_address.to_script_pub_key()),
                                    amounts=input_amounts, script_path=True, 
                                    tapleaf_script=tr_script_p2pk3, tweak=False)

    # tagged hashes of leafs
    leaf2 = tapleaf_tagged_hash(tr_script_p2pk2)
    leaf3 = tapleaf_tagged_hash(tr_script_p2pk3)
    leaf4 = tapleaf_tagged_hash(tr_script_p2pk4)

    # If using get_tag_hashed_merkle_root
    merkleroot1 = get_tag_hashed_merkle_root(scripts=all_leafs)

    # If manually constructing the tree
    branch_23 = tapbranch_tagged_hash(leaf2, leaf3)
    merkleroot2 = tapbranch_tagged_hash(branch_23, leaf4)
    assert(merkleroot1.hex() == merkleroot2.hex())

    control_block = ControlBlock(pubkey=pub1, script_to_spend=tr_script_p2pk3, scripts=leaf2+leaf4)
    tx1.witnesses.append(TxWitnessInput((sig1, tr_script_p2pk3.to_hex(), control_block.to_hex())))
    print("\nRaw signed transaction:\n" + tx1.serialize())

Among the three scripts used to generate addresses, we are trying to use UTXO using tr_script_p2pk3. The raw transaction obtained by running this code is:

02000000 => version
0001 => marker and flag
01 => input count
e22844881a81fb634f1f4ef0ea935daabf8ff390467cda8d53e3c7955a639043 => input txid
00000000 => input vout
00 => scriptSig
ffffffff => nSequence
01 => output count
2237010000000000 => output amount
1976a914553d745f650e2faba231590931c3561e3ab7cb7888ac => scriptPubKey
03 => witness stack count
4060f3d6d5e5782977b53d6f7025ff8c7f70e1cb6a1b1de96117aa499713fcd701fed99f27d0922e58a8a8d731af9f3f9b36d5389e694b23513dd0b0eea6264fa7 => schnorr signature
222030a1dfffabb677eb2d8aa45bc7e24cbc31d67731680fe5be4b524e3359445f37ac => tr_script_p2pk3
61 => control block length
c0 => default leaf version tapscript
cded16e0e749cb161694b20f5bd7737ebc22b40805a415941b3fcc26df30dbb1 => internal key (in this example, pub1)
dff122122208c96d11efdd99a987150f7c422eeb2f9076f40804382dbc95c7b78cbca50495d9c133a60cf93e502e84b421b5640258f549c2bdb6e538eae16e7d => Merkle path (in this case, leaf2 + leaf4)
00000000 => nLocktime

The transaction failed and I received the following message: I also tried the same code, but I have an address with two tabroot script paths and the transaction was successfully broadcasted. In this case, the Merkle path must be a hash of the tapleaf tag from another script that was not used to unlock the UTXO. I think the error is related to the control block part, but I can’t figure out exactly where my code is going wrong. Can someone point out the problem?

adminMarch 21, 2024