Using the Bitcoin Crate to Sign a Segwit Transaction

Question

Using the Bitcoin crate, I'm trying to create a transaction programmatically in Rust that spends an output associated with a P2WPKH address. This is the relevant code snippet:

fn sign_transaction<SignFun>(
    own_public_key: &[u8],
    own_address: &Address,
    own_utxos: &[Utxo],
    mut transaction: Transaction,
    key_name: String,
    derivation_path: Vec<Vec<u8>>,
    signer: SignFun,
) -> Transaction
where
    SignFun: Fn(String, Vec<Vec<u8>>, Vec<u8>) -> Vec<u8>,
{

    let txclone = transaction.clone();
    let mut hash_cache = sighash::SighashCache::new(&txclone);
    for (index, input) in transaction.input.iter_mut().enumerate() {
        let value = get_value(input, own_utxos);    // Look up the value by finding the corresponding UTXO
        let sighash = hash_cache
            .segwit_signature_hash(index, &own_address.script_pubkey(), value, SIG_HASH_TYPE)
            .expect("Creating the segwit signature hash failed.");

        let signature = signer(key_name.clone(), derivation_path.clone(), sighash.to_vec()).await;

        // Convert signature to DER.
        let der_signature = sec1_to_der(signature);

        let mut sig_with_hashtype = der_signature;
        sig_with_hashtype.push(SIG_HASH_TYPE.to_u32() as u8);
        let witness_bytes = vec![sig_with_hashtype, own_public_key.to_vec()];
        input.witness = Witness::from_vec(witness_bytes);
    }

    transaction
}

When sending a signed transaction to my local Bitcoin node in RegTest mode, I get the following error:

error code: -26
error message:
non-mandatory-script-verify-flag (Signature must be zero for failed CHECK(MULTI)SIG operation)

I logged the following information:

• Public key: 0377f5de845ac601f24e7cbf2e4abcc9e1040cd4ae971ecaa00837b1c74684e15b
• Address: bcrt1qh3zle7xs34azdyycg8cpf9wx5nxjpcqyqv4eyc
• Input spent with value: 625000000
• Transaction to sign: 0100000001ceac446d9350730c2a886220bed7ae154ca3f717897819091d5e72dcd0f0895e00000 00000ffffffff0200e1f505000000001600148be949ae15ee4b5da9af0ce2bf8d3f3c43c582da26 dc4a1f00000000160014bc45fcf8d08d7a26909841f01495c6a4cd20e00400000000
• Sighash: d7e5696f18363b58c84b8d57014d291c9f7ebbac562d219f7e7014b9a5685bbf
• SEC1 signature: c10c09b210914e49f295c07c9f96352e085df9d2c4272292239445d6f89483bc64c9903bebaba4b bf998d217c80375c36b60b212a824b63435e30205b2ed5a6a
• DER signature: 3045022100c10c09b210914e49f295c07c9f96352e085df9d2c4272292239445d6f89483bc02206 4c9903bebaba4bbf998d217c80375c36b60b212a824b63435e30205b2ed5a6a
• DER signature with Sighash type: 3045022100c10c09b210914e49f295c07c9f96352e085df9d2c4272292239445d6f89483bc02206 4c9903bebaba4bbf998d217c80375c36b60b212a824b63435e30205b2ed5a6a01
• Signed transaction: 01000000000101ceac446d9350730c2a886220bed7ae154ca3f717897819091d5e72dcd0f0895e0 000000000ffffffff0200e1f505000000001600148be949ae15ee4b5da9af0ce2bf8d3f3c43c582 da26dc4a1f00000000160014bc45fcf8d08d7a26909841f01495c6a4cd20e00402483045022100c 10c09b210914e49f295c07c9f96352e085df9d2c4272292239445d6f89483bc022064c9903bebab a4bbf998d217c80375c36b60b212a824b63435e30205b2ed5a6a01210377f5de845ac601f24e7cb f2e4abcc9e1040cd4ae971ecaa00837b1c74684e15b00000000

Note that a similar piece of code for legacy (P2PKH) transactions using the same ECDSA signer works perfectly, so I'm assuming the signer is okay.

Any help to figure out where the problem lies would be greatly appreciated!

Answer 1

Even when the rawtransaction is right, if you give the wrong script_pubkey, it will generate wrong sighash. Just try to make sure that you are giving the right one. Try giving p2pkh script_pubkey of your pubkey.

let public_key = PublicKey::from_slice(own_public_key).unwrap();    
let script_code = bitcoin::Address::p2pkh(&public_key, bitcoin::network::constants::Network::Testnet).script_pubkey();
let sighash = hash_cache
        .segwit_signature_hash(index, &script_code, value, SIG_HASH_TYPE)
        .expect("Creating the segwit signature hash failed.");