<p>I solved this problem, you can use the following code, it is equivalent to js's &quot;addDummySigs&quot;.</p>
<pre><code>    for index, input := range packet.Inputs {
        for _, pk := range pks {
            pkbz, _ := hex.DecodeString(pk)
            var signed bool
            for _, x := range input.TaprootScriptSpendSig {
                if bytes.Equal(pkbz, x.XOnlyPubKey) {
                    signed = true
                    break
                }
            }
            if !signed {
                packet.Inputs[index].TaprootScriptSpendSig = append(packet.Inputs[index].TaprootScriptSpendSig, &amp;psbt.TaprootScriptSpendSig{
                    XOnlyPubKey: pkbz,
                    LeafHash:    tapscript.tapleafHash,
                    Signature:   make([]byte, 0),
                    SigHash:     txscript.SigHashDefault,
                })
            }
        }

        sigs := packet.Inputs[index].TaprootScriptSpendSig
        sort.Slice(sigs, func(i, j int) bool {
            return bytes.Compare(sigs[i].XOnlyPubKey, sigs[j].XOnlyPubKey) &gt; 0
        })
        packet.Inputs[index].TaprootScriptSpendSig = sigs
    }
</code></pre>

CC BY-SA 4.0
2024-11-25T02:45:16.263Z
2024-11-25T02:45:16.263Z
Gang Li
<p>I have a 2-of-3 multisig taproot script,create like bitcoinjs-lib:<a href="https://github.com/bitcoinjs/bitcoinjs-lib/blob/8d9775c20da03ab40ccbb1971251e71d117bcd8b/test/integration/taproot.spec.ts#L531-L593" rel="nofollow noreferrer">https://github.com/bitcoinjs/bitcoinjs-lib/blob/8d9775c20da03ab40ccbb1971251e71d117bcd8b/test/integration/taproot.spec.ts#L531-L593</a>:</p>
<pre><code>builder := txscript.NewScriptBuilder()
for i, pk := range leafPubkeys {
    if i == 0 {
        builder.AddData(pk)
        builder.AddOp(byte(txscript.OP_CHECKSIG))
    } else {
        builder.AddData(pk)
        builder.AddOp(byte(txscript.OP_CHECKSIGADD))
    }
}
builder.AddOp(byte(txscript.OP_1 - 1 + 2))
builder.AddOp(byte(txscript.OP_GREATERTHANOREQUAL))
</code></pre>
<p>then create a tx(send satoshi from the script),and two keys sign it.but got &quot;invalid schnorr signatures&quot; when sent to bitcoind.
my golang code:</p>
<pre><code>func TestGenTapscript(t *testing.T) {
    signpks := []string{
...
    }
    pks := []string{...}
    tapscript := NewMultisigTaprootScript(pks, 2, 3, &amp;chaincfg.TestNet3Params)

    // build tx
    const utxoHash = &quot;...&quot;
    const utxoVout = 0
    const utxoAmount = 1000000
    const sendAmount = utxoAmount - 1000

    var (
        inputs     []*wire.OutPoint
        nSequences []uint32
        outputs    []*wire.TxOut
    )
    { // output
        ...
        outputs = append(outputs, redeemTxOut)
    }
    { // input
        ...
    }

    // Build PSBT
    packet, err := psbt.New(inputs, outputs, 2, 0, nSequences)
    if err != nil {
        t.Fatal(err)
    }
    packet.Inputs[0].TaprootLeafScript = []*psbt.TaprootTapLeafScript{
        &amp;psbt.TaprootTapLeafScript{
            ControlBlock: tapscript.controlBlock,
            Script:       tapscript.leafScript,
            LeafVersion:  0xc0,
        },
    }

    // update
    updater, err := psbt.NewUpdater(packet)
    if err != nil {
        t.Fatal(err)
    }
    if err := updater.AddInWitnessUtxo(wire.NewTxOut(utxoAmount, tapscript.output), 0); err != nil {
        t.Fatal(err)
    }

    var serializedTx bytes.Buffer
    if err := packet.Serialize(&amp;serializedTx); err != nil {
        t.Fatal(err)
    }
    psbtHex := hex.EncodeToString(serializedTx.Bytes())
    t.Log(&quot;psbtHex before sign:&quot;, psbtHex)

    // signit
    cu := cuabs.New()
    signedPsbtHex, err := cu.PsbtSign(context.Background(), signpks[0], psbtHex)
    if err != nil {
        t.Fatal(err)
    }
    signedPsbtHex, err = cu.PsbtSign(context.Background(), signpks[2], signedPsbtHex)
    if err != nil {
        t.Fatal(err)
    }
    t.Log(&quot;psbtHex after sign:&quot;, signedPsbtHex)

    // addDummySigs like bitcoinjs-lib
    psbtBz, _ := hex.DecodeString(signedPsbtHex)
    packet, err = psbt.NewFromRawBytes(bytes.NewReader(psbtBz), false)
    if err != nil {
        t.Fatal(err)
    }

    for index, input := range packet.Inputs {
        for _, pk := range pks {
            pkbz, _ := hex.DecodeString(pk)
            var signed bool
            for _, x := range input.TaprootScriptSpendSig {
                if bytes.Equal(pkbz, x.XOnlyPubKey) {
                    signed = true
                    break
                }
            }
            if !signed {
                packet.Inputs[index].TaprootScriptSpendSig = append(packet.Inputs[index].TaprootScriptSpendSig, &amp;psbt.TaprootScriptSpendSig{
                    XOnlyPubKey: pkbz,
                    LeafHash:    tapscript.tapleafHash,
                    Signature:   nil,
                    SigHash:     0,
                })
            }
        }

        // sigs := packet.Inputs[index].TaprootScriptSpendSig

        // sort.Slice(sigs, func(i, j int) bool {
        //  return bytes.Compare(sigs[i].XOnlyPubKey, sigs[j].XOnlyPubKey) &lt; 0
        // })
        // packet.Inputs[index].TaprootScriptSpendSig = sigs
    }

    {
        var serializedTx bytes.Buffer
        if err := packet.Serialize(&amp;serializedTx); err != nil {
            t.Fatal(err)
        }
        t.Log(&quot;psbtHex before finalize&quot;, hex.EncodeToString(serializedTx.Bytes()))
    }

    if err = psbt.MaybeFinalizeAll(packet); err != nil {
        t.Fatal(err)
    }
    {
        var serializedTx bytes.Buffer
        if err := packet.Serialize(&amp;serializedTx); err != nil {
            t.Fatal(err)
        }
        t.Log(&quot;psbtHex after finalize&quot;, hex.EncodeToString(serializedTx.Bytes()))
        
    }
    //extract()
    //broadcast()
}
</code></pre>
<p>Use js code,it work. &quot;tapscript.tapleafHash&quot; in golang is equal &quot;leafHash&quot; in js,and &quot;pubkey&quot; is equal.
After comparison, it was found that the &quot;psbtHex before finalize&quot; and &quot;psbtHex after finalize&quot; were different.
my js code:</p>
<pre><code>const psbt = bitcoin.Psbt.fromHex(signedPsbtHex)
{
  const leafHash = tapleafHash({
    output: leafScript,
    version: LEAF_VERSION_TAPSCRIPT,
  })
  console.log(leafHash.toString('hex'))
  for (const input of psbt.data.inputs) {
    if (!input.tapScriptSig) continue
    const signedPubkeys = input.tapScriptSig.filter((ts) =&gt; ts.leafHash.equals(leafHash)).map((ts) =&gt; ts.pubkey)
    for (const pubkey of leafPubkeys) {
      if (signedPubkeys.some((sPub) =&gt; sPub.equals(pubkey))) continue
      input.tapScriptSig.push({
        // This can be reused for each dummy signature
        leafHash,
        // This is the pubkey that didn't sign
        pubkey,
        // This must be an empty Buffer.
        signature: Buffer.from([]),
      })
    }
  }
} // this code from bitcoinjs-lib

psbt.finalizeAllInputs()
const tx = psbt.extractTransaction()
broadcast(...)
</code></pre>

<multi-signature><taproot><bip174-psbt><btcd><go-lang>
How "addDummySigs" in golang when send satoshi from p2tr multisig script?
Gang Li
# How "addDummySigs" in golang when send satoshi from p2tr multisig script?

(Asked by: username_0 on 2024-11-18)

I have a 2-of-3 multisig taproot script,create like bitcoinjs-lib:<https://github.com/bitcoinjs/bitcoinjs-lib/blob/8d9775c20da03ab40ccbb1971251e71d117bcd8b/test/integration/taproot.spec.ts#L531-L593>:

```
builder := txscript.NewScriptBuilder()
for i, pk := range leafPubkeys {
    if i == 0 {
        builder.AddData(pk)
        builder.AddOp(byte(txscript.OP_CHECKSIG))
    } else {
        builder.AddData(pk)
        builder.AddOp(byte(txscript.OP_CHECKSIGADD))
    }
}
builder.AddOp(byte(txscript.OP_1 - 1 + 2))
builder.AddOp(byte(txscript.OP_GREATERTHANOREQUAL))

```

then create a tx(send satoshi from the script),and two keys sign it.but got "invalid schnorr signatures" when sent to bitcoind.
my golang code:

```
func TestGenTapscript(t *testing.T) {
    signpks := []string{
...
    }
    pks := []string{...}
    tapscript := NewMultisigTaprootScript(pks, 2, 3, &chaincfg.TestNet3Params)

    // build tx
    const utxoHash = "..."
    const utxoVout = 0
    const utxoAmount = 1000000
    const sendAmount = utxoAmount - 1000

    var (
        inputs     []*wire.OutPoint
        nSequences []uint32
        outputs    []*wire.TxOut
    )
    { // output
        ...
        outputs = append(outputs, redeemTxOut)
    }
    { // input
        ...
    }

    // Build PSBT
    packet, err := psbt.New(inputs, outputs, 2, 0, nSequences)
    if err != nil {
        t.Fatal(err)
    }
    packet.Inputs[0].TaprootLeafScript = []*psbt.TaprootTapLeafScript{
        &psbt.TaprootTapLeafScript{
            ControlBlock: tapscript.controlBlock,
            Script:       tapscript.leafScript,
            LeafVersion:  0xc0,
        },
    }

    // update
    updater, err := psbt.NewUpdater(packet)
    if err != nil {
        t.Fatal(err)
    }
    if err := updater.AddInWitnessUtxo(wire.NewTxOut(utxoAmount, tapscript.output), 0); err != nil {
        t.Fatal(err)
    }

    var serializedTx bytes.Buffer
    if err := packet.Serialize(&serializedTx); err != nil {
        t.Fatal(err)
    }
    psbtHex := hex.EncodeToString(serializedTx.Bytes())
    t.Log("psbtHex before sign:", psbtHex)

    // signit
    cu := cuabs.New()
    signedPsbtHex, err := cu.PsbtSign(context.Background(), signpks[0], psbtHex)
    if err != nil {
        t.Fatal(err)
    }
    signedPsbtHex, err = cu.PsbtSign(context.Background(), signpks[2], signedPsbtHex)
    if err != nil {
        t.Fatal(err)
    }
    t.Log("psbtHex after sign:", signedPsbtHex)

    // addDummySigs like bitcoinjs-lib
    psbtBz, _ := hex.DecodeString(signedPsbtHex)
    packet, err = psbt.NewFromRawBytes(bytes.NewReader(psbtBz), false)
    if err != nil {
        t.Fatal(err)
    }

    for index, input := range packet.Inputs {
        for _, pk := range pks {
            pkbz, _ := hex.DecodeString(pk)
            var signed bool
            for _, x := range input.TaprootScriptSpendSig {
                if bytes.Equal(pkbz, x.XOnlyPubKey) {
                    signed = true
                    break
                }
            }
            if !signed {
                packet.Inputs[index].TaprootScriptSpendSig = append(packet.Inputs[index].TaprootScriptSpendSig, &psbt.TaprootScriptSpendSig{
                    XOnlyPubKey: pkbz,
                    LeafHash:    tapscript.tapleafHash,
                    Signature:   nil,
                    SigHash:     0,
                })
            }
        }

        // sigs := packet.Inputs[index].TaprootScriptSpendSig

        // sort.Slice(sigs, func(i, j int) bool {
        //  return bytes.Compare(sigs[i].XOnlyPubKey, sigs[j].XOnlyPubKey) < 0
        // })
        // packet.Inputs[index].TaprootScriptSpendSig = sigs
    }

    {
        var serializedTx bytes.Buffer
        if err := packet.Serialize(&serializedTx); err != nil {
            t.Fatal(err)
        }
        t.Log("psbtHex before finalize", hex.EncodeToString(serializedTx.Bytes()))
    }

    if err = psbt.MaybeFinalizeAll(packet); err != nil {
        t.Fatal(err)
    }
    {
        var serializedTx bytes.Buffer
        if err := packet.Serialize(&serializedTx); err != nil {
            t.Fatal(err)
        }
        t.Log("psbtHex after finalize", hex.EncodeToString(serializedTx.Bytes()))
        
    }
    //extract()
    //broadcast()
}

```

Use js code,it work. "tapscript.tapleafHash" in golang is equal "leafHash" in js,and "pubkey" is equal.
After comparison, it was found that the "psbtHex before finalize" and "psbtHex after finalize" were different.
my js code:

```
const psbt = bitcoin.Psbt.fromHex(signedPsbtHex)
{
  const leafHash = tapleafHash({
    output: leafScript,
    version: LEAF_VERSION_TAPSCRIPT,
  })
  console.log(leafHash.toString('hex'))
  for (const input of psbt.data.inputs) {
    if (!input.tapScriptSig) continue
    const signedPubkeys = input.tapScriptSig.filter((ts) => ts.leafHash.equals(leafHash)).map((ts) => ts.pubkey)
    for (const pubkey of leafPubkeys) {
      if (signedPubkeys.some((sPub) => sPub.equals(pubkey))) continue
      input.tapScriptSig.push({
        // This can be reused for each dummy signature
        leafHash,
        // This is the pubkey that didn't sign
        pubkey,
        // This must be an empty Buffer.
        signature: Buffer.from([]),
      })
    }
  }
} // this code from bitcoinjs-lib

psbt.finalizeAllInputs()
const tx = psbt.extractTransaction()
broadcast(...)

```

**Tags:** multi-signature, taproot, bip174-psbt, btcd, go-lang


---

## 1 answers

### Answer by username_0 on 2024-11-25. Score: 0

I solved this problem, you can use the following code, it is equivalent to js's "addDummySigs".

```
    for index, input := range packet.Inputs {
        for _, pk := range pks {
            pkbz, _ := hex.DecodeString(pk)
            var signed bool
            for _, x := range input.TaprootScriptSpendSig {
                if bytes.Equal(pkbz, x.XOnlyPubKey) {
                    signed = true
                    break
                }
            }
            if !signed {
                packet.Inputs[index].TaprootScriptSpendSig = append(packet.Inputs[index].TaprootScriptSpendSig, &psbt.TaprootScriptSpendSig{
                    XOnlyPubKey: pkbz,
                    LeafHash:    tapscript.tapleafHash,
                    Signature:   make([]byte, 0),
                    SigHash:     txscript.SigHashDefault,
                })
            }
        }

        sigs := packet.Inputs[index].TaprootScriptSpendSig
        sort.Slice(sigs, func(i, j int) bool {
            return bytes.Compare(sigs[i].XOnlyPubKey, sigs[j].XOnlyPubKey) > 0
        })
        packet.Inputs[index].TaprootScriptSpendSig = sigs
    }

```


---

