[2/2]: BIP 322 Support

btcutil/psbt/bip322.go

@@ -0,0 +1,187 @@
+package psbt
+
+import (
+	"encoding/base64"
+	"errors"
+
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
+)
+
+// BuildToSpendTx constructs a transaction to spend an output using the 
+// specified message and output script. It computes the message hash, 
+// constructs the scriptSig, and creates the to_spend transaction according to
+// BIP-322. For more details on BIP-322, see:
+// https://github.com/bitcoin/bips/blob/master/bip-0322.mediawiki
+//
+// Parameters:
+//   - message: The message to include in the transaction.
+//   - outPkScript: The output script to spend.
+//
+// Returns:
+//   - *wire.MsgTx: The constructed transaction.
+//   - error: An error if occurred during the construction.
+func BuildToSpendTx(message string, outPkScript []byte) (*wire.MsgTx, error) {
+	// Compute the message tagged hash:
+	// SHA256(SHA256(tag) || SHA256(tag) || message).
+	messageHash := *chainhash.TaggedHash(
+		chainhash.TagBIP0322SignedMsg, []byte(message),
+	)
+
+	// Construct the scriptSig - OP_0 PUSH32[ message_hash ].
+	scriptSigPartOne := []byte{0x00, 0x20}
+
+	// Convert messageHash to a byte slice.
+	messageHashBytes := messageHash[:]
+
+	// Create scriptSig with the length of scriptSigPartOne + messageHash.
+	scriptSig := make([]byte, len(scriptSigPartOne)+len(messageHashBytes))
+
+	// Copy scriptSigPartOne into scriptSig.
+	copy(scriptSig, scriptSigPartOne)
+
+	// Copy messageHash into scriptSig starting from
+	// the end of scriptSigPartOne.
+	copy(scriptSig[len(scriptSigPartOne):], messageHashBytes)
+
+	// Create to_spend transaction in accordance to BIP-322:
+	// https://github.com/bitcoin/bips/blob/master/bip-0322.mediawiki#full
+	toSpendTx := &wire.MsgTx{
+		Version:  0,
+		LockTime: 0,
+		TxIn: []*wire.TxIn{{
+			PreviousOutPoint: wire.OutPoint{
+				Index: 0xFFFFFFFF,
+			},
+			Sequence: 0,
+		}},
+		TxOut: []*wire.TxOut{{
+			Value:    0,
+			PkScript: outPkScript,
+		}},
+	}
+
+	pInputs := []PInput{{
+		FinalScriptSig: scriptSig,
+		WitnessScript:  []byte{},
+	}}
+
+	pOutputs := []POutput{{}}
+
+	psbt := &Packet{
+		UnsignedTx: toSpendTx,
+		Inputs: pInputs,
+		Outputs: pOutputs,
+	}
+
+	tx, err := Extract(psbt)
+	if err != nil {
+		return nil, err
+	}
+
+	return tx, nil
+}
+
+// BuildToSignTx constructs a transaction to prepare for signing using the
+// specified transaction ID, witness script, and additional parameters. It
+// creates the to_sign transaction according to BIP-322. For more details on
+// BIP-322, see: https://github.com/bitcoin/bips/blob/master/bip-0322.mediawiki
+//
+// Parameters:
+//   - toSpendTxId: The transaction ID of the output to spend.
+//   - witnessScript: The witness script corresponding to the output being
+//	spent.
+//   - isRedeemScript: Whether the witness script should be used as the redeem
+//	script.
+//   - tapInternalKey: The internal key for Taproot if applicable, or nil if 
+//	not used.
+//
+// Returns:
+//   - *Packet: The constructed Partially Signed Bitcoin Transaction (PSBT).
+//   - error: An error if occurred during the construction.
+func BuildToSignTx(toSpendTxId string, witnessScript []byte,
+	isRedeemScript bool, tapInternalKey []byte) (*Packet, error) {
+
+	toSpendTxIdHash, err := chainhash.NewHashFromStr(toSpendTxId)
+	if err != nil {
+		return nil, err
+	}
+
+	// Create to_sign transaction in accordance to BIP-322:
+	// https://github.com/bitcoin/bips/blob/master/bip-0322.mediawiki#full
+	toSignTx := &wire.MsgTx{
+		Version:  0,
+		LockTime: 0,
+		TxIn: []*wire.TxIn{{
+			PreviousOutPoint: wire.OutPoint{
+				Hash:  *toSpendTxIdHash,
+				Index: 0,
+			},
+			Sequence: 0,
+		}},
+		TxOut: []*wire.TxOut{{
+			Value:    0,
+			PkScript: []byte{txscript.OP_RETURN},
+		}},
+	}
+
+	pInputs := []PInput{{
+		WitnessUtxo: &wire.TxOut{
+			Value:    0,
+			PkScript: witnessScript,
+		},
+	}}
+
+	pOutputs := []POutput{{}}
+
+	psbt := &Packet{
+		UnsignedTx: toSignTx,
+		Inputs: pInputs,
+		Outputs: pOutputs,
+	}
+
+	// Create an updater for the psbt. This also performs a sanity check.
+	updater, err := NewUpdater(psbt)
+	if err != nil {
+		return nil, err
+	}
+
+	// Set redeemScript as witnessScript if isRedeemScript.
+	if isRedeemScript {
+		err = updater.AddInRedeemScript(witnessScript, 0)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// Set tapInternalKey if provided.
+	if tapInternalKey != nil {
+		err = updater.AddInTaprootInternalKey(tapInternalKey, 0)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return psbt, nil
+}
+
+// EncodeWitness encodes witness stack in a signed BIP-322 PSBT into
+// its base-64 encoded format. For more details on
+// BIP-322, see: https://github.com/bitcoin/bips/blob/master/bip-0322.mediawiki
+//
+// Parameters:
+//   - signedPsbt: The signed Partially Signed Bitcoin Transaction (PSBT).
+//
+// Returns:
+//   - string: The base-64 encoded witness stack.
+//   - error: An error if the witness data is empty.
+func EncodeWitness(signedPsbt *Packet) (string, error) {
+	witness := signedPsbt.Inputs[0].FinalScriptWitness
+	if len(witness) > 0 {
+		return base64.StdEncoding.EncodeToString(witness), nil
+	} else {
+		return "", errors.New("witness data is empty")
+	}
+
+}