backend/btc: refactor pkScript encoding/decoding

We use functions from the btcd library to convert addresses to
pubKeyScripts and vice versa.

While the address type has support for Taproot addresses, the pubkey
script functions in btcd don't handle them yet. See also:
btcsuite/btcd#1768

To speed up send-to-taproot support, refactor the pubkey script
encoding/decoding into separate unit-tested functions, to which we can
easily add taproot support in the next commit.

backend/coins/btc/transaction.go

@@ -20,7 +20,6 @@ import (
 	"strconv"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
-	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
 	"github.com/digitalbitbox/bitbox-wallet-app/backend/accounts"
@@ -29,6 +28,7 @@ import (
 	"github.com/digitalbitbox/bitbox-wallet-app/backend/coins/btc/blockchain"
 	"github.com/digitalbitbox/bitbox-wallet-app/backend/coins/btc/maketx"
 	"github.com/digitalbitbox/bitbox-wallet-app/backend/coins/btc/transactions"
+	"github.com/digitalbitbox/bitbox-wallet-app/backend/coins/btc/util"
 	"github.com/digitalbitbox/bitbox-wallet-app/backend/coins/coin"
 	"github.com/digitalbitbox/bitbox-wallet-app/util/errp"
 )
@@ -80,9 +80,9 @@ func (account *Account) newTx(args *accounts.TxProposalArgs) (
 	if err != nil {
 		return nil, nil, err
 	}
-	pkScript, err := txscript.PayToAddrScript(address)
+	pkScript, err := util.PkScriptFromAddress(address)
 	if err != nil {
-		return nil, nil, errp.WithStack(err)
+		return nil, nil, err
 	}
 	utxo := account.transactions.SpendableOutputs()
 	wireUTXO := make(map[wire.OutPoint]maketx.UTXO, len(utxo))

backend/coins/btc/util/util.go

@@ -19,7 +19,9 @@ import (
 	"strings"
 
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcutil"
 	"github.com/digitalbitbox/bitbox-wallet-app/util/errp"
 )
 
@@ -39,3 +41,13 @@ func ParseOutPoint(outPointBytes []byte) (*wire.OutPoint, error) {
 	}
 	return wire.NewOutPoint(txHash, uint32(index)), nil
 }
+
+// PkScriptFromAddress decodes an address into the pubKeyScript that can be used in a transaction
+// output.
+func PkScriptFromAddress(address btcutil.Address) ([]byte, error) {
+	pkScript, err := txscript.PayToAddrScript(address)
+	if err != nil {
+		return nil, errp.WithStack(err)
+	}
+	return pkScript, nil
+}

backend/coins/btc/util/util_test.go

@@ -0,0 +1,63 @@
+// Copyright 2021 Shift Crypto AG
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package util
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/btcsuite/btcutil"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPkScriptFromAddress(t *testing.T) {
+	hash := []byte("\x92\x95\x3b\x69\x91\x29\x70\x02\xfa\xa6\x2a\x1d\xd2\x43\x13\xff\x62\x1e\x10\xab")
+	net := &chaincfg.MainNetParams
+
+	var address btcutil.Address
+
+	address, err := btcutil.NewAddressPubKeyHash(hash, net)
+	require.NoError(t, err)
+	pkScript, err := PkScriptFromAddress(address)
+	require.NoError(t, err)
+	require.Equal(t,
+		[]byte("\x76\xa9\x14\x92\x95\x3b\x69\x91\x29\x70\x02\xfa\xa6\x2a\x1d\xd2\x43\x13\xff\x62\x1e\x10\xab\x88\xac"),
+		pkScript)
+
+	address, err = btcutil.NewAddressWitnessPubKeyHash(hash, net)
+	require.NoError(t, err)
+	pkScript, err = PkScriptFromAddress(address)
+	require.NoError(t, err)
+	require.Equal(t,
+		[]byte("\x00\x14\x92\x95\x3b\x69\x91\x29\x70\x02\xfa\xa6\x2a\x1d\xd2\x43\x13\xff\x62\x1e\x10\xab"),
+		pkScript)
+
+	address, err = btcutil.NewAddressScriptHashFromHash(hash, net)
+	require.NoError(t, err)
+	pkScript, err = PkScriptFromAddress(address)
+	require.NoError(t, err)
+	require.Equal(t,
+		[]byte("\xa9\x14\x92\x95\x3b\x69\x91\x29\x70\x02\xfa\xa6\x2a\x1d\xd2\x43\x13\xff\x62\x1e\x10\xab\x87"),
+		pkScript)
+
+	scriptHash := []byte("\x4a\xf2\xe4\x54\x9a\x5c\xbb\x73\x6e\x77\xce\xf5\x2f\xe3\x0b\x9d\xf8\x12\x1d\x73\x56\xab\x20\x05\x46\x3e\xcb\x08\x97\x23\x45\x8d")
+	address, err = btcutil.NewAddressWitnessScriptHash(scriptHash, net)
+	require.NoError(t, err)
+	pkScript, err = PkScriptFromAddress(address)
+	require.NoError(t, err)
+	require.Equal(t,
+		[]byte("\x00\x20\x4a\xf2\xe4\x54\x9a\x5c\xbb\x73\x6e\x77\xce\xf5\x2f\xe3\x0b\x9d\xf8\x12\x1d\x73\x56\xab\x20\x05\x46\x3e\xcb\x08\x97\x23\x45\x8d"),
+		pkScript)
+}

backend/devices/bitbox02/keystore.go

@@ -278,6 +278,21 @@ func (keystore *keystore) ExtendedPublicKey(
 	}
 }
 
+func btcDecodePkScript(pkScript []byte, net *chaincfg.Params) (messages.BTCOutputType, []byte, error) {
+	scriptClass, addresses, _, err := txscript.ExtractPkScriptAddrs(pkScript, net)
+	if err != nil {
+		return 0, nil, errp.WithStack(err)
+	}
+	if len(addresses) != 1 {
+		return 0, nil, errp.New("couldn't parse pkScript")
+	}
+	msgOutputType, ok := btcMsgOutputTypeMap[scriptClass]
+	if !ok {
+		return 0, nil, errp.Newf("unsupported output type: %d", scriptClass)
+	}
+	return msgOutputType, addresses[0].ScriptAddress(), nil
+}
+
 func (keystore *keystore) signBTCTransaction(btcProposedTx *btc.ProposedTransaction) error {
 	tx := btcProposedTx.TXProposal.Transaction
 
@@ -351,16 +366,9 @@ func (keystore *keystore) signBTCTransaction(btcProposedTx *btc.ProposedTransact
 	}
 	outputs := make([]*messages.BTCSignOutputRequest, len(tx.TxOut))
 	for index, txOut := range tx.TxOut {
-		scriptClass, addresses, _, err := txscript.ExtractPkScriptAddrs(txOut.PkScript, coin.Net())
+		msgOutputType, payload, err := btcDecodePkScript(txOut.PkScript, coin.Net())
 		if err != nil {
-			return errp.WithStack(err)
-		}
-		if len(addresses) != 1 {
-			return errp.New("couldn't parse pkScript")
-		}
-		msgOutputType, ok := btcMsgOutputTypeMap[scriptClass]
-		if !ok {
-			return errp.Newf("unsupported output type: %d", scriptClass)
+			return err
 		}
 		changeAddress := btcProposedTx.TXProposal.ChangeAddress
 		isChange := changeAddress != nil && bytes.Equal(
@@ -375,7 +383,7 @@ func (keystore *keystore) signBTCTransaction(btcProposedTx *btc.ProposedTransact
 			Ours:    isChange,
 			Type:    msgOutputType,
 			Value:   uint64(txOut.Value),
-			Hash:    addresses[0].ScriptAddress(),
+			Payload: payload,
 			Keypath: keypath,
 		}
 	}

backend/devices/bitbox02/keystore_test.go

@@ -0,0 +1,69 @@
+// Copyright 2021 Shift Crypto AG
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package bitbox02
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/btcsuite/btcutil"
+	"github.com/digitalbitbox/bitbox-wallet-app/backend/coins/btc/util"
+	"github.com/digitalbitbox/bitbox02-api-go/api/firmware/messages"
+	"github.com/stretchr/testify/require"
+)
+
+func TesBtcDecodePkScript(t *testing.T) {
+	hash := []byte("\x92\x95\x3b\x69\x91\x29\x70\x02\xfa\xa6\x2a\x1d\xd2\x43\x13\xff\x62\x1e\x10\xab")
+	net := &chaincfg.MainNetParams
+
+	var address btcutil.Address
+
+	address, err := btcutil.NewAddressPubKeyHash(hash, net)
+	require.NoError(t, err)
+	pkScript, err := util.PkScriptFromAddress(address)
+	require.NoError(t, err)
+	outputType, payload, err := btcDecodePkScript(pkScript, &chaincfg.MainNetParams)
+	require.NoError(t, err)
+	require.Equal(t, messages.BTCOutputType_P2PKH, outputType)
+	require.Equal(t, address.ScriptAddress(), payload)
+
+	address, err = btcutil.NewAddressWitnessPubKeyHash(hash, net)
+	require.NoError(t, err)
+	pkScript, err = util.PkScriptFromAddress(address)
+	require.NoError(t, err)
+	outputType, payload, err = btcDecodePkScript(pkScript, &chaincfg.MainNetParams)
+	require.NoError(t, err)
+	require.Equal(t, messages.BTCOutputType_P2WPKH, outputType)
+	require.Equal(t, address.ScriptAddress(), payload)
+
+	address, err = btcutil.NewAddressScriptHashFromHash(hash, net)
+	require.NoError(t, err)
+	pkScript, err = util.PkScriptFromAddress(address)
+	require.NoError(t, err)
+	outputType, payload, err = btcDecodePkScript(pkScript, &chaincfg.MainNetParams)
+	require.NoError(t, err)
+	require.Equal(t, messages.BTCOutputType_P2SH, outputType)
+	require.Equal(t, address.ScriptAddress(), payload)
+
+	scriptHash := []byte("\x4a\xf2\xe4\x54\x9a\x5c\xbb\x73\x6e\x77\xce\xf5\x2f\xe3\x0b\x9d\xf8\x12\x1d\x73\x56\xab\x20\x05\x46\x3e\xcb\x08\x97\x23\x45\x8d")
+	address, err = btcutil.NewAddressWitnessScriptHash(scriptHash, net)
+	require.NoError(t, err)
+	pkScript, err = util.PkScriptFromAddress(address)
+	require.NoError(t, err)
+	outputType, payload, err = btcDecodePkScript(pkScript, &chaincfg.MainNetParams)
+	require.NoError(t, err)
+	require.Equal(t, messages.BTCOutputType_P2WSH, outputType)
+	require.Equal(t, address.ScriptAddress(), payload)
+}