input: pass input.Signature to multisig spend

Modifies SpendMultiSig to accept input.Signature, so that we can
ultimately assert the size of multisig witnesses.

chancloser.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"fmt"
 
-	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
 	"github.com/davecgh/go-spew/spew"
@@ -510,11 +509,15 @@ func (c *channelCloser) ProcessCloseMsg(msg lnwire.Message) ([]lnwire.Message, b
 		// transaction!  We'll craft the final closing transaction so
 		// we can broadcast it to the network.
 		matchingSig := c.priorFeeOffers[remoteProposedFee].Signature
-		localSigBytes := matchingSig.ToSignatureBytes()
-		localSig := append(localSigBytes, byte(txscript.SigHashAll))
+		localSig, err := matchingSig.ToSignature()
+		if err != nil {
+			return nil, false, err
+		}
 
-		remoteSigBytes := closeSignedMsg.Signature.ToSignatureBytes()
-		remoteSig := append(remoteSigBytes, byte(txscript.SigHashAll))
+		remoteSig, err := closeSignedMsg.Signature.ToSignature()
+		if err != nil {
+			return nil, false, err
+		}
 
 		closeTx, _, err := c.cfg.channel.CompleteCooperativeClose(
 			localSig, remoteSig, c.localDeliveryScript,

input/script_utils.go

@@ -96,7 +96,9 @@ func GenFundingPkScript(aPub, bPub []byte, amt int64) ([]byte, *wire.TxOut, erro
 
 // SpendMultiSig generates the witness stack required to redeem the 2-of-2 p2wsh
 // multi-sig output.
-func SpendMultiSig(witnessScript, pubA, sigA, pubB, sigB []byte) [][]byte {
+func SpendMultiSig(witnessScript, pubA []byte, sigA Signature,
+	pubB []byte, sigB Signature) [][]byte {
+
 	witness := make([][]byte, 4)
 
 	// When spending a p2wsh multi-sig script, rather than an OP_0, we add
@@ -108,11 +110,11 @@ func SpendMultiSig(witnessScript, pubA, sigA, pubB, sigB []byte) [][]byte {
 	// ensure the signatures appear on the Script Virtual Machine stack in
 	// the correct order.
 	if bytes.Compare(pubA, pubB) == 1 {
-		witness[1] = sigB
-		witness[2] = sigA
+		witness[1] = append(sigB.Serialize(), byte(txscript.SigHashAll))
+		witness[2] = append(sigA.Serialize(), byte(txscript.SigHashAll))
 	} else {
-		witness[1] = sigA
-		witness[2] = sigB
+		witness[1] = append(sigA.Serialize(), byte(txscript.SigHashAll))
+		witness[2] = append(sigB.Serialize(), byte(txscript.SigHashAll))
 	}
 
 	// Finally, add the preimage as the last witness element.

lnwallet/channel.go

@@ -5065,18 +5065,22 @@ func (lc *LightningChannel) getSignedCommitTx() (*wire.MsgTx, error) {
 	// for the transaction.
 	localCommit := lc.channelState.LocalCommitment
 	commitTx := localCommit.CommitTx.Copy()
-	theirSig := append(localCommit.CommitSig, byte(txscript.SigHashAll))
+
+	theirSig, err := btcec.ParseDERSignature(
+		localCommit.CommitSig, btcec.S256(),
+	)
+	if err != nil {
+		return nil, err
+	}
 
 	// With this, we then generate the full witness so the caller can
 	// broadcast a fully signed transaction.
 	lc.signDesc.SigHashes = txscript.NewTxSigHashes(commitTx)
-	ourSigRaw, err := lc.Signer.SignOutputRaw(commitTx, lc.signDesc)
+	ourSig, err := lc.Signer.SignOutputRaw(commitTx, lc.signDesc)
 	if err != nil {
 		return nil, err
 	}
 
-	ourSig := append(ourSigRaw.Serialize(), byte(txscript.SigHashAll))
-
 	// With the final signature generated, create the witness stack
 	// required to spend from the multi-sig output.
 	ourKey := lc.channelState.LocalChanCfg.MultiSigKey.PubKey.
@@ -6017,7 +6021,8 @@ func (lc *LightningChannel) CreateCloseProposal(proposedFee btcutil.Amount,
 //
 // NOTE: The passed local and remote sigs are expected to be fully complete
 // signatures including the proper sighash byte.
-func (lc *LightningChannel) CompleteCooperativeClose(localSig, remoteSig []byte,
+func (lc *LightningChannel) CompleteCooperativeClose(
+	localSig, remoteSig input.Signature,
 	localDeliveryScript, remoteDeliveryScript []byte,
 	proposedFee btcutil.Amount) (*wire.MsgTx, btcutil.Amount, error) {
 
@@ -6070,8 +6075,10 @@ func (lc *LightningChannel) CompleteCooperativeClose(localSig, remoteSig []byte,
 		SerializeCompressed()
 	theirKey := lc.channelState.RemoteChanCfg.MultiSigKey.PubKey.
 		SerializeCompressed()
-	witness := input.SpendMultiSig(lc.signDesc.WitnessScript, ourKey,
-		localSig, theirKey, remoteSig)
+	witness := input.SpendMultiSig(
+		lc.signDesc.WitnessScript, ourKey, localSig, theirKey,
+		remoteSig,
+	)
 	closeTx.TxIn[0].Witness = witness
 
 	// Validate the finalized transaction to ensure the output script is

lnwallet/channel_test.go

@@ -616,7 +616,6 @@ func TestCooperativeChannelClosure(t *testing.T) {
 	if err != nil {
 		t.Fatalf("unable to create alice coop close proposal: %v", err)
 	}
-	aliceCloseSig := append(aliceSig.Serialize(), byte(txscript.SigHashAll))
 
 	bobFee := bobChannel.CalcFee(bobFeeRate)
 	bobSig, _, _, err := bobChannel.CreateCloseProposal(
@@ -625,14 +624,13 @@ func TestCooperativeChannelClosure(t *testing.T) {
 	if err != nil {
 		t.Fatalf("unable to create bob coop close proposal: %v", err)
 	}
-	bobCloseSig := append(bobSig.Serialize(), byte(txscript.SigHashAll))
 
 	// With the proposals created, both sides should be able to properly
 	// process the other party's signature. This indicates that the
 	// transaction is well formed, and the signatures verify.
 	aliceCloseTx, _, err := bobChannel.CompleteCooperativeClose(
-		bobCloseSig, aliceCloseSig, bobDeliveryScript,
-		aliceDeliveryScript, bobFee,
+		bobSig, aliceSig, bobDeliveryScript, aliceDeliveryScript,
+		bobFee,
 	)
 	if err != nil {
 		t.Fatalf("unable to complete alice cooperative close: %v", err)
@@ -640,8 +638,8 @@ func TestCooperativeChannelClosure(t *testing.T) {
 	bobCloseSha := aliceCloseTx.TxHash()
 
 	bobCloseTx, _, err := aliceChannel.CompleteCooperativeClose(
-		aliceCloseSig, bobCloseSig, aliceDeliveryScript,
-		bobDeliveryScript, aliceFee,
+		aliceSig, bobSig, aliceDeliveryScript, bobDeliveryScript,
+		aliceFee,
 	)
 	if err != nil {
 		t.Fatalf("unable to complete bob cooperative close: %v", err)
@@ -2054,24 +2052,25 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 	// balances. As a result, performing a cooperative closure now result
 	// in both sides having an output within the closure transaction.
 	aliceFee := btcutil.Amount(aliceChannel.CalcFee(aliceFeeRate)) + 1000
-	aliceSig, _, _, err := aliceChannel.CreateCloseProposal(aliceFee,
-		aliceDeliveryScript, bobDeliveryScript)
+	aliceSig, _, _, err := aliceChannel.CreateCloseProposal(
+		aliceFee, aliceDeliveryScript, bobDeliveryScript,
+	)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
-	aliceCloseSig := append(aliceSig.Serialize(), byte(txscript.SigHashAll))
 
 	bobFee := btcutil.Amount(bobChannel.CalcFee(bobFeeRate)) + 1000
-	bobSig, _, _, err := bobChannel.CreateCloseProposal(bobFee,
-		bobDeliveryScript, aliceDeliveryScript)
+	bobSig, _, _, err := bobChannel.CreateCloseProposal(
+		bobFee, bobDeliveryScript, aliceDeliveryScript,
+	)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
-	bobCloseSig := append(bobSig.Serialize(), byte(txscript.SigHashAll))
 
 	closeTx, _, err := bobChannel.CompleteCooperativeClose(
-		bobCloseSig, aliceCloseSig,
-		bobDeliveryScript, aliceDeliveryScript, bobFee)
+		bobSig, aliceSig, bobDeliveryScript, aliceDeliveryScript,
+		bobFee,
+	)
 	if err != nil {
 		t.Fatalf("unable to accept channel close: %v", err)
 	}
@@ -2093,23 +2092,24 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 
 	// Attempt another cooperative channel closure. It should succeed
 	// without any issues.
-	aliceSig, _, _, err = aliceChannel.CreateCloseProposal(aliceFee,
-		aliceDeliveryScript, bobDeliveryScript)
+	aliceSig, _, _, err = aliceChannel.CreateCloseProposal(
+		aliceFee, aliceDeliveryScript, bobDeliveryScript,
+	)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
-	aliceCloseSig = append(aliceSig.Serialize(), byte(txscript.SigHashAll))
 
-	bobSig, _, _, err = bobChannel.CreateCloseProposal(bobFee,
-		bobDeliveryScript, aliceDeliveryScript)
+	bobSig, _, _, err = bobChannel.CreateCloseProposal(
+		bobFee, bobDeliveryScript, aliceDeliveryScript,
+	)
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
-	bobCloseSig = append(bobSig.Serialize(), byte(txscript.SigHashAll))
 
 	closeTx, _, err = bobChannel.CompleteCooperativeClose(
-		bobCloseSig, aliceCloseSig,
-		bobDeliveryScript, aliceDeliveryScript, bobFee)
+		bobSig, aliceSig, bobDeliveryScript, aliceDeliveryScript,
+		bobFee,
+	)
 	if err != nil {
 		t.Fatalf("unable to accept channel close: %v", err)
 	}
@@ -2141,7 +2141,6 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
-	aliceCloseSig = append(aliceSig.Serialize(), byte(txscript.SigHashAll))
 
 	bobSig, _, _, err = bobChannel.CreateCloseProposal(
 		bobFee, bobDeliveryScript, aliceDeliveryScript,
@@ -2149,11 +2148,11 @@ func TestCooperativeCloseDustAdherence(t *testing.T) {
 	if err != nil {
 		t.Fatalf("unable to close channel: %v", err)
 	}
-	bobCloseSig = append(bobSig.Serialize(), byte(txscript.SigHashAll))
 
 	closeTx, _, err = bobChannel.CompleteCooperativeClose(
-		bobCloseSig, aliceCloseSig,
-		bobDeliveryScript, aliceDeliveryScript, bobFee)
+		bobSig, aliceSig, bobDeliveryScript, aliceDeliveryScript,
+		bobFee,
+	)
 	if err != nil {
 		t.Fatalf("unable to accept channel close: %v", err)
 	}

lnwallet/chanvalidate/validate_test.go

@@ -98,7 +98,7 @@ func newChannelTestCtx(chanSize int64) (*channelTestCtx, error) {
 	}
 
 	sigHashes := txscript.NewTxSigHashes(commitTx)
-	aliceSig, err := txscript.RawTxInWitnessSignature(
+	aliceSigRaw, err := txscript.RawTxInWitnessSignature(
 		commitTx, sigHashes, 0, chanSize,
 		multiSigScript, txscript.SigHashAll, alicePriv,
 	)
@@ -106,7 +106,14 @@ func newChannelTestCtx(chanSize int64) (*channelTestCtx, error) {
 		return nil, err
 	}
 
-	bobSig, err := txscript.RawTxInWitnessSignature(
+	aliceSig, err := btcec.ParseDERSignature(
+		aliceSigRaw, btcec.S256(),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	bobSigRaw, err := txscript.RawTxInWitnessSignature(
 		commitTx, sigHashes, 0, chanSize,
 		multiSigScript, txscript.SigHashAll, bobPriv,
 	)
@@ -114,6 +121,13 @@ func newChannelTestCtx(chanSize int64) (*channelTestCtx, error) {
 		return nil, err
 	}
 
+	bobSig, err := btcec.ParseDERSignature(
+		bobSigRaw, btcec.S256(),
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	commitTx.TxIn[0].Witness = input.SpendMultiSig(
 		multiSigScript, alicePub.SerializeCompressed(), aliceSig,
 		bobPub.SerializeCompressed(), bobSig,

lnwallet/test_utils.go

@@ -1,7 +1,6 @@
 package lnwallet
 
 import (
-	"bytes"
 	"crypto/rand"
 	"encoding/binary"
 	"encoding/hex"
@@ -81,6 +80,19 @@ var (
 		},
 		LockTime: 5,
 	}
+
+	// A valid, DER-encoded signature (taken from btcec unit tests).
+	testSigBytes = []byte{
+		0x30, 0x44, 0x02, 0x20, 0x4e, 0x45, 0xe1, 0x69,
+		0x32, 0xb8, 0xaf, 0x51, 0x49, 0x61, 0xa1, 0xd3,
+		0xa1, 0xa2, 0x5f, 0xdf, 0x3f, 0x4f, 0x77, 0x32,
+		0xe9, 0xd6, 0x24, 0xc6, 0xc6, 0x15, 0x48, 0xab,
+		0x5f, 0xb8, 0xcd, 0x41, 0x02, 0x20, 0x18, 0x15,
+		0x22, 0xec, 0x8e, 0xca, 0x07, 0xde, 0x48, 0x60,
+		0xa4, 0xac, 0xdd, 0x12, 0x90, 0x9d, 0x83, 0x1c,
+		0xc5, 0x6c, 0xbb, 0xac, 0x46, 0x22, 0x08, 0x22,
+		0x21, 0xa8, 0x76, 0x8d, 0x1d, 0x09,
+	}
 )
 
 // CreateTestChannels creates to fully populated channels to be used within
@@ -257,7 +269,7 @@ func CreateTestChannels(chanType channeldb.ChannelType) (
 		CommitFee:     commitFee,
 		FeePerKw:      btcutil.Amount(feePerKw),
 		CommitTx:      aliceCommitTx,
-		CommitSig:     bytes.Repeat([]byte{1}, 71),
+		CommitSig:     testSigBytes,
 	}
 	bobCommit := channeldb.ChannelCommitment{
 		CommitHeight:  0,
@@ -266,7 +278,7 @@ func CreateTestChannels(chanType channeldb.ChannelType) (
 		CommitFee:     commitFee,
 		FeePerKw:      btcutil.Amount(feePerKw),
 		CommitTx:      bobCommitTx,
-		CommitSig:     bytes.Repeat([]byte{1}, 71),
+		CommitSig:     testSigBytes,
 	}
 
 	var chanIDBytes [8]byte