lnwire: add new HtlcPoint to OpenChannel and AcceptChannel

In this commit, we begin implementing the latest spec change to reduce
the attack surface on online channels. In this commit, we introduce a
distinct HTLC base point which will be used to sign the second-level
HTLC transactions for each active HLTC on the commitment transaction of
the remote node. With this, we allow the commitment key to remain
offline, as it isn’t needed in routine channel updates, unless we need
to go to chain.

lnwire/accept_channel.go

@@ -75,6 +75,12 @@ type AcceptChannel struct {
 	// where they claim funds.
 	DelayedPaymentPoint *btcec.PublicKey
 
+	// HtlcPoint is the base point used to derive the set of keys for this
+	// party that will be used within the HTLC public key scripts.  This
+	// value is combined with the receiver's revocation base point in order
+	// to derive the keys that are used within HTLC scripts.
+	HtlcPoint *btcec.PublicKey
+
 	// FirstCommitmentPoint is the first commitment point for the sending
 	// party. This value should be combined with the receiver's revocation
 	// base point in order to derive the revocation keys that are placed
@@ -105,6 +111,7 @@ func (a *AcceptChannel) Encode(w io.Writer, pver uint32) error {
 		a.RevocationPoint,
 		a.PaymentPoint,
 		a.DelayedPaymentPoint,
+		a.HtlcPoint,
 		a.FirstCommitmentPoint,
 	)
 }
@@ -128,6 +135,7 @@ func (a *AcceptChannel) Decode(r io.Reader, pver uint32) error {
 		&a.RevocationPoint,
 		&a.PaymentPoint,
 		&a.DelayedPaymentPoint,
+		&a.HtlcPoint,
 		&a.FirstCommitmentPoint,
 	)
 }
@@ -145,6 +153,6 @@ func (a *AcceptChannel) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (a *AcceptChannel) MaxPayloadLength(uint32) uint32 {
-	// 32 + (8 * 4) + (4 * 1) + (2 * 2) + (33 * 5)
-	return 237
+	// 32 + (8 * 4) + (4 * 1) + (2 * 2) + (33 * 6)
+	return 270
 }

lnwire/lnwire_test.go

@@ -188,6 +188,11 @@ func TestLightningWireProtocol(t *testing.T) {
 				t.Fatalf("unable to generate key: %v", err)
 				return
 			}
+			req.HtlcPoint, err = randPubKey()
+			if err != nil {
+				t.Fatalf("unable to generate key: %v", err)
+				return
+			}
 			req.FirstCommitmentPoint, err = randPubKey()
 			if err != nil {
 				t.Fatalf("unable to generate key: %v", err)
@@ -233,6 +238,11 @@ func TestLightningWireProtocol(t *testing.T) {
 				t.Fatalf("unable to generate key: %v", err)
 				return
 			}
+			req.HtlcPoint, err = randPubKey()
+			if err != nil {
+				t.Fatalf("unable to generate key: %v", err)
+				return
+			}
 			req.FirstCommitmentPoint, err = randPubKey()
 			if err != nil {
 				t.Fatalf("unable to generate key: %v", err)

lnwire/open_channel.go

@@ -102,6 +102,12 @@ type OpenChannel struct {
 	// where they claim funds.
 	DelayedPaymentPoint *btcec.PublicKey
 
+	// HtlcPoint is the base point used to derive the set of keys for this
+	// party that will be used within the HTLC public key scripts.  This
+	// value is combined with the receiver's revocation base point in order
+	// to derive the keys that are used within HTLC scripts.
+	HtlcPoint *btcec.PublicKey
+
 	// FirstCommitmentPoint is the first commitment point for the sending
 	// party. This value should be combined with the receiver's revocation
 	// base point in order to derive the revocation keys that are placed
@@ -141,6 +147,7 @@ func (o *OpenChannel) Encode(w io.Writer, pver uint32) error {
 		o.RevocationPoint,
 		o.PaymentPoint,
 		o.DelayedPaymentPoint,
+		o.HtlcPoint,
 		o.FirstCommitmentPoint,
 		o.ChannelFlags,
 	)
@@ -168,6 +175,7 @@ func (o *OpenChannel) Decode(r io.Reader, pver uint32) error {
 		&o.RevocationPoint,
 		&o.PaymentPoint,
 		&o.DelayedPaymentPoint,
+		&o.HtlcPoint,
 		&o.FirstCommitmentPoint,
 		&o.ChannelFlags,
 	)
@@ -186,6 +194,6 @@ func (o *OpenChannel) MsgType() MessageType {
 //
 // This is part of the lnwire.Message interface.
 func (o *OpenChannel) MaxPayloadLength(uint32) uint32 {
-	// (32 * 2) + (8 * 6) + (4 * 1) + (2 * 2) + (33 * 5) + 1
-	return 286
+	// (32 * 2) + (8 * 6) + (4 * 1) + (2 * 2) + (33 * 6) + 1
+	return 319
 }