netann: validation and verification funcs for ChannelAnnouncement2

netann/channel_announcement.go

@@ -6,9 +6,26 @@ import (
 	"fmt"
 
 	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/lightningnetwork/lnd/channeldb/models"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+const (
+	// chanAnn2MsgName is a string representing the name of the
+	// ChannelAnnouncement2 message. This string will be used during the
+	// construction of the tagged hash message to be signed when producing
+	// the signature for the ChannelAnnouncement2 message.
+	chanAnn2MsgName = "channel_announcement_2"
+
+	// chanAnn2SigFieldName is the name of the signature field of the
+	// ChannelAnnouncement2 message. This string will be used during the
+	// construction of the tagged hash message to be signed when producing
+	// the signature for the ChannelAnnouncement2 message.
+	chanAnn2SigFieldName = "signature"
 )
 
 // CreateChanAnnouncement is a helper function which creates all channel
@@ -94,10 +111,14 @@ func CreateChanAnnouncement(chanProof *models.ChannelAuthProof,
 type FetchPkScript func(*lnwire.ShortChannelID) ([]byte, error)
 
 // ValidateChannelAnn validates the channel announcement.
-func ValidateChannelAnn(a lnwire.ChannelAnnouncement, _ FetchPkScript) error {
+func ValidateChannelAnn(a lnwire.ChannelAnnouncement,
+	fetchPkScript FetchPkScript) error {
+
 	switch ann := a.(type) {
 	case *lnwire.ChannelAnnouncement1:
 		return validateChannelAnn1(ann)
+	case *lnwire.ChannelAnnouncement2:
+		return validateChannelAnn2(ann, fetchPkScript)
 	default:
 		return fmt.Errorf("unhandled implementation of "+
 			"lnwire.ChannelAnnouncement: %T", a)
@@ -175,3 +196,96 @@ func validateChannelAnn1(a *lnwire.ChannelAnnouncement1) error {
 
 	return nil
 }
+
+// validateChannelAnn2 validates the channel announcement message and checks
+// that message signature covers the announcement message.
+func validateChannelAnn2(a *lnwire.ChannelAnnouncement2,
+	fetchPkScript FetchPkScript) error {
+
+	dataHash, err := ChanAnn2DigestToSign(a)
+	if err != nil {
+		return err
+	}
+
+	sig, err := a.Signature.ToSignature()
+	if err != nil {
+		return err
+	}
+
+	nodeKey1, err := btcec.ParsePubKey(a.NodeID1.Val[:])
+	if err != nil {
+		return err
+	}
+
+	nodeKey2, err := btcec.ParsePubKey(a.NodeID2.Val[:])
+	if err != nil {
+		return err
+	}
+
+	keys := []*btcec.PublicKey{
+		nodeKey1, nodeKey2,
+	}
+
+	// If the bitcoin keys are provided in the announcement, then it is
+	// assumed that the signature of the announcement is a 4-of-4 MuSig2
+	// over the bitcoin keys and node ID keys.
+	if a.BitcoinKey1.IsSome() && a.BitcoinKey2.IsSome() {
+		var (
+			btcKey1 tlv.RecordT[tlv.TlvType12, [33]byte]
+			btcKey2 tlv.RecordT[tlv.TlvType14, [33]byte]
+		)
+
+		btcKey1 = a.BitcoinKey1.UnwrapOr(btcKey1)
+		btcKey2 = a.BitcoinKey2.UnwrapOr(btcKey2)
+
+		bitcoinKey1, err := btcec.ParsePubKey(btcKey1.Val[:])
+		if err != nil {
+			return err
+		}
+
+		bitcoinKey2, err := btcec.ParsePubKey(btcKey2.Val[:])
+		if err != nil {
+			return err
+		}
+
+		keys = append(keys, bitcoinKey1, bitcoinKey2)
+	} else {
+		// If bitcoin keys are not provided, then we need to get the
+		// on-chain output key since this will be the 3rd key in the
+		// 3-of-3 MuSig2 signature.
+		pkScript, err := fetchPkScript(&a.ShortChannelID.Val)
+		if err != nil {
+			return err
+		}
+
+		outputKey, err := schnorr.ParsePubKey(pkScript[2:])
+		if err != nil {
+			return err
+		}
+
+		keys = append(keys, outputKey)
+	}
+
+	aggKey, _, _, err := musig2.AggregateKeys(keys, true)
+	if err != nil {
+		return err
+	}
+
+	if !sig.Verify(dataHash.CloneBytes(), aggKey.FinalKey) {
+		return fmt.Errorf("invalid sig")
+	}
+
+	return nil
+}
+
+// ChanAnn2DigestToSign computes the digest of the message to be signed.
+func ChanAnn2DigestToSign(a *lnwire.ChannelAnnouncement2) (*chainhash.Hash,
+	error) {
+
+	data, err := a.DataToSign()
+	if err != nil {
+		return nil, err
+	}
+
+	return MsgHash(chanAnn2MsgName, chanAnn2SigFieldName, data), nil
+}