fix taproot address generation

x/lending/types/taproot.go

@@ -5,9 +5,13 @@ import (
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
 
+	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/txscript"
+
+	"github.com/sideprotocol/side/crypto/hash"
+	"github.com/sideprotocol/side/x/dlc/types"
 )
 
 func HashLoanSecret(secret string) string {
@@ -103,8 +107,9 @@ func createTaprootAddress(branches [][]byte, params *chaincfg.Params) (string, e
 	if err != nil {
 		return "", err
 	}
+
 	// Derive Taproot output key
-	taprootPubKey := txscript.ComputeTaprootOutputKey(nil, scriptRoot)
+	taprootPubKey := txscript.ComputeTaprootOutputKey(GetInternalKey(), scriptRoot)
 	// Generate Taproot address
 	address, err := btcutil.NewAddressTaproot(taprootPubKey.SerializeCompressed(), params)
 	if err != nil {
@@ -138,3 +143,19 @@ func CreateVaultAddress(borrowerPubkey string, dcaPubkey string, loanSecretHash
 	}
 	return taprootAddress, nil
 }
+
+// GetInternalKey gets the pub key used for taproot address generation
+// Generated by hash("lending") * G for now
+func GetInternalKey() *btcec.PublicKey {
+	hash := hash.Sha256([]byte(types.ModuleName))
+
+	var s btcec.ModNScalar
+	s.SetByteSlice(hash[:])
+
+	var p btcec.JacobianPoint
+	btcec.ScalarBaseMultNonConst(&s, &p)
+
+	p.ToAffine()
+
+	return btcec.NewPublicKey(&p.X, &p.Y)
+}