notification signature is a lightning signed msg

go.mod

@@ -156,6 +156,7 @@ require (
 	github.com/stretchr/objx v0.5.0 // indirect
 	github.com/syndtr/goleveldb v1.0.1-0.20210819022825-2ae1ddf74ef7 // indirect
 	github.com/tmc/grpc-websocket-proxy v0.0.0-20201229170055-e5319fda7802 // indirect
+	github.com/tv42/zbase32 v0.0.0-20220222190657-f76a9fc892fa
 	github.com/ulikunitz/xz v0.5.10 // indirect
 	github.com/wk8/go-ordered-map/v2 v2.1.8
 	github.com/xi2/xz v0.0.0-20171230120015-48954b6210f8 // indirect

itest/lspd_node.go

@@ -16,6 +16,7 @@ import (
 
 	"github.com/breez/lntest"
 	"github.com/breez/lspd/config"
+	"github.com/breez/lspd/lightning"
 	"github.com/breez/lspd/notifications"
 	lspd "github.com/breez/lspd/rpc"
 	"github.com/btcsuite/btcd/btcec/v2"
@@ -24,6 +25,7 @@ import (
 	ecies "github.com/ecies/go/v2"
 	"github.com/golang/protobuf/proto"
 	"github.com/stretchr/testify/assert"
+	"github.com/tv42/zbase32"
 	"google.golang.org/grpc/metadata"
 )
 
@@ -290,14 +292,14 @@ func RegisterPayment(l LspNode, paymentInfo *lspd.PaymentInformation, continueOn
 }
 
 func SubscribeNotifications(l LspNode, b BreezClient, url string, continueOnError bool) error {
-	first := sha256.Sum256([]byte(url))
+	msg := append(lightning.SignedMsgPrefix, []byte(url)...)
+	first := sha256.Sum256([]byte(msg))
 	second := sha256.Sum256(first[:])
 	sig, err := ecdsa.SignCompact(b.Node().PrivateKey(), second[:], true)
 	assert.NoError(b.Harness().T, err)
-
 	request := notifications.SubscribeNotificationsRequest{
 		Url:       url,
-		Signature: sig,
+		Signature: zbase32.EncodeToString(sig),
 	}
 	serialized, err := proto.Marshal(&request)
 	lntest.CheckError(l.Harness().T, err)

lightning/verify_message.go

@@ -0,0 +1,38 @@
+package lightning
+
+import (
+	"crypto/sha256"
+	"fmt"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/ecdsa"
+	"github.com/tv42/zbase32"
+)
+
+var ErrInvalidSignature = fmt.Errorf("invalid signature")
+var SignedMsgPrefix = []byte("Lightning Signed Message:")
+
+func VerifyMessage(message []byte, signature string) (*btcec.PublicKey, error) {
+	// The signature should be zbase32 encoded
+	sig, err := zbase32.DecodeString(signature)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode signature: %v", err)
+	}
+
+	msg := append(SignedMsgPrefix, message...)
+	first := sha256.Sum256(msg)
+	second := sha256.Sum256(first[:])
+	pubkey, wasCompressed, err := ecdsa.RecoverCompact(
+		sig,
+		second[:],
+	)
+	if err != nil {
+		return nil, ErrInvalidSignature
+	}
+
+	if !wasCompressed {
+		return nil, ErrInvalidSignature
+	}
+
+	return pubkey, nil
+}

notifications/notifications.pb.go

@@ -73,7 +73,7 @@ type SubscribeNotificationsRequest struct {
 	unknownFields protoimpl.UnknownFields
 
 	Url       string `protobuf:"bytes,1,opt,name=url,proto3" json:"url,omitempty"`
-	Signature []byte `protobuf:"bytes,2,opt,name=signature,proto3" json:"signature,omitempty"`
+	Signature string `protobuf:"bytes,2,opt,name=signature,proto3" json:"signature,omitempty"`
 }
 
 func (x *SubscribeNotificationsRequest) Reset() {
@@ -115,11 +115,11 @@ func (x *SubscribeNotificationsRequest) GetUrl() string {
 	return ""
 }
 
-func (x *SubscribeNotificationsRequest) GetSignature() []byte {
+func (x *SubscribeNotificationsRequest) GetSignature() string {
 	if x != nil {
 		return x.Signature
 	}
-	return nil
+	return ""
 }
 
 type SubscribeNotificationsReply struct {
@@ -172,7 +172,7 @@ var file_notifications_proto_rawDesc = []byte{
 	0x63, 0x72, 0x69, 0x62, 0x65, 0x4e, 0x6f, 0x74, 0x69, 0x66, 0x69, 0x63, 0x61, 0x74, 0x69, 0x6f,
 	0x6e, 0x73, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x12, 0x10, 0x0a, 0x03, 0x75, 0x72, 0x6c,
 	0x18, 0x01, 0x20, 0x01, 0x28, 0x09, 0x52, 0x03, 0x75, 0x72, 0x6c, 0x12, 0x1c, 0x0a, 0x09, 0x73,
-	0x69, 0x67, 0x6e, 0x61, 0x74, 0x75, 0x72, 0x65, 0x18, 0x02, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x09,
+	0x69, 0x67, 0x6e, 0x61, 0x74, 0x75, 0x72, 0x65, 0x18, 0x02, 0x20, 0x01, 0x28, 0x09, 0x52, 0x09,
 	0x73, 0x69, 0x67, 0x6e, 0x61, 0x74, 0x75, 0x72, 0x65, 0x22, 0x1d, 0x0a, 0x1b, 0x53, 0x75, 0x62,
 	0x73, 0x63, 0x72, 0x69, 0x62, 0x65, 0x4e, 0x6f, 0x74, 0x69, 0x66, 0x69, 0x63, 0x61, 0x74, 0x69,
 	0x6f, 0x6e, 0x73, 0x52, 0x65, 0x70, 0x6c, 0x79, 0x32, 0x84, 0x01, 0x0a, 0x0d, 0x4e, 0x6f, 0x74,

notifications/notifications.proto

@@ -15,7 +15,7 @@ message EncryptedNotificationRequest {
 
 message SubscribeNotificationsRequest {
     string url = 1;
-    bytes signature = 2;
+    string signature = 2;
 }
 
 message SubscribeNotificationsReply {

notifications/server.go

@@ -2,18 +2,16 @@ package notifications
 
 import (
 	context "context"
-	"crypto/sha256"
 	"encoding/hex"
 	"fmt"
 	"log"
 
+	"github.com/breez/lspd/lightning"
 	lspdrpc "github.com/breez/lspd/rpc"
-	"github.com/btcsuite/btcd/btcec/v2/ecdsa"
 	ecies "github.com/ecies/go/v2"
 	"github.com/golang/protobuf/proto"
 )
 
-var ErrInvalidSignature = fmt.Errorf("invalid signature")
 var ErrInternal = fmt.Errorf("internal error")
 
 type server struct {
@@ -48,18 +46,9 @@ func (s *server) SubscribeNotifications(
 		return nil, fmt.Errorf("proto.Unmarshal(%x) error: %w", data, err)
 	}
 
-	first := sha256.Sum256([]byte(request.Url))
-	second := sha256.Sum256(first[:])
-	pubkey, wasCompressed, err := ecdsa.RecoverCompact(
-		request.Signature,
-		second[:],
-	)
+	pubkey, err := lightning.VerifyMessage([]byte(request.Url), request.Signature)
 	if err != nil {
-		return nil, ErrInvalidSignature
-	}
-
-	if !wasCompressed {
-		return nil, ErrInvalidSignature
+		return nil, err
 	}
 
 	err = s.store.Register(ctx, hex.EncodeToString(pubkey.SerializeCompressed()), request.Url)