diff --git a/go/common/crypto/signature/signers/remote/grpc.go b/go/common/crypto/signature/signers/remote/grpc.go
index cebd48b5f65..1a9ee9847e8 100644
--- a/go/common/crypto/signature/signers/remote/grpc.go
+++ b/go/common/crypto/signature/signers/remote/grpc.go
@@ -26,7 +26,7 @@ var (
 
 	serviceDesc = grpc.ServiceDesc{
 		ServiceName: string(serviceName),
-		HandlerType: (*wrapper)(nil),
+		HandlerType: (*Backend)(nil),
 		Methods: []grpc.MethodDesc{
 			{
 				MethodName: methodPublicKeys.ShortName(),
@@ -53,11 +53,17 @@ type SignRequest struct {
 	Message []byte               `json:"message"`
 }
 
+// Backend is the remote signer backend interface.
+type Backend interface {
+	PublicKeys(context.Context) ([]PublicKey, error)
+	Sign(context.Context, *SignRequest) ([]byte, error)
+}
+
 type wrapper struct {
 	signers map[signature.SignerRole]signature.Signer
 }
 
-func (w *wrapper) publicKeys(ctx context.Context) ([]PublicKey, error) {
+func (w *wrapper) PublicKeys(ctx context.Context) ([]PublicKey, error) {
 	var resp []PublicKey
 	for _, v := range signature.SignerRoles { // Return in consistent order.
 		if signer := w.signers[v]; signer != nil {
@@ -70,7 +76,7 @@ func (w *wrapper) publicKeys(ctx context.Context) ([]PublicKey, error) {
 	return resp, nil
 }
 
-func (w *wrapper) sign(ctx context.Context, req *SignRequest) ([]byte, error) {
+func (w *wrapper) Sign(ctx context.Context, req *SignRequest) ([]byte, error) {
 	signer, ok := w.signers[req.Role]
 	if !ok {
 		return nil, signature.ErrNotExist
@@ -85,14 +91,14 @@ func handlerPublicKeys( // nolint: golint
 	interceptor grpc.UnaryServerInterceptor,
 ) (interface{}, error) {
 	if interceptor == nil {
-		return srv.(*wrapper).publicKeys(ctx)
+		return srv.(Backend).PublicKeys(ctx)
 	}
 	info := &grpc.UnaryServerInfo{
 		Server:     srv,
 		FullMethod: methodPublicKeys.FullName(),
 	}
 	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
-		return srv.(*wrapper).publicKeys(ctx)
+		return srv.(Backend).PublicKeys(ctx)
 	}
 	return interceptor(ctx, nil, info, handler)
 }
@@ -108,14 +114,14 @@ func handlerSign( // nolint: golint
 		return nil, err
 	}
 	if interceptor == nil {
-		return srv.(*wrapper).sign(ctx, &req)
+		return srv.(Backend).Sign(ctx, &req)
 	}
 	info := &grpc.UnaryServerInfo{
 		Server:     srv,
 		FullMethod: methodSign.FullName(),
 	}
 	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
-		return srv.(*wrapper).sign(ctx, req.(*SignRequest))
+		return srv.(Backend).Sign(ctx, req.(*SignRequest))
 	}
 	return interceptor(ctx, &req, info, handler)
 }
@@ -137,6 +143,7 @@ func RegisterService(server *grpc.Server, signerFactory signature.SignerFactory)
 			w.signers[v] = signer
 		}
 	}
+
 	server.RegisterService(&serviceDesc, w)
 }