ff1_fpe code based on https://github.com/capitalone/fpe
License as follows:
/*
SPDX-Copyright: Copyright (c) Capital One Services, LLC
SPDX-License-Identifier: Apache-2.0
Copyright 2017 Capital One Services, LLC
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and limitations under the License.
*/