# Copyright 2019 Google Inc. All Rights Reserved. # # 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. # [START mac-example] """A command-line utility for checking file integrity with a Message Authentication Code (MAC). It loads cleartext keys from disk - this is not recommended! """ import binascii from absl import app from absl import flags from absl import logging import tink from tink import cleartext_keyset_handle from tink import mac FLAGS = flags.FLAGS flags.DEFINE_enum('mode', None, ['compute', 'verify'], 'The operation to perform.') flags.DEFINE_string('keyset_path', None, 'Path to the keyset used for the MAC operation.') flags.DEFINE_string('data_path', None, 'Path to the file with the input data to be checked.') flags.DEFINE_string('mac_path', None, 'Path to the file containing a hexadecimal MAC of the' ' data.') def main(argv): del argv # Unused. # Initialise Tink. mac.register() # Read the keyset into a keyset_handle. with open(FLAGS.keyset_path, 'rt') as keyset_file: try: text = keyset_file.read() keyset_handle = cleartext_keyset_handle.read(tink.JsonKeysetReader(text)) except tink.TinkError as e: logging.error('Error reading key: %s', e) return 1 # Get the primitive. try: primitive = keyset_handle.primitive(mac.Mac) except tink.TinkError as e: logging.error('Error creating primitive: %s', e) return 1 with open(FLAGS.data_path, 'rb') as data_file: data = data_file.read() if FLAGS.mode == 'compute': # Compute the MAC. tag = primitive.compute_mac(data) with open(FLAGS.mac_path, 'wb') as mac_file: mac_file.write(binascii.hexlify(tag)) return 0 with open(FLAGS.mac_path, 'rb') as mac_file: try: expected_tag = binascii.unhexlify(mac_file.read().strip()) except binascii.Error as e: logging.exception('Error reading expected tag: %s', e) return 1 try: primitive.verify_mac(expected_tag, data) logging.info('MAC verification succeeded.') return 0 except tink.TinkError as e: logging.info('MAC verification failed.') return 1 if __name__ == '__main__': flags.mark_flags_as_required([ 'mode', 'keyset_path', 'data_path', 'mac_path']) app.run(main) # [END mac-example]