python-tuf/tests/test_arbitrary_package_attack.py

#!/usr/bin/env python

"""
<Program Name>
  test_arbitrary_package_attack.py

<Author>
  Konstantin Andrianov.

<Started>
  February 22, 2012.

  March 21, 2014.
    Refactored to use the 'unittest' module (test conditions in code, rather
    than verifying text output), use pre-generated repository files, and
    discontinue use of the old repository tools. -vladimir.v.diaz

<Copyright>
  See LICENSE for licensing information.

<Purpose>
  Simulate an arbitrary package attack, where an updater client attempts to
  download a malicious file.  TUF and non-TUF client scenarios are tested.  

  There is no difference between 'updates' and 'target' files.
"""

# Help with Python 3 compatibility, where the print statement is a function, an
# implicit relative import is invalid, and the '/' operator performs true
# division.  Example:  print 'hello world' raises a 'SyntaxError' exception.
from __future__ import print_function
from __future__ import absolute_import
from __future__ import division
from __future__ import unicode_literals

import os
import tempfile
import random
import time
import shutil
import json
import subprocess
import logging
import sys

# 'unittest2' required for testing under Python < 2.7.
if sys.version_info >= (2, 7):
  import unittest

else:
  import unittest2 as unittest 

import tuf
import tuf.formats
import tuf.util
import tuf.log
import tuf.client.updater as updater
import tuf.unittest_toolbox as unittest_toolbox
import tuf._vendor.six as six

logger = logging.getLogger('tuf.test_arbitrary_package_attack')


class TestArbitraryPackageAttack(unittest_toolbox.Modified_TestCase):

  @classmethod
  def setUpClass(cls):
    # setUpClass() is called before any of the test cases are executed.
    
    # Create a temporary directory to store the repository, metadata, and target
    # files.  'temporary_directory' must be deleted in TearDownModule() so that
    # temporary files are always removed, even when exceptions occur. 
    cls.temporary_directory = tempfile.mkdtemp(dir=os.getcwd())
    
    # Launch a SimpleHTTPServer (serves files in the current directory).
    # Test cases will request metadata and target files that have been
    # pre-generated in 'tuf/tests/repository_data', which will be served by the
    # SimpleHTTPServer launched here.  The test cases of this unit test assume 
    # the pre-generated metadata files have a specific structure, such
    # as a delegated role 'targets/role1', three target files, five key files,
    # etc.
    cls.SERVER_PORT = random.randint(30000, 45000)
    command = ['python', 'simple_server.py', str(cls.SERVER_PORT)]
    cls.server_process = subprocess.Popen(command, stderr=subprocess.PIPE)
    logger.info('Server process started.')
    logger.info('Server process id: '+str(cls.server_process.pid))
    logger.info('Serving on port: '+str(cls.SERVER_PORT))
    cls.url = 'http://localhost:'+str(cls.SERVER_PORT) + os.path.sep

    # NOTE: Following error is raised if a delay is not applied:
    # <urlopen error [Errno 111] Connection refused>
    time.sleep(1)



  @classmethod 
  def tearDownClass(cls):
    # tearDownModule() is called after all the test cases have run.
    # http://docs.python.org/2/library/unittest.html#class-and-module-fixtures
   
    # Remove the temporary repository directory, which should contain all the
    # metadata, targets, and key files generated of all the test cases.
    shutil.rmtree(cls.temporary_directory)
   
    # Kill the SimpleHTTPServer process.
    if cls.server_process.returncode is None:
      logger.info('Server process '+str(cls.server_process.pid)+' terminated.')
      cls.server_process.kill()



  def setUp(self):
    # We are inheriting from custom class.
    unittest_toolbox.Modified_TestCase.setUp(self)
  
    # Copy the original repository files provided in the test folder so that
    # any modifications made to repository files are restricted to the copies.
    # The 'repository_data' directory is expected to exist in 'tuf/tests/'.
    original_repository_files = os.path.join(os.getcwd(), 'repository_data') 
    temporary_repository_root = \
      self.make_temp_directory(directory=self.temporary_directory)
  
    # The original repository, keystore, and client directories will be copied
    # for each test case. 
    original_repository = os.path.join(original_repository_files, 'repository')
    original_client = os.path.join(original_repository_files, 'client')

    # Save references to the often-needed client repository directories.
    # Test cases need these references to access metadata and target files. 
    self.repository_directory = \
      os.path.join(temporary_repository_root, 'repository')
    self.client_directory = os.path.join(temporary_repository_root, 'client')

    # Copy the original 'repository', 'client', and 'keystore' directories
    # to the temporary repository the test cases can use.
    shutil.copytree(original_repository, self.repository_directory)
    shutil.copytree(original_client, self.client_directory)

    # Set the url prefix required by the 'tuf/client/updater.py' updater.
    # 'path/to/tmp/repository' -> 'localhost:8001/tmp/repository'. 
    repository_basepath = self.repository_directory[len(os.getcwd()):]
    url_prefix = \
      'http://localhost:' + str(self.SERVER_PORT) + repository_basepath 
    
    # Setting 'tuf.conf.repository_directory' with the temporary client
    # directory copied from the original repository files.
    tuf.conf.repository_directory = self.client_directory 
    self.repository_mirrors = {'mirror1': {'url_prefix': url_prefix,
                                           'metadata_path': 'metadata',
                                           'targets_path': 'targets',
                                           'confined_target_dirs': ['']}}

    # Create the repository instance.  The test cases will use this client
    # updater to refresh metadata, fetch target files, etc.
    self.repository_updater = updater.Updater('test_repository',
                                              self.repository_mirrors)


  def tearDown(self):
    # Modified_TestCase.tearDown() automatically deletes temporary files and
    # directories that may have been created during each test case.
    unittest_toolbox.Modified_TestCase.tearDown(self)



  def test_without_tuf(self):
    # Verify that a target file replaced with a malicious version is downloaded
    # by a non-TUF client (i.e., a non-TUF client that does not verify hashes,
    # detect mix-and-mix attacks, etc.)  A tuf client, on the other hand, should
    # detect that the downloaded target file is invalid.
   
    # Test: Download a valid target file from the repository.
    # Ensure the target file to be downloaded has not already been downloaded,
    # and generate its file size and digest.  The file size and digest is needed
    # to check that the malicious file was indeed downloaded.
    target_path = os.path.join(self.repository_directory, 'targets', 'file1.txt')
    client_target_path = os.path.join(self.client_directory, 'file1.txt') 
    self.assertFalse(os.path.exists(client_target_path))
    length, hashes = tuf.util.get_file_details(target_path)
    fileinfo = tuf.formats.make_fileinfo(length, hashes)
    
    url_prefix = self.repository_mirrors['mirror1']['url_prefix']
    url_file = os.path.join(url_prefix, 'targets', 'file1.txt')
    six.moves.urllib.request.urlretrieve(url_file, client_target_path)
    
    self.assertTrue(os.path.exists(client_target_path))
    length, hashes = tuf.util.get_file_details(client_target_path)
    download_fileinfo = tuf.formats.make_fileinfo(length, hashes)
    self.assertEqual(fileinfo, download_fileinfo)
  
    # Test: Download a target file that has been modified by an attacker.
    with open(target_path, 'wt') as file_object:
      file_object.write('add malicious content.')
    length, hashes = tuf.util.get_file_details(target_path)
    malicious_fileinfo = tuf.formats.make_fileinfo(length, hashes)
    
    six.moves.urllib.request.urlretrieve(url_file, client_target_path)
    
    length, hashes = tuf.util.get_file_details(client_target_path)
    download_fileinfo = tuf.formats.make_fileinfo(length, hashes)
    
    # Verify 'download_fileinfo' is unequal to the original trusted version.
    self.assertNotEqual(download_fileinfo, fileinfo)

    # Verify 'download_fileinfo' is equal to the malicious version.
    self.assertEqual(download_fileinfo, malicious_fileinfo)



  def test_with_tuf(self):
    # Verify that a target file (on the remote repository) modified by an
    # attacker is not downloaded by the TUF client.
    # First test that the valid target file is successfully downloaded.
    file1_fileinfo = self.repository_updater.target('file1.txt')
    destination = os.path.join(self.client_directory)
    self.repository_updater.download_target(file1_fileinfo, destination)
    client_target_path = os.path.join(destination, 'file1.txt')
    self.assertTrue(os.path.exists(client_target_path))

    # Modify 'file1.txt' and confirm that the TUF client rejects it.
    target_path = os.path.join(self.repository_directory, 'targets', 'file1.txt')
    with open(target_path, 'wt') as file_object:
      file_object.write('add malicious content.')

    try:
      self.repository_updater.download_target(file1_fileinfo, destination)
    
    except tuf.NoWorkingMirrorError as exception:
      url_prefix = self.repository_mirrors['mirror1']['url_prefix']
      url_file = os.path.join(url_prefix, 'targets', 'file1.txt')

      # Verify that only one exception is raised for 'url_file'.
      self.assertTrue(len(exception.mirror_errors), 1)

      # Verify that the expected 'tuf.DownloadLengthMismatchError' exception
      # is raised for 'url_file'.
      self.assertTrue(url_file in exception.mirror_errors)
      self.assertTrue(isinstance(exception.mirror_errors[url_file],
                                 tuf.DownloadLengthMismatchError))
    
    else:
      self.fail('TUF did not prevent an arbitrary package attack.')
  
  
  def test_with_tuf_and_metadata_tampering(self):
    # Test that a TUF client does not download a malicious target file, and a
    # 'targets.json' metadata file that has also been modified by the attacker.
    # The attacker does not attach a valid signature to 'targets.json'
    
    # An attacker modifies 'file1.txt'.
    target_path = os.path.join(self.repository_directory, 'targets', 'file1.txt')
    with open(target_path, 'wt') as file_object:
      file_object.write('add malicious content.')

    # An attacker also tries to add the malicious target's length and digest
    # to its metadata file.
    length, hashes = tuf.util.get_file_details(target_path)

    metadata_path = \
      os.path.join(self.repository_directory, 'metadata', 'targets.json')
    
    metadata = tuf.util.load_json_file(metadata_path)
    metadata['signed']['targets']['/file1.txt']['hashes'] = hashes
    metadata['signed']['targets']['/file1.txt']['length'] = length

    tuf.formats.check_signable_object_format(metadata) 
    
    with open(metadata_path, 'wb') as file_object:
      json.dumps(metadata, file_object, indent=1, sort_keys=True).encode('utf-8')   
   
    # Verify that the malicious 'targets.json' is not downloaded.  Perform
    # a refresh of top-level metadata to demonstrate that the malicious
    # 'targets.json' is not downloaded.
    try:
      self.repository_updater.refresh()
      file1_fileinfo = self.repository_updater.target('file1.txt')
      destination = os.path.join(self.client_directory)
      self.repository_updater.download_target(file1_fileinfo, destination)
    
    except tuf.NoWorkingMirrorError as exception:
      url_prefix = self.repository_mirrors['mirror1']['url_prefix']
      url_file = os.path.join(url_prefix, 'targets', 'file1.txt')

      # Verify that an exception raised for only the malicious 'url_file'.
      self.assertTrue(len(exception.mirror_errors), 1)

      # Verify that the specific and expected mirror exception is raised.
      self.assertTrue(url_file in exception.mirror_errors)
      self.assertTrue(isinstance(exception.mirror_errors[url_file],
                                 tuf.DownloadLengthMismatchError))
    
    else:
      self.fail('TUF did not prevent an arbitrary package attack.')


if __name__ == '__main__':
  unittest.main()