text: #!/usr/bin/python
  # Copyright 2015 The Chromium OS Authors. All rights reserved.
  # Use of this source code is governed by a BSD-style license that can be
  # found in the LICENSE file.
  
  """Module for testing cryptography functions using extended commands."""
  
  from __future__ import print_function
  
  import binascii
  import struct
  import xml.etree.ElementTree as ET
  
  import subcmd
  import utils
  
  # Basic crypto operations
  DECRYPT = 0
  ENCRYPT = 1
  
  def get_attribute(tdesc, attr_name, required=True):
    """Retrieve an attribute value from an XML node.
  
    Args:
      tdesc: an Element of the ElementTree, a test descriptor containing
        necessary information to run a single encryption/description
        session.
      attr_name: a string, the name of the attribute to retrieve.
      required: a Boolean, if True - the attribute must be present in the
        descriptor, otherwise it is considered optional
    Returns:
      The attribute value as a string (ascii or binary)
    Raises:
      subcmd.TpmTestError: on various format errors, or in case a required
        attribute is not found, the error message describes the problem.
  
    """
    # Fields stored in hex format by default.
    default_hex = ('aad', 'cipher_text', 'iv', 'key', 'tag')
  
    data = tdesc.find(attr_name)
    if data is None:
      if required:
        raise subcmd.TpmTestError('node "%s" does not have attribute "%s"' %
                          (tdesc.get('name'), attr_name))
      return ''
  
    # Attribute is present, does it have to be decoded from hex?
    cell_format = data.get('format')
    if not cell_format:
      if attr_name in default_hex:
        cell_format = 'hex'
      else:
        cell_format = 'ascii'
    elif cell_format not in ('hex', 'ascii'):
      raise subcmd.TpmTestError('%s:%s, unrecognizable format "%s"' %
                        (tdesc.get('name'), attr_name, cell_format))
  
    text = ' '.join(x.strip() for x in data.text.splitlines() if x)
    if cell_format == 'ascii':
      return text
  
    # Drop spaces from hex representation.
    text = text.replace(' ', '')
  
    # Convert hex-text to little-endian binary (in 4-byte word chunks)
    value = ''
    for x in range(len(text)/8):
      try:
        value += struct.pack('<I', int('0x%s' % text[8*x:8*(x+1)], 16))
      except ValueError:
        raise subcmd.TpmTestError('%s:%s %swrong hex value' %
                          (tdesc.get('name'), attr_name, utils.hex_dump(text)))
  
    # Unpack remaining hex text, without introducing a zero pad.
    for x in range(-1, -(len(text) % 8), -1):
      value += chr(int(text[2*x:len(text) + (2*x)+2], 16))
  
    return value
  
  
  class CryptoD(object):
    """A helper object to contain an encryption scheme description.
  
    Attributes:
      subcmd: a 16 bit max integer, the extension subcommand to be used with
        this encryption scheme.
      sumbodes: an optional dictionary, the keys are strings, names of the
        encryption scheme submodes, the values are integers to be included in
        the appropriate subcommand fields to communicat the submode to the
        device.
    """
  
    def __init__(self, subcommand, submodes=None):
      self.subcmd = subcommand
      if not submodes:
        submodes = {}
      self.submodes = submodes
  
  SUPPORTED_MODES = {
      'AES': CryptoD(subcmd.AES, {
          'ECB': 0,
          'CTR': 1,
          'CBC': 2,
          'GCM': 3,
          'OFB': 4,
          'CFB': 5
      }),
  }
  
  def crypto_run(node_name, op_type, key, iv, aad, in_text, out_text, tpm):
    """Perform a basic operation(encrypt or decrypt).
  
    This function creates an extended command with the requested parameters,
    sends it to the device, and then compares the response to the expected
    value.
  
    Args:
      node_name: a string, the name of the XML node this data comes from. The
        format of the name is "<enc type>:<submode> ....", where <enc type> is
        the major encryption mode (say AED or DES) and submode - a variant of
        the major scheme, if exists.
  
     op_type: an int, encodes the operation to perform (encrypt/decrypt), passed
       directly to the device as a field in the extended command
     key: a binary string
     iv: a binary string, might be empty
     aad: additional authenticated data
     in_text: a binary string, the input of the encrypt/decrypt operation
     out_text: a binary string, might be empty, the expected output of the
       operation. Note that it could be shorter than actual output (padded to
       integer number of blocks), in which case only its length of bytes is
       compared debug_mode: a Boolean, if True - enables tracing on the console
     tpm: a TPM object to send extended commands to an initialized TPM
  
    Returns:
      The actual binary string, result of the operation, if the
      comparison with the expected value was successful.
  
    Raises:
      subcmd.TpmTestError: in case there were problems parsing the node name, or
        verifying the operation results.
  
    """
    mode_name, submode_name = node_name.split(':')
    submode_name = submode_name[:3].upper()
  
    mode = SUPPORTED_MODES.get(mode_name.upper())
    if not mode:
      raise subcmd.TpmTestError('unrecognizable mode in node "%s"' % node_name)
  
    submode = mode.submodes.get(submode_name, 0)
    cmd = '%c' % op_type    # Encrypt or decrypt
    cmd += '%c' % submode   # A particular type of a generic algorithm.
    cmd += '%c' % len(key)
    cmd += key
    cmd += '%c' % len(iv)
    if iv:
      cmd += iv
    cmd += '%c' % len(aad)
    if aad:
      cmd += aad
    cmd += struct.pack('>H', len(in_text))
    cmd += in_text
    if tpm.debug_enabled():
      print('%d:%d cmd size' % (op_type, mode.subcmd),
            len(cmd), utils.hex_dump(cmd))
    wrapped_response = tpm.command(tpm.wrap_ext_command(mode.subcmd, cmd))
    real_out_text = tpm.unwrap_ext_response(mode.subcmd, wrapped_response)
    if out_text:
      if len(real_out_text) > len(out_text):
        real_out_text = real_out_text[:len(out_text)]  # Ignore padding
      if real_out_text != out_text:
        if tpm.debug_enabled():
          print('Out text mismatch in node %s:\n' % node_name)
        else:
          raise subcmd.TpmTestError(
            'Out text mismatch in node %s, operation %s:\n'
            'In text:%sExpected out text:%sReal out text:%s' % (
              node_name, 'ENCRYPT' if op_type == ENCRYPT else 'DECRYPT',
              utils.hex_dump(in_text),
              utils.hex_dump(out_text),
              utils.hex_dump(real_out_text)))
    return real_out_text
  
  
  def crypto_test(tdesc, tpm):
    """Perform a single test described in the xml file.
  
    The xml node contains all pertinent information about the test inputs and
    outputs.
  
    Args:
      tdesc: an Element of the ElementTree, a test descriptor containing
        necessary information to run a single encryption/description
        session.
      tpm: a TPM object to send extended commands to an initialized TPM
    Raises:
      subcmd.TpmTestError: on various execution errors, the details are included
        in the error message.
  
    """
    node_name = tdesc.get('name')
    key = get_attribute(tdesc, 'key')
    if len(key) not in (16, 24, 32):
      raise subcmd.TpmTestError('wrong key size "%s:%s"' % (
          node_name,
          ''.join('%2.2x' % ord(x) for x in key)))
    iv = get_attribute(tdesc, 'iv', required=False)
    if iv and not node_name.startswith('AES:GCM') and len(iv) != 16:
      raise subcmd.TpmTestError('wrong iv size "%s:%s"' % (
          node_name,
          ''.join('%2.2x' % ord(x) for x in iv)))
    clear_text = get_attribute(tdesc, 'clear_text', required=False)
    if clear_text:
      clear_text_len = get_attribute(tdesc, 'clear_text_len', required=False)
      if clear_text_len:
        clear_text = clear_text[:int(clear_text_len)]
    else:
      clear_text_len = None
    if tpm.debug_enabled():
      print('clear text size', len(clear_text))
    cipher_text = get_attribute(tdesc, 'cipher_text', required=False)
    if clear_text_len:
      cipher_text = cipher_text[:int(clear_text_len)]
    tag = get_attribute(tdesc, 'tag', required=False)
    aad = get_attribute(tdesc, 'aad', required=False)
    if aad:
      aad_len = get_attribute(tdesc, 'aad_len', required=False)
      if aad_len:
        aad = aad[:int(aad_len)]
    real_cipher_text = crypto_run(node_name, ENCRYPT, key, iv,
                                  aad or '', clear_text, cipher_text + tag, tpm)
    crypto_run(node_name, DECRYPT, key, iv, aad or '',
               real_cipher_text[:len(real_cipher_text) - len(tag)],
               clear_text + tag, tpm)
    print(utils.cursor_back() + 'SUCCESS: %s' % node_name)
  
  def crypto_tests(tpm, xml_file):
    tree = ET.parse(xml_file)
    root = tree.getroot()
    for child in root:
      crypto_test(child, tpm)
  