text: #!/usr/bin/env python
  # Copyright 2016 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.
  
  """This module implements the low level device API.
  
  This module exposes a low level SecurityKey class,
  representing the physical security key device.
  """
  import logging
  
  from pyu2f import apdu
  from pyu2f import errors
  
  
  class SecurityKey(object):
    """Low level api for talking to a security key.
  
    This class implements the low level api specified in FIDO
    U2F for talking to a security key.
    """
  
    def __init__(self, transport):
      self.transport = transport
      self.use_legacy_format = False
      self.logger = logging.getLogger('pyu2f.hardware')
  
    def CmdRegister(self, challenge_param, app_param):
      """Register security key.
  
      Ask the security key to register with a particular origin & client.
  
      Args:
        challenge_param: Arbitrary 32 byte challenge string.
        app_param: Arbitrary 32 byte applciation parameter.
  
      Returns:
        A binary structure containing the key handle, attestation, and a
        signature over that by the attestation key.  The precise format
        is dictated by the FIDO U2F specs.
  
      Raises:
        TUPRequiredError: A Test of User Precense is required to proceed.
        ApduError: Something went wrong on the device.
      """
      self.logger.debug('CmdRegister')
      if len(challenge_param) != 32 or len(app_param) != 32:
        raise errors.InvalidRequestError()
  
      body = bytearray(challenge_param + app_param)
      response = self.InternalSendApdu(apdu.CommandApdu(
          0,
          apdu.CMD_REGISTER,
          0x03,  # Per the U2F reference code tests
          0x00,
          body))
      response.CheckSuccessOrRaise()
  
      return response.body
  
    def CmdAuthenticate(self,
                        challenge_param,
                        app_param,
                        key_handle,
                        check_only=False):
      """Attempt to obtain an authentication signature.
  
      Ask the security key to sign a challenge for a particular key handle
      in order to authenticate the user.
  
      Args:
        challenge_param: SHA-256 hash of client_data object as a bytes
            object.
        app_param: SHA-256 hash of the app id as a bytes object.
        key_handle: The key handle to use to issue the signature as a bytes
            object.
        check_only: If true, only check if key_handle is valid.
  
      Returns:
        A binary structure containing the key handle, attestation, and a
        signature over that by the attestation key.  The precise format
        is dictated by the FIDO U2F specs.
  
      Raises:
        TUPRequiredError: If check_only is False, a Test of User Precense
            is required to proceed.  If check_only is True, this means
            the key_handle is valid.
        InvalidKeyHandleError: The key_handle is not valid for this device.
        ApduError: Something else went wrong on the device.
      """
      self.logger.debug('CmdAuthenticate')
      if len(challenge_param) != 32 or len(app_param) != 32:
        raise errors.InvalidRequestError()
      control = 0x07 if check_only else 0x03
  
      body = bytearray(challenge_param + app_param +
                       bytearray([len(key_handle)]) + key_handle)
      response = self.InternalSendApdu(apdu.CommandApdu(
          0, apdu.CMD_AUTH, control, 0x00, body))
      response.CheckSuccessOrRaise()
  
      return response.body
  
    def CmdVersion(self):
      """Obtain the version of the device and test transport format.
  
      Obtains the version of the device and determines whether to use ISO
      7816-4 or the U2f variant.  This function should be called at least once
      before CmdAuthenticate or CmdRegister to make sure the object is using the
      proper transport for the device.
  
      Returns:
        The version of the U2F protocol in use.
      """
      self.logger.debug('CmdVersion')
      response = self.InternalSendApdu(apdu.CommandApdu(
          0, apdu.CMD_VERSION, 0x00, 0x00))
  
      if not response.IsSuccess():
        raise errors.ApduError(response.sw1, response.sw2)
  
      return response.body
  
    def CmdBlink(self, time):
      self.logger.debug('CmdBlink')
      self.transport.SendBlink(time)
  
    def CmdWink(self):
      self.logger.debug('CmdWink')
      self.transport.SendWink()
  
    def CmdPing(self, data):
      self.logger.debug('CmdPing')
      return self.transport.SendPing(data)
  
    def InternalSendApdu(self, apdu_to_send):
      """Send an APDU to the device.
  
      Sends an APDU to the device, possibly falling back to the legacy
      encoding format that is not ISO7816-4 compatible.
  
      Args:
        apdu_to_send: The CommandApdu object to send
  
      Returns:
        The ResponseApdu object constructed out of the devices reply.
      """
      response = None
      if not self.use_legacy_format:
        response = apdu.ResponseApdu(self.transport.SendMsgBytes(
            apdu_to_send.ToByteArray()))
        if response.sw1 == 0x67 and response.sw2 == 0x00:
          # If we failed using the standard format, retry with the
          # legacy format.
          self.use_legacy_format = True
          return self.InternalSendApdu(apdu_to_send)
      else:
        response = apdu.ResponseApdu(self.transport.SendMsgBytes(
            apdu_to_send.ToLegacyU2FByteArray()))
      return response
  