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  # Copyright (c) 2014, Legrandin <helderijs@gmail.com>
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  # ===================================================================
  
  """
  Counter with CBC-MAC (CCM) mode.
  """
  
  __all__ = ['CcmMode']
  
  from Crypto.Util.py3compat import byte_string, b, bchr, bord, unhexlify
  
  from Crypto.Util.strxor import strxor
  from Crypto.Util.number import long_to_bytes
  
  from Crypto.Hash import BLAKE2s
  from Crypto.Random import get_random_bytes
  
  
  def enum(**enums):
      return type('Enum', (), enums)
  
  MacStatus = enum(NOT_STARTED=0, PROCESSING_AUTH_DATA=1, PROCESSING_PLAINTEXT=2)
  
  
  class CcmMode(object):
      """Counter with CBC-MAC (CCM).
  
      This is an Authenticated Encryption with Associated Data (`AEAD`_) mode.
      It provides both confidentiality and authenticity.
  
      The header of the message may be left in the clear, if needed, and it will
      still be subject to authentication. The decryption step tells the receiver
      if the message comes from a source that really knowns the secret key.
      Additionally, decryption detects if any part of the message - including the
      header - has been modified or corrupted.
  
      This mode requires a nonce. The nonce shall never repeat for two
      different messages encrypted with the same key, but it does not need
      to be random.
      Note that there is a trade-off between the size of the nonce and the
      maximum size of a single message you can encrypt.
  
      It is important to use a large nonce if the key is reused across several
      messages and the nonce is chosen randomly.
  
      It is acceptable to us a short nonce if the key is only used a few times or
      if the nonce is taken from a counter.
  
      The following table shows the trade-off when the nonce is chosen at
      random. The column on the left shows how many messages it takes
      for the keystream to repeat **on average**. In practice, you will want to
      stop using the key way before that.
  
      +--------------------+---------------+-------------------+
      | Avg. # of messages |    nonce      |     Max. message  |
      | before keystream   |    size       |     size          |
      | repeats            |    (bytes)    |     (bytes)       |
      +====================+===============+===================+
      |       2^52         |      13       |        64K        |
      +--------------------+---------------+-------------------+
      |       2^48         |      12       |        16M        |
      +--------------------+---------------+-------------------+
      |       2^44         |      11       |         4G        |
      +--------------------+---------------+-------------------+
      |       2^40         |      10       |         1T        |
      +--------------------+---------------+-------------------+
      |       2^36         |       9       |        64P        |
      +--------------------+---------------+-------------------+
      |       2^32         |       8       |        16E        |
      +--------------------+---------------+-------------------+
  
      This mode is only available for ciphers that operate on 128 bits blocks
      (e.g. AES but not TDES).
  
      See `NIST SP800-38C`_ or RFC3610_.
  
      .. _`NIST SP800-38C`: http://csrc.nist.gov/publications/nistpubs/800-38C/SP800-38C.pdf
      .. _RFC3610: https://tools.ietf.org/html/rfc3610
      .. _AEAD: http://blog.cryptographyengineering.com/2012/05/how-to-choose-authenticated-encryption.html
  
      :undocumented: __init__
      """
  
      def __init__(self, factory, key, nonce, mac_len, msg_len, assoc_len,
                   cipher_params):
  
          self.block_size = factory.block_size
          """The block size of the underlying cipher, in bytes."""
  
          self.nonce = nonce
          """The nonce used for this cipher instance"""
  
          self._factory = factory
          self._key = key
          self._mac_len = mac_len
          self._msg_len = msg_len
          self._assoc_len = assoc_len
          self._cipher_params = cipher_params
  
          self._mac_tag = None  # Cache for MAC tag
  
          if self.block_size != 16:
              raise ValueError("CCM mode is only available for ciphers"
                               " that operate on 128 bits blocks")
  
          # MAC tag length (Tlen)
          if mac_len not in (4, 6, 8, 10, 12, 14, 16):
              raise ValueError("Parameter 'mac_len' must be even"
                               " and in the range 4..16 (not %d)" % mac_len)
  
          # Nonce value
          if not (nonce and 7 <= len(nonce) <= 13):
              raise ValueError("Length of parameter 'nonce' must be"
                               " in the range 7..13 bytes")
  
          # Create MAC object (the tag will be the last block
          # bytes worth of ciphertext)
          self._mac = self._factory.new(key,
                                        factory.MODE_CBC,
                                        iv=bchr(0) * 16,
                                        **cipher_params)
          self._mac_status = MacStatus.NOT_STARTED
          self._t = None
  
          # Allowed transitions after initialization
          self._next = [self.update, self.encrypt, self.decrypt,
                        self.digest, self.verify]
  
          # Cumulative lengths
          self._cumul_assoc_len = 0
          self._cumul_msg_len = 0
  
          # Cache for unaligned associated data/plaintext.
          # This is a list, but when the MAC starts, it will become a binary
          # string no longer than the block size.
          self._cache = []
  
          # Start CTR cipher, by formatting the counter (A.3)
          q = 15 - len(nonce)  # length of Q, the encoded message length
          self._cipher = self._factory.new(key,
                                           self._factory.MODE_CTR,
                                           nonce=bchr(q - 1) + nonce,
                                           **cipher_params)
  
          # S_0, step 6 in 6.1 for j=0
          self._s_0 = self._cipher.encrypt(bchr(0) * 16)
  
          # Try to start the MAC
          if None not in (assoc_len, msg_len):
              self._start_mac()
  
      def _start_mac(self):
  
          assert(self._mac_status == MacStatus.NOT_STARTED)
          assert(None not in (self._assoc_len, self._msg_len))
          assert(isinstance(self._cache, list))
  
          # Formatting control information and nonce (A.2.1)
          q = 15 - len(self.nonce)  # length of Q, the encoded message length
          flags = (64 * (self._assoc_len > 0) + 8 * ((self._mac_len - 2) // 2) +
                   (q - 1))
          b_0 = bchr(flags) + self.nonce + long_to_bytes(self._msg_len, q)
  
          # Formatting associated data (A.2.2)
          # Encoded 'a' is concatenated with the associated data 'A'
          assoc_len_encoded = b('')
          if self._assoc_len > 0:
              if self._assoc_len < (2 ** 16 - 2 ** 8):
                  enc_size = 2
              elif self._assoc_len < (2 ** 32):
                  assoc_len_encoded = b('\xFF\xFE')
                  enc_size = 4
              else:
                  assoc_len_encoded = b('\xFF\xFF')
                  enc_size = 8
              assoc_len_encoded += long_to_bytes(self._assoc_len, enc_size)
  
          # b_0 and assoc_len_encoded must be processed first
          self._cache.insert(0, b_0)
          self._cache.insert(1, assoc_len_encoded)
  
          # Process all the data cached so far
          first_data_to_mac = b("").join(self._cache)
          self._cache = b("")
          self._mac_status = MacStatus.PROCESSING_AUTH_DATA
          self._update(first_data_to_mac)
  
      def _pad_cache_and_update(self):
  
          assert(self._mac_status != MacStatus.NOT_STARTED)
          assert(byte_string(self._cache))
          assert(len(self._cache) < self.block_size)
  
          # Associated data is concatenated with the least number
          # of zero bytes (possibly none) to reach alignment to
          # the 16 byte boundary (A.2.3)
          len_cache = len(self._cache)
          if len_cache > 0:
              self._update(bchr(0) * (self.block_size - len_cache))
  
      def update(self, assoc_data):
          """Protect associated data
  
          If there is any associated data, the caller has to invoke
          this function one or more times, before using
          ``decrypt`` or ``encrypt``.
  
          By *associated data* it is meant any data (e.g. packet headers) that
          will not be encrypted and will be transmitted in the clear.
          However, the receiver is still able to detect any modification to it.
          In CCM, the *associated data* is also called
          *additional authenticated data* (AAD).
  
          If there is no associated data, this method must not be called.
  
          The caller may split associated data in segments of any size, and
          invoke this method multiple times, each time with the next segment.
  
          :Parameters:
            assoc_data : byte string
              A piece of associated data. There are no restrictions on its size.
          """
  
          if self.update not in self._next:
              raise TypeError("update() can only be called"
                              " immediately after initialization")
  
          self._next = [self.update, self.encrypt, self.decrypt,
                        self.digest, self.verify]
  
          self._cumul_assoc_len += len(assoc_data)
          if self._assoc_len is not None and \
             self._cumul_assoc_len > self._assoc_len:
              raise ValueError("Associated data is too long")
  
          self._update(assoc_data)
          return self
  
      def _update(self, assoc_data_pt=b("")):
          """Update the MAC with associated data or plaintext
             (without FSM checks)"""
  
          if self._mac_status == MacStatus.NOT_STARTED:
              self._cache.append(assoc_data_pt)
              return
  
          assert(byte_string(self._cache))
          assert(len(self._cache) < self.block_size)
  
          if len(self._cache) > 0:
              filler = min(self.block_size - len(self._cache),
                           len(assoc_data_pt))
              self._cache += assoc_data_pt[:filler]
              assoc_data_pt = assoc_data_pt[filler:]
  
              if len(self._cache) < self.block_size:
                  return
  
              # The cache is exactly one block
              self._t = self._mac.encrypt(self._cache)
              self._cache = b("")
  
          update_len = len(assoc_data_pt) // self.block_size * self.block_size
          self._cache = assoc_data_pt[update_len:]
          if update_len > 0:
              self._t = self._mac.encrypt(assoc_data_pt[:update_len])[-16:]
  
      def encrypt(self, plaintext):
          """Encrypt data with the key set at initialization.
  
          A cipher object is stateful: once you have encrypted a message
          you cannot encrypt (or decrypt) another message using the same
          object.
  
          This method can be called only **once** if ``msg_len`` was
          not passed at initialization.
  
          If ``msg_len`` was given, the data to encrypt can be broken
          up in two or more pieces and `encrypt` can be called
          multiple times.
  
          That is, the statement:
  
              >>> c.encrypt(a) + c.encrypt(b)
  
          is equivalent to:
  
               >>> c.encrypt(a+b)
  
          This function does not add any padding to the plaintext.
  
          :Parameters:
            plaintext : byte string
              The piece of data to encrypt.
              It can be of any length.
          :Return:
              the encrypted data, as a byte string.
              It is as long as *plaintext*.
          """
  
          if self.encrypt not in self._next:
              raise TypeError("encrypt() can only be called after"
                              " initialization or an update()")
          self._next = [self.encrypt, self.digest]
  
          # No more associated data allowed from now
          if self._assoc_len is None:
              assert(isinstance(self._cache, list))
              self._assoc_len = sum([len(x) for x in self._cache])
              if self._msg_len is not None:
                  self._start_mac()
          else:
              if self._cumul_assoc_len < self._assoc_len:
                  raise ValueError("Associated data is too short")
  
          # Only once piece of plaintext accepted if message length was
          # not declared in advance
          if self._msg_len is None:
              self._msg_len = len(plaintext)
              self._start_mac()
              self._next = [self.digest]
  
          self._cumul_msg_len += len(plaintext)
          if self._cumul_msg_len > self._msg_len:
              raise ValueError("Message is too long")
  
          if self._mac_status == MacStatus.PROCESSING_AUTH_DATA:
              # Associated data is concatenated with the least number
              # of zero bytes (possibly none) to reach alignment to
              # the 16 byte boundary (A.2.3)
              self._pad_cache_and_update()
              self._mac_status = MacStatus.PROCESSING_PLAINTEXT
  
          self._update(plaintext)
          return self._cipher.encrypt(plaintext)
  
      def decrypt(self, ciphertext):
          """Decrypt data with the key set at initialization.
  
          A cipher object is stateful: once you have decrypted a message
          you cannot decrypt (or encrypt) another message with the same
          object.
  
          This method can be called only **once** if ``msg_len`` was
          not passed at initialization.
  
          If ``msg_len`` was given, the data to decrypt can be
          broken up in two or more pieces and `decrypt` can be
          called multiple times.
  
          That is, the statement:
  
              >>> c.decrypt(a) + c.decrypt(b)
  
          is equivalent to:
  
               >>> c.decrypt(a+b)
  
          This function does not remove any padding from the plaintext.
  
          :Parameters:
            ciphertext : byte string
              The piece of data to decrypt.
              It can be of any length.
  
          :Return: the decrypted data (byte string).
          """
  
          if self.decrypt not in self._next:
              raise TypeError("decrypt() can only be called"
                              " after initialization or an update()")
          self._next = [self.decrypt, self.verify]
  
          # No more associated data allowed from now
          if self._assoc_len is None:
              assert(isinstance(self._cache, list))
              self._assoc_len = sum([len(x) for x in self._cache])
              if self._msg_len is not None:
                  self._start_mac()
          else:
              if self._cumul_assoc_len < self._assoc_len:
                  raise ValueError("Associated data is too short")
  
          # Only once piece of ciphertext accepted if message length was
          # not declared in advance
          if self._msg_len is None:
              self._msg_len = len(ciphertext)
              self._start_mac()
              self._next = [self.verify]
  
          self._cumul_msg_len += len(ciphertext)
          if self._cumul_msg_len > self._msg_len:
              raise ValueError("Message is too long")
  
          if self._mac_status == MacStatus.PROCESSING_AUTH_DATA:
              # Associated data is concatenated with the least number
              # of zero bytes (possibly none) to reach alignment to
              # the 16 byte boundary (A.2.3)
              self._pad_cache_and_update()
              self._mac_status = MacStatus.PROCESSING_PLAINTEXT
  
          # Encrypt is equivalent to decrypt with the CTR mode
          plaintext = self._cipher.encrypt(ciphertext)
          self._update(plaintext)
          return plaintext
  
      def digest(self):
          """Compute the *binary* MAC tag.
  
          The caller invokes this function at the very end.
  
          This method returns the MAC that shall be sent to the receiver,
          together with the ciphertext.
  
          :Return: the MAC, as a byte string.
          """
  
          if self.digest not in self._next:
              raise TypeError("digest() cannot be called when decrypting"
                              " or validating a message")
          self._next = [self.digest]
          return self._digest()
  
      def _digest(self):
          if self._mac_tag:
              return self._mac_tag
  
          if self._assoc_len is None:
              assert(isinstance(self._cache, list))
              self._assoc_len = sum([len(x) for x in self._cache])
              if self._msg_len is not None:
                  self._start_mac()
          else:
              if self._cumul_assoc_len < self._assoc_len:
                  raise ValueError("Associated data is too short")
  
          if self._msg_len is None:
              self._msg_len = 0
              self._start_mac()
  
          if self._cumul_msg_len != self._msg_len:
              raise ValueError("Message is too short")
  
          # Both associated data and payload are concatenated with the least
          # number of zero bytes (possibly none) that align it to the
          # 16 byte boundary (A.2.2 and A.2.3)
          self._pad_cache_and_update()
  
          # Step 8 in 6.1 (T xor MSB_Tlen(S_0))
          self._mac_tag = strxor(self._t, self._s_0)[:self._mac_len]
  
          return self._mac_tag
  
      def hexdigest(self):
          """Compute the *printable* MAC tag.
  
          This method is like `digest`.
  
          :Return: the MAC, as a hexadecimal string.
          """
          return "".join(["%02x" % bord(x) for x in self.digest()])
  
      def verify(self, received_mac_tag):
          """Validate the *binary* MAC tag.
  
          The caller invokes this function at the very end.
  
          This method checks if the decrypted message is indeed valid
          (that is, if the key is correct) and it has not been
          tampered with while in transit.
  
          :Parameters:
            received_mac_tag : byte string
              This is the *binary* MAC, as received from the sender.
          :Raises ValueError:
              if the MAC does not match. The message has been tampered with
              or the key is incorrect.
          """
  
          if self.verify not in self._next:
              raise TypeError("verify() cannot be called"
                              " when encrypting a message")
          self._next = [self.verify]
  
          self._digest()
          secret = get_random_bytes(16)
  
          mac1 = BLAKE2s.new(digest_bits=160, key=secret, data=self._mac_tag)
          mac2 = BLAKE2s.new(digest_bits=160, key=secret, data=received_mac_tag)
  
          if mac1.digest() != mac2.digest():
              raise ValueError("MAC check failed")
  
      def hexverify(self, hex_mac_tag):
          """Validate the *printable* MAC tag.
  
          This method is like `verify`.
  
          :Parameters:
            hex_mac_tag : string
              This is the *printable* MAC, as received from the sender.
          :Raises ValueError:
              if the MAC does not match. The message has been tampered with
              or the key is incorrect.
          """
  
          self.verify(unhexlify(hex_mac_tag))
  
      def encrypt_and_digest(self, plaintext):
          """Perform encrypt() and digest() in one step.
  
          :Parameters:
            plaintext : byte string
              The piece of data to encrypt.
          :Return:
              a tuple with two byte strings:
  
              - the encrypted data
              - the MAC
          """
  
          return self.encrypt(plaintext), self.digest()
  
      def decrypt_and_verify(self, ciphertext, received_mac_tag):
          """Perform decrypt() and verify() in one step.
  
          :Parameters:
            ciphertext : byte string
              The piece of data to decrypt.
            received_mac_tag : byte string
              This is the *binary* MAC, as received from the sender.
  
          :Return: the decrypted data (byte string).
          :Raises ValueError:
              if the MAC does not match. The message has been tampered with
              or the key is incorrect.
          """
  
          plaintext = self.decrypt(ciphertext)
          self.verify(received_mac_tag)
          return plaintext
  
  
  def _create_ccm_cipher(factory, **kwargs):
      """Create a new block cipher, configured in CCM mode.
  
      :Parameters:
        factory : module
          A symmetric cipher module from `Crypto.Cipher` (like
          `Crypto.Cipher.AES`).
  
      :Keywords:
        key : byte string
          The secret key to use in the symmetric cipher.
  
        nonce : byte string
          A value that must never be reused for any other encryption.
  
          Its length must be in the range ``[7..13]``.
          11 or 12 bytes are reasonable values in general. Bear in
          mind that with CCM there is a trade-off between nonce length and
          maximum message size.
  
          If not specified, a 11 byte long random string is used.
  
        mac_len : integer
          Length of the MAC, in bytes. It must be even and in
          the range ``[4..16]``. The default is 16.
  
        msg_len : integer
          Length of the message to (de)cipher.
          If not specified, ``encrypt`` or ``decrypt`` may only be called once.
  
        assoc_len : integer
          Length of the associated data.
          If not specified, all data is internally buffered.
      """
  
      try:
          key = key = kwargs.pop("key")
      except KeyError as e:
          raise TypeError("Missing parameter: " + str(e))
  
      nonce = kwargs.pop("nonce", None)  # N
      if nonce is None:
          nonce = get_random_bytes(11)
      mac_len = kwargs.pop("mac_len", factory.block_size)
      msg_len = kwargs.pop("msg_len", None)      # p
      assoc_len = kwargs.pop("assoc_len", None)  # a
      cipher_params = dict(kwargs)
  
      return CcmMode(factory, key, nonce, mac_len, msg_len,
                     assoc_len, cipher_params)
  