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# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
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"""
EAX mode.
"""

__all__ = ['EaxMode']

import struct
from binascii import unhexlify

from Crypto.Util.py3compat import byte_string, bord, _copy_bytes

from Crypto.Util._raw_api import is_buffer

from Crypto.Util.strxor import strxor
from Crypto.Util.number import long_to_bytes, bytes_to_long

from Crypto.Hash import CMAC, BLAKE2s
from Crypto.Random import get_random_bytes


class EaxMode(object):
    """*EAX* mode.

    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*.

    This mode is only available for ciphers that operate on 64 or
    128 bits blocks.

    There are no official standards defining EAX.
    The implementation is based on `a proposal`__ that
    was presented to NIST.

    .. _AEAD: http://blog.cryptographyengineering.com/2012/05/how-to-choose-authenticated-encryption.html
    .. __: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/eax/eax-spec.pdf

    :undocumented: __init__
    """

    def __init__(self, factory, key, nonce, mac_len, cipher_params):
        """EAX cipher mode"""

        self.block_size = factory.block_size
        """The block size of the underlying cipher, in bytes."""

        self.nonce = _copy_bytes(None, None, nonce)
        """The nonce originally used to create the object."""

        self._mac_len = mac_len
        self._mac_tag = None  # Cache for MAC tag

        # Allowed transitions after initialization
        self._next = ["update", "encrypt", "decrypt",
                      "digest", "verify"]

        # MAC tag length
        if not (2 <= self._mac_len <= self.block_size):
            raise ValueError("'mac_len' must be at least 2 and not larger than %d"
                             % self.block_size)

        # Nonce cannot be empty and must be a byte string
        if len(self.nonce) == 0:
            raise ValueError("Nonce cannot be empty in EAX mode")
        if not is_buffer(nonce):
            raise TypeError("nonce must be bytes, bytearray or memoryview")

        self._omac = [
                CMAC.new(key,