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# Copyright (c) 2021, Legrandin <helderijs@gmail.com>
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from binascii import unhexlify
from Crypto.Util.py3compat import bord, tobytes, is_bytes
from Crypto.Random import get_random_bytes
from . import cSHAKE128, SHA3_256
from .cSHAKE128 import _bytepad, _encode_str, _right_encode
class KMAC_Hash(object):
"""A KMAC hash object.
Do not instantiate directly.
Use the :func:`new` function.
"""
def __init__(self, data, key, mac_len, custom,
oid_variant, cshake, rate):
# See https://tools.ietf.org/html/rfc8702
self.oid = "2.16.840.1.101.3.4.2." + oid_variant
self.digest_size = mac_len
self._mac = None
partial_newX = _bytepad(_encode_str(tobytes(key)), rate)
self._cshake = cshake._new(partial_newX, custom, b"KMAC")
if data:
self._cshake.update(data)
def update(self, data):
"""Authenticate the next chunk of message.
Args:
data (bytes/bytearray/memoryview): The next chunk of the message to
authenticate.
"""
if self._mac:
raise TypeError("You can only call 'digest' or 'hexdigest' on this object")
self._cshake.update(data)
return self
def digest(self):
"""Return the **binary** (non-printable) MAC tag of the message.
:return: The MAC tag. Binary form.
:rtype: byte string
"""
if not self._mac:
self._cshake.update(_right_encode(self.digest_size * 8))
self._mac = self._cshake.read(self.digest_size)
return self._mac
def hexdigest(self):
"""Return the **printable** MAC tag of the message.
:return: The MAC tag. Hexadecimal encoded.
:rtype: string
"""
return "".join(["%02x" % bord(x) for x in tuple(self.digest())])
def verify(self, mac_tag):
"""Verify that a given **binary** MAC (computed by another party)
is valid.
Args:
mac_tag (bytes/bytearray/memoryview): the expected MAC of the message.
Raises:
ValueError: if the MAC does not match. It means that the message
has been tampered with or that the MAC key is incorrect.
"""
secret = get_random_bytes(16)
mac1 = SHA3_256.new(secret + mac_tag)
mac2 = SHA3_256.new(secret + self.digest())
if mac1.digest() != mac2.digest():
raise ValueError("MAC check failed")
def hexverify(self, hex_mac_tag):
"""Verify that a given **printable** MAC (computed by another party)
is valid.
Args:
hex_mac_tag (string): the expected MAC of the message, as a hexadecimal string.
Raises:
ValueError: if the MAC does not match. It means that the message
has been tampered with or that the MAC key is incorrect.
"""
self.verify(unhexlify(tobytes(hex_mac_tag)))
def new(self, **kwargs):
"""Return a new instance of a KMAC hash object.
See :func:`new`.
"""
if "mac_len" not in kwargs:
kwargs["mac_len"] = self.digest_size
return new(**kwargs)
def new(**kwargs):
"""Create a new KMAC128 object.
Args:
key (bytes/bytearray/memoryview):
The key to use to compute the MAC.
It must be at least 128 bits long (16 bytes).
data (bytes/bytearray/memoryview):
Optional. The very first chunk of the message to authenticate.
It is equivalent to an early call to :meth:`KMAC_Hash.update`.
mac_len (integer):
Optional. The size of the authentication tag, in bytes.
Default is 64. Minimum is 8.
custom (bytes/bytearray/memoryview):
Optional. A customization byte string (``S`` in SP 800-185).
Returns:
A :class:`KMAC_Hash` hash object
"""
key = kwargs.pop("key", None)
if not is_bytes(key):
raise TypeError("You must pass a key to KMAC128")
if len(key) < 16:
raise ValueError("The key must be at least 128 bits long (16 bytes)")
data = kwargs.pop("data", None)
mac_len = kwargs.pop("mac_len", 64)
if mac_len < 8:
raise ValueError("'mac_len' must be 8 bytes or more")
custom = kwargs.pop("custom", b"")
if kwargs:
raise TypeError("Unknown parameters: " + str(kwargs))
return KMAC_Hash(data, key, mac_len, custom, "19", cSHAKE128, 168)
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