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# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
from __future__ import absolute_import, division, print_function
import abc
import six
from cryptography import utils
@six.add_metaclass(abc.ABCMeta)
class Mode(object):
@abc.abstractproperty
def name(self):
"""
A string naming this mode (e.g. "ECB", "CBC").
"""
@abc.abstractmethod
def validate_for_algorithm(self, algorithm):
"""
Checks that all the necessary invariants of this (mode, algorithm)
combination are met.
"""
@six.add_metaclass(abc.ABCMeta)
class ModeWithInitializationVector(object):
@abc.abstractproperty
def initialization_vector(self):
"""
The value of the initialization vector for this mode as bytes.
"""
@six.add_metaclass(abc.ABCMeta)
class ModeWithTweak(object):
@abc.abstractproperty
def tweak(self):
"""
The value of the tweak for this mode as bytes.
"""
@six.add_metaclass(abc.ABCMeta)
class ModeWithNonce(object):
@abc.abstractproperty
def nonce(self):
"""
The value of the nonce for this mode as bytes.
"""
@six.add_metaclass(abc.ABCMeta)
class ModeWithAuthenticationTag(object):
@abc.abstractproperty
def tag(self):
"""
The value of the tag supplied to the constructor of this mode.
"""
def _check_aes_key_length(self, algorithm):
if algorithm.key_size > 256 and algorithm.name == "AES":
raise ValueError(
"Only 128, 192, and 256 bit keys are allowed for this AES mode"
)
def _check_iv_length(self, algorithm):
if len(self.initialization_vector) * 8 != algorithm.block_size:
raise ValueError(
"Invalid IV size ({}) for {}.".format(
len(self.initialization_vector), self.name
)
)
def _check_iv_and_key_length(self, algorithm):
_check_aes_key_length(self, algorithm)
_check_iv_length(self, algorithm)
@utils.register_interface(Mode)
@utils.register_interface(ModeWithInitializationVector)
class CBC(object):
name = "CBC"
def __init__(self, initialization_vector):
utils._check_byteslike("initialization_vector", initialization_vector)
self._initialization_vector = initialization_vector
initialization_vector = utils.read_only_property("_initialization_vector")
validate_for_algorithm = _check_iv_and_key_length
@utils.register_interface(Mode)
@utils.register_interface(ModeWithTweak)
class XTS(object):
name = "XTS"
def __init__(self, tweak):
utils._check_byteslike("tweak", tweak)
if len(tweak) != 16:
raise ValueError("tweak must be 128-bits (16 bytes)")
self._tweak = tweak
tweak = utils.read_only_property("_tweak")
def validate_for_algorithm(self, algorithm):
if algorithm.key_size not in (256, 512):
raise ValueError(
"The XTS specification requires a 256-bit key for AES-128-XTS"
" and 512-bit key for AES-256-XTS"
)
@utils.register_interface(Mode)
class ECB(object):
name = "ECB"
validate_for_algorithm = _check_aes_key_length
@utils.register_interface(Mode)
@utils.register_interface(ModeWithInitializationVector)
class OFB(object):
name = "OFB"
def __init__(self, initialization_vector):
utils._check_byteslike("initialization_vector", initialization_vector)
self._initialization_vector = initialization_vector
initialization_vector = utils.read_only_property("_initialization_vector")
validate_for_algorithm = _check_iv_and_key_length
@utils.register_interface(Mode)
@utils.register_interface(ModeWithInitializationVector)
class CFB(object):
name = "CFB"
def __init__(self, initialization_vector):
utils._check_byteslike("initialization_vector", initialization_vector)
self._initialization_vector = initialization_vector
initialization_vector = utils.read_only_property("_initialization_vector")
validate_for_algorithm = _check_iv_and_key_length
@utils.register_interface(Mode)
@utils.register_interface(ModeWithInitializationVector)
class CFB8(object):
name = "CFB8"
def __init__(self, initialization_vector):
utils._check_byteslike("initialization_vector", initialization_vector)
self._initialization_vector = initialization_vector
initialization_vector = utils.read_only_property("_initialization_vector")
validate_for_algorithm = _check_iv_and_key_length
@utils.register_interface(Mode)
@utils.register_interface(ModeWithNonce)
class CTR(object):
name = "CTR"
def __init__(self, nonce):
utils._check_byteslike("nonce", nonce)
self._nonce = nonce
nonce = utils.read_only_property("_nonce")
def validate_for_algorithm(self, algorithm):
_check_aes_key_length(self, algorithm)
if len(self.nonce) * 8 != algorithm.block_size:
raise ValueError(
"Invalid nonce size ({}) for {}.".format(
len(self.nonce), self.name
)
)
@utils.register_interface(Mode)
@utils.register_interface(ModeWithInitializationVector)
@utils.register_interface(ModeWithAuthenticationTag)
class GCM(object):
name = "GCM"
_MAX_ENCRYPTED_BYTES = (2 ** 39 - 256) // 8
_MAX_AAD_BYTES = (2 ** 64) // 8
def __init__(self, initialization_vector, tag=None, min_tag_length=16):
# len(initialization_vector) must in [1, 2 ** 64), but it's impossible
# to actually construct a bytes object that large, so we don't check
# for it
utils._check_byteslike("initialization_vector", initialization_vector)
if len(initialization_vector) == 0:
raise ValueError("initialization_vector must be at least 1 byte")
self._initialization_vector = initialization_vector
if tag is not None:
utils._check_bytes("tag", tag)
if min_tag_length < 4:
raise ValueError("min_tag_length must be >= 4")
if len(tag) < min_tag_length:
raise ValueError(
"Authentication tag must be {} bytes or longer.".format(
min_tag_length
)
)
self._tag = tag
self._min_tag_length = min_tag_length
tag = utils.read_only_property("_tag")
initialization_vector = utils.read_only_property("_initialization_vector")
def validate_for_algorithm(self, algorithm):
_check_aes_key_length(self, algorithm)
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