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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 annotations
import abc
from cryptography import utils
from cryptography.exceptions import UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.primitives._cipheralgorithm import (
BlockCipherAlgorithm,
CipherAlgorithm,
)
class Mode(metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def name(self) -> str:
"""
A string naming this mode (e.g. "ECB", "CBC").
"""
@abc.abstractmethod
def validate_for_algorithm(self, algorithm: CipherAlgorithm) -> None:
"""
Checks that all the necessary invariants of this (mode, algorithm)
combination are met.
"""
class ModeWithInitializationVector(Mode, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def initialization_vector(self) -> utils.Buffer:
"""
The value of the initialization vector for this mode as bytes.
"""
class ModeWithTweak(Mode, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def tweak(self) -> utils.Buffer:
"""
The value of the tweak for this mode as bytes.
"""
class ModeWithNonce(Mode, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def nonce(self) -> utils.Buffer:
"""
The value of the nonce for this mode as bytes.
"""
class ModeWithAuthenticationTag(Mode, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def tag(self) -> bytes | None:
"""
The value of the tag supplied to the constructor of this mode.
"""
def _check_aes_key_length(self: Mode, algorithm: CipherAlgorithm) -> None:
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: ModeWithInitializationVector, algorithm: BlockCipherAlgorithm
) -> None:
iv_len = len(self.initialization_vector)
if iv_len * 8 != algorithm.block_size:
raise ValueError(f"Invalid IV size ({iv_len}) for {self.name}.")
def _check_nonce_length(
nonce: utils.Buffer, name: str, algorithm: CipherAlgorithm
) -> None:
if not isinstance(algorithm, BlockCipherAlgorithm):
raise UnsupportedAlgorithm(
f"{name} requires a block cipher algorithm",
_Reasons.UNSUPPORTED_CIPHER,
)
if len(nonce) * 8 != algorithm.block_size:
raise ValueError(f"Invalid nonce size ({len(nonce)}) for {name}.")
def _check_iv_and_key_length(
self: ModeWithInitializationVector, algorithm: CipherAlgorithm
) -> None:
if not isinstance(algorithm, BlockCipherAlgorithm):
raise UnsupportedAlgorithm(
f"{self} requires a block cipher algorithm",
_Reasons.UNSUPPORTED_CIPHER,
)
_check_aes_key_length(self, algorithm)
_check_iv_length(self, algorithm)