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✏️ Editing: modes.py

# 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,
)
from cryptography.hazmat.primitives.ciphers import algorithms

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)

class CBC(ModeWithInitializationVector):
    name = "CBC"

def __init__(self, initialization_vector: utils.Buffer):
        utils._check_byteslike("initialization_vector", initialization_vector)
        self._initialization_vector = initialization_vector

@property
    def initialization_vector(self) -> utils.Buffer:
        return self._initialization_vector

validate_for_algorithm = _check_iv_and_key_length

class XTS(ModeWithTweak):
    name = "XTS"

def __init__(self, tweak: utils.Buffer):
        utils._check_byteslike("tweak", tweak)

if len(tweak) != 16:
            raise ValueError("tweak must be 128-bits (16 bytes)")

self._tweak = tweak

@property
    def tweak(self) -> utils.Buffer:
        return self._tweak

def validate_for_algorithm(self, algorithm: CipherAlgorithm) -> None:
        if isinstance(algorithm, (algorithms.AES128, algorithms.AES256)):
            raise TypeError(
                "The AES128 and AES256 classes do not support XTS, please use "
                "the standard AES class instead."
            )

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"
            )

class ECB(Mode):
    name = "ECB"

validate_for_algorithm = _check_aes_key_length

class OFB(ModeWithInitializationVector):
    name = "OFB"

def __init__(self, initialization_vector: utils.Buffer):
        utils._check_byteslike("initialization_vector", initialization_vector)
        self._initialization_vector = initialization_vector

@property
    def initialization_vector(self) -> utils.Buffer:
        return self._initialization_vector

validate_for_algorithm = _check_iv_and_key_length

class CFB(ModeWithInitializationVector):
    name = "CFB"

def __init__(self, initialization_vector: utils.Buffer):
        utils._check_byteslike("initialization_vector", initialization_vector)
        self._initialization_vector = initialization_vector

@property
    def initialization_vector(self) -> utils.Buffer:
        return self._initialization_vector

validate_for_algorithm = _check_iv_and_key_length

class CFB8(ModeWithInitializationVector):
    name = "CFB8"

def __init__(self, initialization_vector: utils.Buffer):
        utils._check_byteslike("initialization_vector", initialization_vector)
        self._initialization_vector = initialization_vector

@property
    def initialization_vector(self) -> utils.Buffer:
        return self._initialization_vector

validate_for_algorithm = _check_iv_and_key_length

class CTR(ModeWithNonce):
    name = "CTR"

def __init__(self, nonce: utils.Buffer):
        utils._check_byteslike("nonce", nonce)
        self._nonce = nonce

@property
    def nonce(self) -> utils.Buffer:
        return self._nonce

def validate_for_algorithm(self, algorithm: CipherAlgorithm) -> None:
        _check_aes_key_length(self, algorithm)
        _check_nonce_length(self.nonce, self.name, algorithm)

class GCM(ModeWithInitializationVector, ModeWithAuthenticationTag):
    name = "GCM"
    _MAX_ENCRYPTED_BYTES = (2**39 - 256) // 8
    _MAX_AAD_BYTES = (2**64) // 8

def __init__(
        self,
        initialization_vector: utils.Buffer,
        tag: bytes | None = None,
        min_tag_length: int = 16,
    ):
        # OpenSSL 3.0.0 constrains GCM IVs to [64, 1024] bits inclusive
        # This is a sane limit anyway so we'll enforce it here.
        utils._check_byteslike("initialization_vector", initialization_vector)
        if len(initialization_vector) < 8 or len(initialization_vector) > 128:
            raise ValueError(
                "initialization_vector must be between 8 and 128 bytes (64 "
                "and 1024 bits)."
            )
        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(
                    f"Authentication tag must be {min_tag_length} bytes or "
                    "longer."
                )
        self._tag = tag
        self._min_tag_length = min_tag_length

@property
    def tag(self) -> bytes | None:
        return self._tag

@property
    def initialization_vector(self) -> utils.Buffer:
        return self._initialization_vector

def validate_for_algorithm(self, algorithm: CipherAlgorithm) -> None:
        _check_aes_key_length(self, algorithm)
        if not isinstance(algorithm, BlockCipherAlgorithm):
            raise UnsupportedAlgorithm(
                "GCM requires a block cipher algorithm",
                _Reasons.UNSUPPORTED_CIPHER,
            )
        block_size_bytes = algorithm.block_size // 8
        if self._tag is not None and len(self._tag) > block_size_bytes:
            raise ValueError(
                f"Authentication tag cannot be more than {block_size_bytes} "
                "bytes."
            )

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