| |
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|
|
| 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) |
|
|
