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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
import typing
from cryptography.exceptions import (
AlreadyFinalized,
AlreadyUpdated,
NotYetFinalized,
)
from cryptography.hazmat.primitives._cipheralgorithm import CipherAlgorithm
from cryptography.hazmat.primitives.ciphers import modes
if typing.TYPE_CHECKING:
from cryptography.hazmat.backends.openssl.ciphers import (
_CipherContext as _BackendCipherContext,
)
class CipherContext(metaclass=abc.ABCMeta):
@abc.abstractmethod
def update(self, data: bytes) -> bytes:
"""
Processes the provided bytes through the cipher and returns the results
as bytes.
"""
@abc.abstractmethod
def update_into(self, data: bytes, buf: bytes) -> int:
"""
Processes the provided bytes and writes the resulting data into the
provided buffer. Returns the number of bytes written.
"""
@abc.abstractmethod
def finalize(self) -> bytes:
"""
Returns the results of processing the final block as bytes.
"""
class AEADCipherContext(CipherContext, metaclass=abc.ABCMeta):
@abc.abstractmethod
def authenticate_additional_data(self, data: bytes) -> None:
"""
Authenticates the provided bytes.
"""
class AEADDecryptionContext(AEADCipherContext, metaclass=abc.ABCMeta):
@abc.abstractmethod
def finalize_with_tag(self, tag: bytes) -> bytes:
"""
Returns the results of processing the final block as bytes and allows
delayed passing of the authentication tag.
"""
class AEADEncryptionContext(AEADCipherContext, metaclass=abc.ABCMeta):
@property
@abc.abstractmethod
def tag(self) -> bytes:
"""
Returns tag bytes. This is only available after encryption is
finalized.
"""
Mode = typing.TypeVar(
"Mode", bound=typing.Optional[modes.Mode], covariant=True
)
class Cipher(typing.Generic[Mode]):
def __init__(
self,
algorithm: CipherAlgorithm,
mode: Mode,
backend: typing.Any = None,
) -> None:
if not isinstance(algorithm, CipherAlgorithm):
raise TypeError("Expected interface of CipherAlgorithm.")
if mode is not None:
# mypy needs this assert to narrow the type from our generic
# type. Maybe it won't some time in the future.
assert isinstance(mode, modes.Mode)
mode.validate_for_algorithm(algorithm)
self.algorithm = algorithm
self.mode = mode
@typing.overload
def encryptor(
self: Cipher[modes.ModeWithAuthenticationTag],
) -> AEADEncryptionContext:
...
@typing.overload
def encryptor(
self: _CIPHER_TYPE,
) -> CipherContext:
...
def encryptor(self):
if isinstance(self.mode, modes.ModeWithAuthenticationTag):
if self.mode.tag is not None:
raise ValueError(
"Authentication tag must be None when encrypting."
)
from cryptography.hazmat.backends.openssl.backend import backend
ctx = backend.create_symmetric_encryption_ctx(
self.algorithm, self.mode
)
return self._wrap_ctx(ctx, encrypt=True)
@typing.overload
def decryptor(
self: Cipher[modes.ModeWithAuthenticationTag],
) -> AEADDecryptionContext:
...
@typing.overload
def decryptor(
self: _CIPHER_TYPE,
) -> CipherContext:
...
def decryptor(self):
from cryptography.hazmat.backends.openssl.backend import backend
ctx = backend.create_symmetric_decryption_ctx(
self.algorithm, self.mode
)
return self._wrap_ctx(ctx, encrypt=False)
def _wrap_ctx(
self, ctx: _BackendCipherContext, encrypt: bool
) -> typing.Union[
AEADEncryptionContext, AEADDecryptionContext, CipherContext
]:
if isinstance(self.mode, modes.ModeWithAuthenticationTag):
if encrypt:
return _AEADEncryptionContext(ctx)
else:
return _AEADDecryptionContext(ctx)
else:
return _CipherContext(ctx)
_CIPHER_TYPE = Cipher[
typing.Union[
modes.ModeWithNonce,
modes.ModeWithTweak,
None,
modes.ECB,
modes.ModeWithInitializationVector,
]
]
class _CipherContext(CipherContext):
_ctx: typing.Optional[_BackendCipherContext]
def __init__(self, ctx: _BackendCipherContext) -> None:
self._ctx = ctx
def update(self, data: bytes) -> bytes:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
return self._ctx.update(data)
def update_into(self, data: bytes, buf: bytes) -> int:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
return self._ctx.update_into(data, buf)
def finalize(self) -> bytes:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
data = self._ctx.finalize()
self._ctx = None
return data
class _AEADCipherContext(AEADCipherContext):
_ctx: typing.Optional[_BackendCipherContext]
_tag: typing.Optional[bytes]
def __init__(self, ctx: _BackendCipherContext) -> None:
self._ctx = ctx
self._bytes_processed = 0
self._aad_bytes_processed = 0
self._tag = None
self._updated = False
def _check_limit(self, data_size: int) -> None:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
self._updated = True
self._bytes_processed += data_size
if self._bytes_processed > self._ctx._mode._MAX_ENCRYPTED_BYTES:
raise ValueError(
"{} has a maximum encrypted byte limit of {}".format(
self._ctx._mode.name, self._ctx._mode._MAX_ENCRYPTED_BYTES
)
)
def update(self, data: bytes) -> bytes:
self._check_limit(len(data))
# mypy needs this assert even though _check_limit already checked
assert self._ctx is not None
return self._ctx.update(data)
def update_into(self, data: bytes, buf: bytes) -> int:
self._check_limit(len(data))
# mypy needs this assert even though _check_limit already checked
assert self._ctx is not None
return self._ctx.update_into(data, buf)
def finalize(self) -> bytes:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
data = self._ctx.finalize()
self._tag = self._ctx.tag
self._ctx = None
return data
def authenticate_additional_data(self, data: bytes) -> None:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
if self._updated:
raise AlreadyUpdated("Update has been called on this context.")
self._aad_bytes_processed += len(data)
if self._aad_bytes_processed > self._ctx._mode._MAX_AAD_BYTES:
raise ValueError(
"{} has a maximum AAD byte limit of {}".format(
self._ctx._mode.name, self._ctx._mode._MAX_AAD_BYTES
)
)
self._ctx.authenticate_additional_data(data)
class _AEADDecryptionContext(_AEADCipherContext, AEADDecryptionContext):
def finalize_with_tag(self, tag: bytes) -> bytes:
if self._ctx is None:
raise AlreadyFinalized("Context was already finalized.")
data = self._ctx.finalize_with_tag(tag)
self._tag = self._ctx.tag
self._ctx = None
return data
class _AEADEncryptionContext(_AEADCipherContext, AEADEncryptionContext):
@property
def tag(self) -> bytes:
if self._ctx is not None:
raise NotYetFinalized(
"You must finalize encryption before " "getting the tag."
)
assert self._tag is not None
return self._tag
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