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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.
import abc
import typing
from cryptography import utils
from cryptography.exceptions import (
AlreadyFinalized,
AlreadyUpdated,
NotYetFinalized,
UnsupportedAlgorithm,
_Reasons,
)
from cryptography.hazmat.backends import _get_backend
from cryptography.hazmat.backends.interfaces import CipherBackend
from cryptography.hazmat.primitives._cipheralgorithm import CipherAlgorithm
from cryptography.hazmat.primitives.ciphers import modes
class BlockCipherAlgorithm(metaclass=abc.ABCMeta):
@abc.abstractproperty
def block_size(self) -> int:
"""
The size of a block as an integer in bits (e.g. 64, 128).
"""
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) -> 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(metaclass=abc.ABCMeta):
@abc.abstractmethod
def authenticate_additional_data(self, data: bytes) -> None:
"""
Authenticates the provided bytes.
"""
class AEADDecryptionContext(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(metaclass=abc.ABCMeta):
@abc.abstractproperty
def tag(self) -> bytes:
"""
Returns tag bytes. This is only available after encryption is
finalized.
"""
class Cipher(object):
def __init__(
self,
algorithm: CipherAlgorithm,
mode: typing.Optional[modes.Mode],
backend=None,
):
backend = _get_backend(backend)
if not isinstance(backend, CipherBackend):
raise UnsupportedAlgorithm(
"Backend object does not implement CipherBackend.",
_Reasons.BACKEND_MISSING_INTERFACE,
)
if not isinstance(algorithm, CipherAlgorithm):
raise TypeError("Expected interface of CipherAlgorithm.")
if mode is not None:
mode.validate_for_algorithm(algorithm)
self.algorithm = algorithm
self.mode = mode
self._backend = backend
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."
)
ctx = self._backend.create_symmetric_encryption_ctx(
self.algorithm, self.mode
)
return self._wrap_ctx(ctx, encrypt=True)
def decryptor(self):
ctx = self._backend.create_symmetric_decryption_ctx(
self.algorithm, self.mode
)
return self._wrap_ctx(ctx, encrypt=False)
def _wrap_ctx(self, ctx, encrypt):
if isinstance(self.mode, modes.ModeWithAuthenticationTag):
if encrypt:
return _AEADEncryptionContext(ctx)
else:
return _AEADCipherContext(ctx)
else:
return _CipherContext(ctx)
@utils.register_interface(CipherContext)
class _CipherContext(object):
def __init__(self, ctx):
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) -> 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
@utils.register_interface(AEADCipherContext)
@utils.register_interface(CipherContext)
@utils.register_interface(AEADDecryptionContext)
class _AEADCipherContext(object):
def __init__(self, ctx):
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):
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))
return self._ctx.update(data)
def update_into(self, data: bytes, buf) -> int:
self._check_limit(len(data))
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 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
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)
@utils.register_interface(AEADEncryptionContext)
class _AEADEncryptionContext(_AEADCipherContext):
@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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