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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 absolute_import, division, print_function
from cryptography import utils
from cryptography.exceptions import InvalidTag, UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.primitives import ciphers
from cryptography.hazmat.primitives.ciphers import modes
@utils.register_interface(ciphers.CipherContext)
@utils.register_interface(ciphers.AEADCipherContext)
@utils.register_interface(ciphers.AEADEncryptionContext)
class _CipherContext(object):
_ENCRYPT = 1
_DECRYPT = 0
def __init__(self, backend, cipher, mode, operation):
self._backend = backend
self._cipher = cipher
self._mode = mode
self._operation = operation
self._tag = None
if isinstance(self._cipher, ciphers.BlockCipherAlgorithm):
self._block_size = self._cipher.block_size
else:
self._block_size = 1
ctx = self._backend._lib.EVP_CIPHER_CTX_new()
ctx = self._backend._ffi.gc(
ctx, self._backend._lib.EVP_CIPHER_CTX_free
)
registry = self._backend._cipher_registry
try:
adapter = registry[type(cipher), type(mode)]
except KeyError:
raise UnsupportedAlgorithm(
"cipher {0} in {1} mode is not supported "
"by this backend.".format(
cipher.name, mode.name if mode else mode),
_Reasons.UNSUPPORTED_CIPHER
)
evp_cipher = adapter(self._backend, cipher, mode)
if evp_cipher == self._backend._ffi.NULL:
raise UnsupportedAlgorithm(
"cipher {0} in {1} mode is not supported "
"by this backend.".format(
cipher.name, mode.name if mode else mode),
_Reasons.UNSUPPORTED_CIPHER
)
if isinstance(mode, modes.ModeWithInitializationVector):
iv_nonce = mode.initialization_vector
elif isinstance(mode, modes.ModeWithNonce):
iv_nonce = mode.nonce
else:
iv_nonce = self._backend._ffi.NULL
# begin init with cipher and operation type
res = self._backend._lib.EVP_CipherInit_ex(ctx, evp_cipher,
self._backend._ffi.NULL,
self._backend._ffi.NULL,
self._backend._ffi.NULL,
operation)
self._backend.openssl_assert(res != 0)
# set the key length to handle variable key ciphers
res = self._backend._lib.EVP_CIPHER_CTX_set_key_length(
ctx, len(cipher.key)
)
self._backend.openssl_assert(res != 0)
if isinstance(mode, modes.GCM):
res = self._backend._lib.EVP_CIPHER_CTX_ctrl(
ctx, self._backend._lib.EVP_CTRL_GCM_SET_IVLEN,
len(iv_nonce), self._backend._ffi.NULL
)
self._backend.openssl_assert(res != 0)
if operation == self._DECRYPT:
res = self._backend._lib.EVP_CIPHER_CTX_ctrl(
ctx, self._backend._lib.EVP_CTRL_GCM_SET_TAG,
len(mode.tag), mode.tag
)
self._backend.openssl_assert(res != 0)
# pass key/iv
res = self._backend._lib.EVP_CipherInit_ex(
ctx,
self._backend._ffi.NULL,
self._backend._ffi.NULL,
cipher.key,
iv_nonce,
operation
)
self._backend.openssl_assert(res != 0)
# We purposely disable padding here as it's handled higher up in the
# API.
self._backend._lib.EVP_CIPHER_CTX_set_padding(ctx, 0)
self._ctx = ctx
def update(self, data):
# OpenSSL 0.9.8e has an assertion in its EVP code that causes it
# to SIGABRT if you call update with an empty byte string. This can be
# removed when we drop support for 0.9.8e (CentOS/RHEL 5). This branch
# should be taken only when length is zero and mode is not GCM because
# AES GCM can return improper tag values if you don't call update
# with empty plaintext when authenticating AAD for ...reasons.
if len(data) == 0 and not isinstance(self._mode, modes.GCM):
return b""
buf = self._backend._ffi.new("unsigned char[]",
len(data) + self._block_size - 1)
outlen = self._backend._ffi.new("int *")
res = self._backend._lib.EVP_CipherUpdate(self._ctx, buf, outlen, data,
len(data))
self._backend.openssl_assert(res != 0)
return self._backend._ffi.buffer(buf)[:outlen[0]]
def finalize(self):
# OpenSSL 1.0.1 on Ubuntu 12.04 (and possibly other distributions)
# appears to have a bug where you must make at least one call to update
# even if you are only using authenticate_additional_data or the
# GCM tag will be wrong. An (empty) call to update resolves this
# and is harmless for all other versions of OpenSSL.
if isinstance(self._mode, modes.GCM):
self.update(b"")
buf = self._backend._ffi.new("unsigned char[]", self._block_size)
outlen = self._backend._ffi.new("int *")
res = self._backend._lib.EVP_CipherFinal_ex(self._ctx, buf, outlen)
if res == 0:
errors = self._backend._consume_errors()
if not errors and isinstance(self._mode, modes.GCM):
raise InvalidTag
self._backend.openssl_assert(
errors[0][1:] == (
self._backend._lib.ERR_LIB_EVP,
self._backend._lib.EVP_F_EVP_ENCRYPTFINAL_EX,
self._backend._lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH
) or errors[0][1:] == (
self._backend._lib.ERR_LIB_EVP,
self._backend._lib.EVP_F_EVP_DECRYPTFINAL_EX,
self._backend._lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH
)
)
raise ValueError(
"The length of the provided data is not a multiple of "
"the block length."
)
if (isinstance(self._mode, modes.GCM) and
self._operation == self._ENCRYPT):
block_byte_size = self._block_size // 8
tag_buf = self._backend._ffi.new(
"unsigned char[]", block_byte_size
)
res = self._backend._lib.EVP_CIPHER_CTX_ctrl(
self._ctx, self._backend._lib.EVP_CTRL_GCM_GET_TAG,
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