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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)
@utils.register_interface(ciphers.AEADDecryptionContext)
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_bytes = self._cipher.block_size // 8
else:
self._block_size_bytes = 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 {} in {} 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:
msg = "cipher {0.name} ".format(cipher)
if mode is not None:
msg += "in {0.name} mode ".format(mode)
msg += (
"is not supported by this backend (Your version of OpenSSL "
"may be too old. Current version: {}.)"
).format(self._backend.openssl_version_text())
raise UnsupportedAlgorithm(msg, _Reasons.UNSUPPORTED_CIPHER)
if isinstance(mode, modes.ModeWithInitializationVector):
iv_nonce = self._backend._ffi.from_buffer(
mode.initialization_vector
)
elif isinstance(mode, modes.ModeWithTweak):
iv_nonce = self._backend._ffi.from_buffer(mode.tweak)
elif isinstance(mode, modes.ModeWithNonce):
iv_nonce = self._backend._ffi.from_buffer(mode.nonce)
elif isinstance(cipher, modes.ModeWithNonce):
iv_nonce = self._backend._ffi.from_buffer(cipher.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_AEAD_SET_IVLEN,
len(iv_nonce), self._backend._ffi.NULL
)
self._backend.openssl_assert(res != 0)
if mode.tag is not None:
res = self._backend._lib.EVP_CIPHER_CTX_ctrl(
ctx, self._backend._lib.EVP_CTRL_AEAD_SET_TAG,
len(mode.tag), mode.tag
)
self._backend.openssl_assert(res != 0)
self._tag = mode.tag
# pass key/iv
res = self._backend._lib.EVP_CipherInit_ex(
ctx,
self._backend._ffi.NULL,
self._backend._ffi.NULL,
self._backend._ffi.from_buffer(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):
buf = bytearray(len(data) + self._block_size_bytes - 1)
n = self.update_into(data, buf)
return bytes(buf[:n])
def update_into(self, data, buf):
if len(buf) < (len(data) + self._block_size_bytes - 1):
raise ValueError(
"buffer must be at least {} bytes for this "
"payload".format(len(data) + self._block_size_bytes - 1)
)
buf = self._backend._ffi.cast(
"unsigned char *", self._backend._ffi.from_buffer(buf)
)
outlen = self._backend._ffi.new("int *")
res = self._backend._lib.EVP_CipherUpdate(
self._ctx, buf, outlen,
self._backend._ffi.from_buffer(data), len(data)
)
self._backend.openssl_assert(res != 0)
return outlen[0]
def finalize(self):
if (
self._operation == self._DECRYPT and
isinstance(self._mode, modes.ModeWithAuthenticationTag) and
self.tag is None
):
raise ValueError(
"Authentication tag must be provided when decrypting."
)
buf = self._backend._ffi.new("unsigned char[]", self._block_size_bytes)
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]._lib_reason_match(
self._backend._lib.ERR_LIB_EVP,
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):
tag_buf = self._backend._ffi.new(
"unsigned char[]", self._block_size_bytes
)
res = self._backend._lib.EVP_CIPHER_CTX_ctrl(
self._ctx, self._backend._lib.EVP_CTRL_AEAD_GET_TAG,
self._block_size_bytes, tag_buf
)
self._backend.openssl_assert(res != 0)
self._tag = self._backend._ffi.buffer(tag_buf)[:]
res = self._backend._lib.EVP_CIPHER_CTX_cleanup(self._ctx)
self._backend.openssl_assert(res == 1)
return self._backend._ffi.buffer(buf)[:outlen[0]]
def finalize_with_tag(self, tag):
if len(tag) < self._mode._min_tag_length:
raise ValueError(
"Authentication tag must be {} bytes or longer.".format(
self._mode._min_tag_length)
)
res = self._backend._lib.EVP_CIPHER_CTX_ctrl(
self._ctx, self._backend._lib.EVP_CTRL_AEAD_SET_TAG,
len(tag), tag
)
self._backend.openssl_assert(res != 0)
self._tag = tag
return self.finalize()
def authenticate_additional_data(self, data):
outlen = self._backend._ffi.new("int *")
res = self._backend._lib.EVP_CipherUpdate(
self._ctx, self._backend._ffi.NULL, outlen,
self._backend._ffi.from_buffer(data), len(data)
)
self._backend.openssl_assert(res != 0)
tag = utils.read_only_property("_tag")
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