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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 typing
from cryptography.exceptions import InvalidTag, UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.primitives import ciphers
from cryptography.hazmat.primitives.ciphers import algorithms, modes
if typing.TYPE_CHECKING:
from cryptography.hazmat.backends.openssl.backend import Backend
class _CipherContext:
_ENCRYPT = 1
_DECRYPT = 0
_MAX_CHUNK_SIZE = 2**30 - 1
def __init__(self, backend: Backend, cipher, mode, operation: int) -> None:
self._backend = backend
self._cipher = cipher
self._mode = mode
self._operation = operation
self._tag: typing.Optional[bytes] = 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 = f"cipher {cipher.name} "
if mode is not None:
msg += f"in {mode.name} 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, algorithms.ChaCha20):
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,
)
# Check for XTS mode duplicate keys error
errors = self._backend._consume_errors()
lib = self._backend._lib
if res == 0 and (
(
not lib.CRYPTOGRAPHY_IS_LIBRESSL
and errors[0]._lib_reason_match(
lib.ERR_LIB_EVP, lib.EVP_R_XTS_DUPLICATED_KEYS
)
)
or (
lib.Cryptography_HAS_PROVIDERS
and errors[0]._lib_reason_match(
lib.ERR_LIB_PROV, lib.PROV_R_XTS_DUPLICATED_KEYS
)
)
):
raise ValueError("In XTS mode duplicated keys are not allowed")
self._backend.openssl_assert(res != 0, errors=errors)
# 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: bytes) -> bytes:
buf = bytearray(len(data) + self._block_size_bytes - 1)
n = self.update_into(data, buf)
return bytes(buf[:n])
def update_into(self, data: bytes, buf: bytes) -> int:
total_data_len = len(data)
if len(buf) < (total_data_len + self._block_size_bytes - 1):
raise ValueError(
"buffer must be at least {} bytes for this "
"payload".format(len(data) + self._block_size_bytes - 1)
)
data_processed = 0
total_out = 0
outlen = self._backend._ffi.new("int *")
baseoutbuf = self._backend._ffi.from_buffer(buf, require_writable=True)
baseinbuf = self._backend._ffi.from_buffer(data)
while data_processed != total_data_len:
outbuf = baseoutbuf + total_out
inbuf = baseinbuf + data_processed
inlen = min(self._MAX_CHUNK_SIZE, total_data_len - data_processed)
res = self._backend._lib.EVP_CipherUpdate(
self._ctx, outbuf, outlen, inbuf, inlen
)
if res == 0 and isinstance(self._mode, modes.XTS):
self._backend._consume_errors()
raise ValueError(
"In XTS mode you must supply at least a full block in the "
"first update call. For AES this is 16 bytes."
)
else:
self._backend.openssl_assert(res != 0)
data_processed += inlen
total_out += outlen[0]
return total_out
def finalize(self) -> bytes:
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
lib = self._backend._lib
self._backend.openssl_assert(
errors[0]._lib_reason_match(
lib.ERR_LIB_EVP,
lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH,
)
or (
lib.Cryptography_HAS_PROVIDERS
and errors[0]._lib_reason_match(
lib.ERR_LIB_PROV,
lib.PROV_R_WRONG_FINAL_BLOCK_LENGTH,
)
)
or (
lib.CRYPTOGRAPHY_IS_BORINGSSL
and errors[0].reason
== lib.CIPHER_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH
),
errors=errors,
)
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_reset(self._ctx)
self._backend.openssl_assert(res == 1)
return self._backend._ffi.buffer(buf)[: outlen[0]]
def finalize_with_tag(self, tag: bytes) -> bytes:
tag_len = len(tag)
if tag_len < self._mode._min_tag_length:
raise ValueError(
"Authentication tag must be {} bytes or longer.".format(
self._mode._min_tag_length
)
)
elif tag_len > self._block_size_bytes:
raise ValueError(
"Authentication tag cannot be more than {} bytes.".format(
self._block_size_bytes
)
)
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: bytes) -> None:
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)
@property
def tag(self) -> typing.Optional[bytes]:
return self._tag
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