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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 typing
from cryptography.exceptions import (
InvalidSignature,
UnsupportedAlgorithm,
_Reasons,
)
from cryptography.hazmat.primitives import constant_time
from cryptography.hazmat.primitives.ciphers.modes import CBC
if typing.TYPE_CHECKING:
from cryptography.hazmat.primitives import ciphers
from cryptography.hazmat.backends.openssl.backend import Backend
class _CMACContext:
def __init__(
self,
backend: "Backend",
algorithm: "ciphers.BlockCipherAlgorithm",
ctx=None,
) -> None:
if not backend.cmac_algorithm_supported(algorithm):
raise UnsupportedAlgorithm(
"This backend does not support CMAC.",
_Reasons.UNSUPPORTED_CIPHER,
)
self._backend = backend
self._key = algorithm.key
self._algorithm = algorithm
self._output_length = algorithm.block_size // 8
if ctx is None:
registry = self._backend._cipher_registry
adapter = registry[type(algorithm), CBC]
evp_cipher = adapter(self._backend, algorithm, CBC)
ctx = self._backend._lib.CMAC_CTX_new()
self._backend.openssl_assert(ctx != self._backend._ffi.NULL)
ctx = self._backend._ffi.gc(ctx, self._backend._lib.CMAC_CTX_free)
key_ptr = self._backend._ffi.from_buffer(self._key)
res = self._backend._lib.CMAC_Init(
ctx,
key_ptr,
len(self._key),
evp_cipher,
self._backend._ffi.NULL,
)
self._backend.openssl_assert(res == 1)
self._ctx = ctx
def update(self, data: bytes) -> None:
res = self._backend._lib.CMAC_Update(self._ctx, data, len(data))
self._backend.openssl_assert(res == 1)
def finalize(self) -> bytes:
buf = self._backend._ffi.new("unsigned char[]", self._output_length)
length = self._backend._ffi.new("size_t *", self._output_length)
res = self._backend._lib.CMAC_Final(self._ctx, buf, length)
self._backend.openssl_assert(res == 1)
self._ctx = None
return self._backend._ffi.buffer(buf)[:]
def copy(self) -> "_CMACContext":
copied_ctx = self._backend._lib.CMAC_CTX_new()
copied_ctx = self._backend._ffi.gc(
copied_ctx, self._backend._lib.CMAC_CTX_free
)
res = self._backend._lib.CMAC_CTX_copy(copied_ctx, self._ctx)
self._backend.openssl_assert(res == 1)
return _CMACContext(self._backend, self._algorithm, ctx=copied_ctx)
def verify(self, signature: bytes) -> None:
digest = self.finalize()
if not constant_time.bytes_eq(digest, signature):
raise InvalidSignature("Signature did not match digest.")