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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import absolute_import, division, print_function
import hmac
import os
from cryptography.hazmat.bindings.utils import LazyLibrary, build_ffi
with open(os.path.join(os.path.dirname(__file__), "src/constant_time.h")) as f:
TYPES = f.read()
with open(os.path.join(os.path.dirname(__file__), "src/constant_time.c")) as f:
FUNCTIONS = f.read()
_ffi = build_ffi(cdef_source=TYPES, verify_source=FUNCTIONS)
_lib = LazyLibrary(_ffi)
if hasattr(hmac, "compare_digest"):
def bytes_eq(a, b):
if not isinstance(a, bytes) or not isinstance(b, bytes):
raise TypeError("a and b must be bytes.")
return hmac.compare_digest(a, b)
else:
def bytes_eq(a, b):
if not isinstance(a, bytes) or not isinstance(b, bytes):
raise TypeError("a and b must be bytes.")
return _lib.Cryptography_constant_time_bytes_eq(
a, len(a), b, len(b)
) == 1
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