src/cryptography/hazmat/primitives/constant_time.py

# 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

import hmac
import warnings

from cryptography import utils
from cryptography.hazmat.bindings._constant_time import lib


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:
    warnings.warn(
        "Support for your Python version is deprecated. The next version of "
        "cryptography will remove support. Please upgrade to a 2.7.x "
        "release that supports hmac.compare_digest as soon as possible.",
        utils.DeprecatedIn23,
    )

    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