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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 sys
import cffi
import six
from cryptography.hazmat.bindings.utils import _create_modulename
TYPES = """
uint8_t Cryptography_constant_time_bytes_eq(uint8_t *, size_t, uint8_t *,
size_t);
"""
FUNCTIONS = """
uint8_t Cryptography_constant_time_bytes_eq(uint8_t *a, size_t len_a,
uint8_t *b, size_t len_b) {
size_t i = 0;
uint8_t mismatch = 0;
if (len_a != len_b) {
return 0;
}
for (i = 0; i < len_a; i++) {
mismatch |= a[i] ^ b[i];
}
/* Make sure any bits set are copied to the lowest bit */
mismatch |= mismatch >> 4;
mismatch |= mismatch >> 2;
mismatch |= mismatch >> 1;
/* Now check the low bit to see if it's set */
return (mismatch & 1) == 0;
}
"""
_ffi = cffi.FFI()
_ffi.cdef(TYPES)
_lib = _ffi.verify(
source=FUNCTIONS,
modulename=_create_modulename([TYPES], FUNCTIONS, sys.version),
ext_package="cryptography",
)
def bytes_eq(a, b):
if (not isinstance(a, six.binary_type) or
not isinstance(b, six.binary_type)):
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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