1 /**
2  *  Constant-time functions
3  *
4  *  Copyright The Mbed TLS Contributors
5  *  SPDX-License-Identifier: Apache-2.0
6  *
7  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
8  *  not use this file except in compliance with the License.
9  *  You may obtain a copy of the License at
10  *
11  *  http://www.apache.org/licenses/LICENSE-2.0
12  *
13  *  Unless required by applicable law or agreed to in writing, software
14  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
15  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16  *  See the License for the specific language governing permissions and
17  *  limitations under the License.
18  */
19 
20 #ifndef MBEDTLS_CONSTANT_TIME_H
21 #define MBEDTLS_CONSTANT_TIME_H
22 
23 #include <stddef.h>
24 
25 
26 /** Constant-time buffer comparison without branches.
27  *
28  * This is equivalent to the standard memcmp function, but is likely to be
29  * compiled to code using bitwise operation rather than a branch.
30  *
31  * This function can be used to write constant-time code by replacing branches
32  * with bit operations using masks.
33  *
34  * \param a     Pointer to the first buffer.
35  * \param b     Pointer to the second buffer.
36  * \param n     The number of bytes to compare in the buffer.
37  *
38  * \return      Zero if the content of the two buffer is the same,
39  *              otherwise non-zero.
40  */
41 int mbedtls_ct_memcmp( const void *a,
42                        const void *b,
43                        size_t n );
44 
45 #endif /* MBEDTLS_CONSTANT_TIME_H */
46