1 /** 2 * Constant-time functions 3 */ 4 /* 5 * Copyright The Mbed TLS Contributors 6 * SPDX-License-Identifier: Apache-2.0 7 * 8 * Licensed under the Apache License, Version 2.0 (the "License"); you may 9 * not use this file except in compliance with the License. 10 * You may obtain a copy of the License at 11 * 12 * http://www.apache.org/licenses/LICENSE-2.0 13 * 14 * Unless required by applicable law or agreed to in writing, software 15 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 16 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 17 * See the License for the specific language governing permissions and 18 * limitations under the License. 19 */ 20 21 #ifndef MBEDTLS_CONSTANT_TIME_H 22 #define MBEDTLS_CONSTANT_TIME_H 23 24 #include <stddef.h> 25 26 27 /** Constant-time buffer comparison without branches. 28 * 29 * This is equivalent to the standard memcmp function, but is likely to be 30 * compiled to code using bitwise operation rather than a branch. 31 * 32 * This function can be used to write constant-time code by replacing branches 33 * with bit operations using masks. 34 * 35 * \param a Pointer to the first buffer. 36 * \param b Pointer to the second buffer. 37 * \param n The number of bytes to compare in the buffer. 38 * 39 * \return Zero if the content of the two buffer is the same, 40 * otherwise non-zero. 41 */ 42 int mbedtls_ct_memcmp(const void *a, 43 const void *b, 44 size_t n); 45 46 #endif /* MBEDTLS_CONSTANT_TIME_H */ 47