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