1 /** 2 * Constant-time functions 3 */ 4 /* 5 * Copyright The Mbed TLS Contributors 6 * SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later 7 */ 8 9 #ifndef MBEDTLS_CONSTANT_TIME_H 10 #define MBEDTLS_CONSTANT_TIME_H 11 12 #include <stddef.h> 13 14 /** Constant-time buffer comparison without branches. 15 * 16 * This is equivalent to the standard memcmp function, but is likely to be 17 * compiled to code using bitwise operations rather than a branch, such that 18 * the time taken is constant w.r.t. the data pointed to by \p a and \p b, 19 * and w.r.t. whether \p a and \p b are equal or not. It is not constant-time 20 * w.r.t. \p n . 21 * 22 * This function can be used to write constant-time code by replacing branches 23 * with bit operations using masks. 24 * 25 * \param a Pointer to the first buffer, containing at least \p n bytes. May not be NULL. 26 * \param b Pointer to the second buffer, containing at least \p n bytes. May not be NULL. 27 * \param n The number of bytes to compare. 28 * 29 * \return Zero if the contents of the two buffers are the same, 30 * otherwise non-zero. 31 */ 32 int mbedtls_ct_memcmp(const void *a, 33 const void *b, 34 size_t n); 35 36 #endif /* MBEDTLS_CONSTANT_TIME_H */ 37
