mbedtls/library/constant_time.c

2  *  Constant-time functions
5  *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
101     /* We don't support int smaller than 32-bits, but if someone tried to build  in mbedtls_ct_memcmp()
103      * only bits set in diff are in the top 16-bits, and would be lost by a  in mbedtls_ct_memcmp()
106 #error "mbedtls_ct_memcmp() requires minimum 32-bit ints"  in mbedtls_ct_memcmp()
108     /* The bit-twiddling ensures that when we cast uint32_t to int, we are casting  in mbedtls_ct_memcmp()
109      * a value that is in the range 0..INT_MAX - a value larger than this would  in mbedtls_ct_memcmp()
112      * This ensures that the value returned by the function is non-zero iff  in mbedtls_ct_memcmp()
113      * diff is non-zero.  in mbedtls_ct_memcmp()
115     return (int) ((diff & 0xffff) | (diff >> 16));  in mbedtls_ct_memcmp()
132     size_t valid_end = n - skip_tail;  in mbedtls_ct_memcmp_partial()
142     /* Since we go byte-by-byte, the only bits set will be in the bottom 8 bits, so the  in mbedtls_ct_memcmp_partial()
155         mbedtls_ct_condition_t no_op = mbedtls_ct_uint_gt(total - offset, i);  in mbedtls_ct_memmove_left()
156         /* The first `total - offset` passes are a no-op. The last  in mbedtls_ct_memmove_left()
159         for (size_t n = 0; n < total - 1; n++) {  in mbedtls_ct_memmove_left()
164         buf[total-1] = mbedtls_ct_uint_if_else_0(no_op, buf[total-1]);  in mbedtls_ct_memmove_left()
187      * no-op because we read from dest and write the same data back into dest.  in mbedtls_ct_memcpy_if()
193     /* dest[i] = c1 == c2 ? src[i] : dest[i] */  in mbedtls_ct_memcpy_if()