1 /**
2 * \file ctr.h
3 *
4 * \brief This file contains common functionality for counter algorithms.
5 *
6 * Copyright The Mbed TLS Contributors
7 * SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
8 */
9
10 #ifndef MBEDTLS_CTR_H
11 #define MBEDTLS_CTR_H
12
13 #include "common.h"
14
15 /**
16 * \brief Increment a big-endian 16-byte value.
17 * This is quite performance-sensitive for AES-CTR and CTR-DRBG.
18 *
19 * \param n A 16-byte value to be incremented.
20 */
mbedtls_ctr_increment_counter(uint8_t n[16])21 static inline void mbedtls_ctr_increment_counter(uint8_t n[16])
22 {
23 // The 32-bit version seems to perform about the same as a 64-bit version
24 // on 64-bit architectures, so no need to define a 64-bit version.
25 for (int i = 3;; i--) {
26 uint32_t x = MBEDTLS_GET_UINT32_BE(n, i << 2);
27 x += 1;
28 MBEDTLS_PUT_UINT32_BE(x, n, i << 2);
29 if (x != 0 || i == 0) {
30 break;
31 }
32 }
33 }
34
35 #endif /* MBEDTLS_CTR_H */
36