xref: /third_party/ffmpeg/libavutil/aes_ctr.c (revision cabdff1a) 
1/*
2 * AES-CTR cipher
3 * Copyright (c) 2015 Eran Kornblau <erankor at gmail dot com>
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22#include <string.h>
23
24#include "aes_ctr.h"
25#include "aes.h"
26#include "aes_internal.h"
27#include "macros.h"
28#include "mem.h"
29#include "random_seed.h"
30
31#define AES_BLOCK_SIZE (16)
32
33typedef struct AVAESCTR {
34    uint8_t counter[AES_BLOCK_SIZE];
35    uint8_t encrypted_counter[AES_BLOCK_SIZE];
36    int block_offset;
37    AVAES aes;
38} AVAESCTR;
39
40struct AVAESCTR *av_aes_ctr_alloc(void)
41{
42    return av_mallocz(sizeof(struct AVAESCTR));
43}
44
45void av_aes_ctr_set_iv(struct AVAESCTR *a, const uint8_t* iv)
46{
47    memcpy(a->counter, iv, AES_CTR_IV_SIZE);
48    memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
49    a->block_offset = 0;
50}
51
52void av_aes_ctr_set_full_iv(struct AVAESCTR *a, const uint8_t* iv)
53{
54    memcpy(a->counter, iv, sizeof(a->counter));
55    a->block_offset = 0;
56}
57
58const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
59{
60    return a->counter;
61}
62
63void av_aes_ctr_set_random_iv(struct AVAESCTR *a)
64{
65    uint32_t iv[2];
66
67    iv[0] = av_get_random_seed();
68    iv[1] = av_get_random_seed();
69
70    av_aes_ctr_set_iv(a, (uint8_t*)iv);
71}
72
73int av_aes_ctr_init(struct AVAESCTR *a, const uint8_t *key)
74{
75    av_aes_init(&a->aes, key, 128, 0);
76
77    memset(a->counter, 0, sizeof(a->counter));
78    a->block_offset = 0;
79
80    return 0;
81}
82
83void av_aes_ctr_free(struct AVAESCTR *a)
84{
85    av_free(a);
86}
87
88static void av_aes_ctr_increment_be64(uint8_t* counter)
89{
90    uint8_t* cur_pos;
91
92    for (cur_pos = counter + 7; cur_pos >= counter; cur_pos--) {
93        (*cur_pos)++;
94        if (*cur_pos != 0) {
95            break;
96        }
97    }
98}
99
100void av_aes_ctr_increment_iv(struct AVAESCTR *a)
101{
102    av_aes_ctr_increment_be64(a->counter);
103    memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
104    a->block_offset = 0;
105}
106
107void av_aes_ctr_crypt(struct AVAESCTR *a, uint8_t *dst, const uint8_t *src, int count)
108{
109    const uint8_t* src_end = src + count;
110    const uint8_t* cur_end_pos;
111    uint8_t* encrypted_counter_pos;
112
113    while (src < src_end) {
114        if (a->block_offset == 0) {
115            av_aes_crypt(&a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
116
117            av_aes_ctr_increment_be64(a->counter + 8);
118        }
119
120        encrypted_counter_pos = a->encrypted_counter + a->block_offset;
121        cur_end_pos = src + AES_BLOCK_SIZE - a->block_offset;
122        cur_end_pos = FFMIN(cur_end_pos, src_end);
123
124        a->block_offset += cur_end_pos - src;
125        a->block_offset &= (AES_BLOCK_SIZE - 1);
126
127        while (src < cur_end_pos) {
128            *dst++ = *src++ ^ *encrypted_counter_pos++;
129        }
130    }
131}
132