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 "common.h"
23 #include "aes_ctr.h"
24 #include "aes.h"
25 #include "random_seed.h"
26
27 #define AES_BLOCK_SIZE (16)
28
29 typedef struct AVAESCTR {
30 struct AVAES* aes;
31 uint8_t counter[AES_BLOCK_SIZE];
32 uint8_t encrypted_counter[AES_BLOCK_SIZE];
33 int block_offset;
34 } AVAESCTR;
35
av_aes_ctr_alloc(void)36 struct AVAESCTR *av_aes_ctr_alloc(void)
37 {
38 return av_mallocz(sizeof(struct AVAESCTR));
39 }
40
av_aes_ctr_set_iv(struct AVAESCTR * a,const uint8_t * iv)41 void av_aes_ctr_set_iv(struct AVAESCTR *a, const uint8_t* iv)
42 {
43 memcpy(a->counter, iv, AES_CTR_IV_SIZE);
44 memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
45 a->block_offset = 0;
46 }
47
av_aes_ctr_set_full_iv(struct AVAESCTR * a,const uint8_t * iv)48 void av_aes_ctr_set_full_iv(struct AVAESCTR *a, const uint8_t* iv)
49 {
50 memcpy(a->counter, iv, sizeof(a->counter));
51 a->block_offset = 0;
52 }
53
av_aes_ctr_get_iv(struct AVAESCTR * a)54 const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
55 {
56 return a->counter;
57 }
58
av_aes_ctr_set_random_iv(struct AVAESCTR * a)59 void av_aes_ctr_set_random_iv(struct AVAESCTR *a)
60 {
61 uint32_t iv[2];
62
63 iv[0] = av_get_random_seed();
64 iv[1] = av_get_random_seed();
65
66 av_aes_ctr_set_iv(a, (uint8_t*)iv);
67 }
68
av_aes_ctr_init(struct AVAESCTR * a,const uint8_t * key)69 int av_aes_ctr_init(struct AVAESCTR *a, const uint8_t *key)
70 {
71 a->aes = av_aes_alloc();
72 if (!a->aes) {
73 return AVERROR(ENOMEM);
74 }
75
76 av_aes_init(a->aes, key, 128, 0);
77
78 memset(a->counter, 0, sizeof(a->counter));
79 a->block_offset = 0;
80
81 return 0;
82 }
83
av_aes_ctr_free(struct AVAESCTR * a)84 void av_aes_ctr_free(struct AVAESCTR *a)
85 {
86 if (a) {
87 av_freep(&a->aes);
88 av_free(a);
89 }
90 }
91
av_aes_ctr_increment_be64(uint8_t * counter)92 static void av_aes_ctr_increment_be64(uint8_t* counter)
93 {
94 uint8_t* cur_pos;
95
96 for (cur_pos = counter + 7; cur_pos >= counter; cur_pos--) {
97 (*cur_pos)++;
98 if (*cur_pos != 0) {
99 break;
100 }
101 }
102 }
103
av_aes_ctr_increment_iv(struct AVAESCTR * a)104 void av_aes_ctr_increment_iv(struct AVAESCTR *a)
105 {
106 av_aes_ctr_increment_be64(a->counter);
107 memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
108 a->block_offset = 0;
109 }
110
av_aes_ctr_crypt(struct AVAESCTR * a,uint8_t * dst,const uint8_t * src,int count)111 void av_aes_ctr_crypt(struct AVAESCTR *a, uint8_t *dst, const uint8_t *src, int count)
112 {
113 const uint8_t* src_end = src + count;
114 const uint8_t* cur_end_pos;
115 uint8_t* encrypted_counter_pos;
116
117 while (src < src_end) {
118 if (a->block_offset == 0) {
119 av_aes_crypt(a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
120
121 av_aes_ctr_increment_be64(a->counter + 8);
122 }
123
124 encrypted_counter_pos = a->encrypted_counter + a->block_offset;
125 cur_end_pos = src + AES_BLOCK_SIZE - a->block_offset;
126 cur_end_pos = FFMIN(cur_end_pos, src_end);
127
128 a->block_offset += cur_end_pos - src;
129 a->block_offset &= (AES_BLOCK_SIZE - 1);
130
131 while (src < cur_end_pos) {
132 *dst++ = *src++ ^ *encrypted_counter_pos++;
133 }
134 }
135 }
136