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
33 typedef 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
av_aes_ctr_alloc(void)40 struct AVAESCTR *av_aes_ctr_alloc(void)
41 {
42 return av_mallocz(sizeof(struct AVAESCTR));
43 }
44
av_aes_ctr_set_iv(struct AVAESCTR * a,const uint8_t * iv)45 void 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
av_aes_ctr_set_full_iv(struct AVAESCTR * a,const uint8_t * iv)52 void 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
av_aes_ctr_get_iv(struct AVAESCTR * a)58 const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
59 {
60 return a->counter;
61 }
62
av_aes_ctr_set_random_iv(struct AVAESCTR * a)63 void 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
av_aes_ctr_init(struct AVAESCTR * a,const uint8_t * key)73 int 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
av_aes_ctr_free(struct AVAESCTR * a)83 void av_aes_ctr_free(struct AVAESCTR *a)
84 {
85 av_free(a);
86 }
87
av_aes_ctr_increment_be64(uint8_t * counter)88 static 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
av_aes_ctr_increment_iv(struct AVAESCTR * a)100 void 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
av_aes_ctr_crypt(struct AVAESCTR * a,uint8_t * dst,const uint8_t * src,int count)107 void 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