path: root/libavutil/aes_ctr.c (plain)
blob: e9c568fe0d13dd569ca151c29d7b97503cbd05ef

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