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/*
* AES-CTR cipher
* Copyright (c) 2015 Eran Kornblau <erankor at gmail dot com>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "common.h"
#include "aes_ctr.h"
#include "aes.h"
#include "random_seed.h"
#define AES_BLOCK_SIZE (16)
typedef struct AVAESCTR {
struct AVAES* aes;
uint8_t counter[AES_BLOCK_SIZE];
uint8_t encrypted_counter[AES_BLOCK_SIZE];
int block_offset;
} AVAESCTR;
struct AVAESCTR *av_aes_ctr_alloc(void)
{
return av_mallocz(sizeof(struct AVAESCTR));
}
void av_aes_ctr_set_iv(struct AVAESCTR *a, const uint8_t* iv)
{
memcpy(a->counter, iv, AES_CTR_IV_SIZE);
memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
a->block_offset = 0;
}
const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
{
return a->counter;
}
void av_aes_ctr_set_random_iv(struct AVAESCTR *a)
{
uint32_t iv[2];
iv[0] = av_get_random_seed();
iv[1] = av_get_random_seed();
av_aes_ctr_set_iv(a, (uint8_t*)iv);
}
int av_aes_ctr_init(struct AVAESCTR *a, const uint8_t *key)
{
a->aes = av_aes_alloc();
if (!a->aes) {
return AVERROR(ENOMEM);
}
av_aes_init(a->aes, key, 128, 0);
memset(a->counter, 0, sizeof(a->counter));
a->block_offset = 0;
return 0;
}
void av_aes_ctr_free(struct AVAESCTR *a)
{
if (a) {
av_freep(&a->aes);
av_free(a);
}
}
static void av_aes_ctr_increment_be64(uint8_t* counter)
{
uint8_t* cur_pos;
for (cur_pos = counter + 7; cur_pos >= counter; cur_pos--) {
(*cur_pos)++;
if (*cur_pos != 0) {
break;
}
}
}
void av_aes_ctr_increment_iv(struct AVAESCTR *a)
{
av_aes_ctr_increment_be64(a->counter);
memset(a->counter + AES_CTR_IV_SIZE, 0, sizeof(a->counter) - AES_CTR_IV_SIZE);
a->block_offset = 0;
}
void av_aes_ctr_crypt(struct AVAESCTR *a, uint8_t *dst, const uint8_t *src, int count)
{
const uint8_t* src_end = src + count;
const uint8_t* cur_end_pos;
uint8_t* encrypted_counter_pos;
while (src < src_end) {
if (a->block_offset == 0) {
av_aes_crypt(a->aes, a->encrypted_counter, a->counter, 1, NULL, 0);
av_aes_ctr_increment_be64(a->counter + 8);
}
encrypted_counter_pos = a->encrypted_counter + a->block_offset;
cur_end_pos = src + AES_BLOCK_SIZE - a->block_offset;
cur_end_pos = FFMIN(cur_end_pos, src_end);
a->block_offset += cur_end_pos - src;
a->block_offset &= (AES_BLOCK_SIZE - 1);
while (src < cur_end_pos) {
*dst++ = *src++ ^ *encrypted_counter_pos++;
}
}
}
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