libavutil/aes_ctr.c

   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
  40 struct AVAESCTR *av_aes_ctr_alloc(void)
  41 {
  42     return av_mallocz(sizeof(struct AVAESCTR));
  43 }
  44
  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
  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
  58 const uint8_t* av_aes_ctr_get_iv(struct AVAESCTR *a)
  59 {
  60     return a->counter;
  61 }
  62
  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
  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
  83 void av_aes_ctr_free(struct AVAESCTR *a)
  84 {
  85     av_free(a);
  86 }
  87
  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
 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
 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 }