/*
  * 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++;
         }
     }
 }