/*
  * RC4 encryption/decryption/pseudo-random number generator
  * Copyright (c) 2007 Reimar Doeffinger
  *

  * loosely based on LibTomCrypt by Tom St Denis
  *

  * 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 "avutil.h"

 #include "common.h"
 #include "rc4.h"
 

 typedef struct AVRC4 AVRC4;
 
 int av_rc4_init(AVRC4 *r, const uint8_t *key, int key_bits, int decrypt) {

     int i, j;

     uint8_t y;
     uint8_t *state = r->state;
     int keylen = key_bits >> 3;
     if (key_bits & 7)
         return -1;

     for (i = 0; i < 256; i++)
         state[i] = i;
     y = 0;
     // j is i % keylen
     for (j = 0, i = 0; i < 256; i++, j++) {
         if (j == keylen) j = 0;
         y += state[i] + key[j];
         FFSWAP(uint8_t, state[i], state[y]);
     }

     r->x = 1;
     r->y = state[1];
     return 0;
 }
 
 void av_rc4_crypt(AVRC4 *r, uint8_t *dst, const uint8_t *src, int count, uint8_t *iv, int decrypt) {
     uint8_t x = r->x, y = r->y;
     uint8_t *state = r->state;
     while (count-- > 0) {

         uint8_t sum = state[x] + state[y];
         FFSWAP(uint8_t, state[x], state[y]);

         *dst++ = src ? *src++ ^ state[sum] : state[sum];

         x++;
         y += state[x];
     }

     r->x = x; r->y = y;
 }