void arcfour(unsigned char data[16], unsigned char data_out[16], unsigned char data_in[16])
{
  unsigned char s_box[256];
  unsigned char index_i = 0;
  unsigned char index_j = 0;
  unsigned char j = 0;
  int ind;

  for (ind = 0; ind != 255; ind++)
  {
    s_box[ind] = (unsigned char)ind;
  }

  for( ind = 0; ind < 256; ind++)
  {
     unsigned char tc;

     j += (s_box[ind] + data[ind%16]);

     tc = s_box[ind];
     s_box[ind] = s_box[j];
     s_box[j] = tc;
  }

  for( ind = 0; ind < 16; ind++)
  {
    unsigned char tc;
    unsigned char t;

    index_i++;
    index_j += s_box[index_i];

    tc = s_box[index_i];
    s_box[index_i] = s_box[index_j];
    s_box[index_j] = tc;

    t = s_box[index_i] + s_box[index_j];
    data_out[ind] = data_in[ind] ^ s_box[t];
  }
}