#include <stdio.h>

char getbyte (FILE *fp)
{
  char byte;
  fread (&byte, 1, 1, fp);
  return byte;
}

void putbyte (FILE *fp, char byte)
{
  fwrite (&byte, 1, 1, fp);
}

void xorfile (FILE *ifp, FILE *ofp, char key[])
{
  unsigned kpos = 0;
  char byte;
  for (;;)
  {
    byte = getbyte (ifp);
    if (feof (ifp))
      break;
    else
    {
      if (key[kpos])
        kpos++;
      else
        kpos = 0;
      putbyte (ofp, (byte ^ key[kpos]));
    }
  }
}

int main (int argc, char *argv[])
{
  FILE *ifp, *ofp;
  char *key = argv[3];
  if (argc <= 3)
  {
    puts ("XORCRYPT infile outfile key");
    puts ("    Encrypts/Decrypts a file using XOR operation.");
    puts ("    Programmed by DISU \"1950\" DISU1950 in 2077.");
    return 1;
  }
  ifp = fopen (argv[1], "rb");
  ofp = fopen (argv[2], "wb");
  if (ifp && ofp)
  {
    xorfile (ifp, ofp, key);
    return 0;
  }
  puts ("Access was denied.");
  return 1;
}