program one_pad;
  uses dos;
  var infile, keyfile, outfile: file of byte;
      plain, key, cipher: byte;
begin
  if paramcount < 3 then
    begin
      writeln('Usage: one_pad infile keyfile outfile')
    end
  else
    begin
      assign(infile, paramstr(1));
      reset(infile);
      assign(keyfile, paramstr(2));
      reset(keyfile);
      assign(outfile, paramstr(3));
      rewrite(outfile);
      while (not eof(infile)) and (not eof(keyfile)) do
        begin
          read(infile, plain);
          read(keyfile, key);
    {The following single line does the encryption/decryption.}
          cipher := plain xor key;
          write(outfile, cipher);
        end;
      close(outfile);
      close(infile);
      close(keyfile);
    end
end.