Thread: xor encryption and streams

I tried to write a simple XOR encryption program. But it's not working properly. For some files is the output file longer, for some other shorter then it should be. Here is my source code:

Code:

/*

   XOR encryption - simple encryption algorithm

   use: xorenc [key] filename

   It encrypts file 'filename'; output is in file with the same name, but
   extension is changed to .enc

*/

/*
   problems:
	 *** should I use delete or delete[] operator?
		 see ~Key()
	 *** how to know whether it's EOF or not using cin and <iostream.h>?
		 see main() : while loop
	 *** is it good to use variable definitions in loop?
		 see main() : while loop
*/

#include <fstream.h>
#include <iostream.h>
#include <string.h>
#include <stdio.h>

const int MAX_KEY_LENGTH = 16;

class Key {
private:
  char *key;
  int next;
  int length;

public:
  Key(void) {
	key = new char[MAX_KEY_LENGTH];
  }

  Key(const char *s) { init(s); }

  ~Key(void) { delete key; }

  void init(const char *s);
  char get_next_char(void);
};

void
Key::init(const char *s)
{
  length = strlen(s);

  if (length == 0) {
	cerr << "Key is too short" << endl;
  }
  else if (length > MAX_KEY_LENGTH) {
	length = MAX_KEY_LENGTH;
  }

  key = new char[length+1];
  strncpy(key, s, length);
  key[length] = 0;

  next = 0;
}

char
Key::get_next_char(void)
{
  if (next < length)
	return key[next++];

  // we should repeat the key from beginning
  next = 1;
  return key[0];
}

void
usage(const char *program)
{
  cout << endl << "Use " << program << " [key] filename" << endl << endl;
}

char *
get_only_file_name(char *s)
{
  int i = 0;

  while (s[i] != '\0' && s[i] != '.')
	i++;

  if (s[i] != '\0')
	s[i] = '\0';

  return s;
}

char *
prompt_for_key(void)
{
  char s[100];

  cout << "Enter key for encrypting: ";
  return fgets(s, 100, stdin); // using fgets doesn't seem good..
}


int
main(int argc, char *argv[])
{
  ifstream in;
  ofstream out;
  Key key;

  if (argc <= 1) {
	cout << "Too few arguments" << endl;
	usage(argv[0]);
	return 0;
  }
  else if (argc == 2) {
	in.open(argv[1]);
	out.open(strcat(get_only_file_name(argv[1]), ".enc"));

	key.init(prompt_for_key());
  }
  else if (argc >= 3) {
	in.open(argv[2]);
	out.open(strcat(get_only_file_name(argv[2]), ".enc"));

	// creates an instance of Key class an initialize it
	key.init(argv[1]);
  }

  if (!in)
	cerr << endl << "Input file does not exist!" << endl << endl;

  if (!out)
	cerr << endl << "Cannot open output file!" << endl << endl;

  int c;

  while (1) {
	in >> c;
	if (in.eof())
	  break;
	out.put(c ^ key.get_next_char());
  }

  in.close();
  out.close();
  return 0;
}

And another question is about streams. How should I test whether the file is on its end? And how about formatting the output? (in C we have %6.2f for example) Do you know about some tutorial or what, so I'd be able to read it?

Thanks a lot, Hammer! I have fixed my bugs(like follows down here) and it's working now excellent!

Code:

 else if (argc == 2) {
	in.open(argv[1], ios::binary);

	char *filename;
	filename = new char[strlen(argv[1]) + 5];
	strcpy(filename, argv[1]);
	strcat(get_only_file_name(filename), ".enc");
	out.open(filename, ios::binary);
	delete filename;

	key.init(prompt_for_key());
  }

I have one more question: should I use

Code:

delete filename;

or

Code:

delete[] filename

?