Thread: One of those nasty file read/write issues

So, I've been working on this object-oriented xor file encryptor of mine (Yeah, I know, what's the point), and I've come to an almost-done roadblock. It seems that for text and bitmap files my algorith functions correctly. However, ecrypting and then decrypting a wav file yields a "wrong format" erro when I try to play it in winamp. Obviously, I messed up some bits. Unfortunately, I don't know which bits or why. I've included excerpts from functions that encode and decode files. Yes, I'm using ios::binary.

Encoding:

Code:

//The actual encoding (writing)
 
 unsigned long int counter = 0;
 writer.open(encoded_path.c_str(),ios::binary);
 if(!writer) return CRYPT_FAIL;
 
 writer.write("XOR_CODEC_ENCRYPTED_FILE@",25); //write branding
 writer.write(orig_name.c_str(),orig_name.size());//write original file name
 writer.put('@');//separation character
 for(int y = 0; y < password.size(); y++) writer.put( (password[y] ^ PASSWORD_KEY) );
 writer.put('@'); //separation character
 writer.write(key.c_str(),key.size()); //write key
 writer.put('@'); //separation character
 
 char in_byte = '\0';
 cout << "Encrypting..." << endl;
 while( !((reader.get(in_byte)).eof()) )     // while get() does not set eof bit (get() into in_byte)
 {
  //ok, so this reads through input (with get) and writes char by char (using put)
  //    the xor-ed data. Modulus is used so counter can increase
  //    to whatever, while for key[index], index { [0,255]
  //    Thus, the key is effectively cycled through continuously
  writer.put( static_cast<char>(in_byte ^ key[counter % KEY_SIZE]) );
  counter++;
 }
 cout << "Encryption complete." << endl;
 reader.clear();//eof
 reader.seekg(0,ios::beg);//rewind
 //Note: as currently written, the encoder has a 4,294,967,295 byte limit ( max_val(unsigned long int) )
 encoded = true;

Now, when the decoder is called, the seek pointer on the encoded file is already past my little header, so (theoretically) only the original contents of the file are written):

Code:

 unsigned long int counter = 0;
 char in_byte = '\0';
 cout << "Decrypting..." << endl;
 while( !((reader.get(in_byte)).eof()) )     // while get() does not set eof bit (get() into in_byte)
 {
  //ok, so this reads through input (with get) and writes char by char (using put)
  //    the un-xor-ed data. Modulus is used so counter can increase
  //    to whatever, while for key[index], index { [0,255]
  //    Thus, the key is effectively cycled through continuously
  writer.put( static_cast<char>(in_byte ^ key[counter % KEY_SIZE]) );
  counter++;
 }
 cout << "Decryption complete." << endl;
 reader.clear();//eof
 reader.seekg(0,ios::beg);//rewind

PS: I apologize in advance for using eof() a loop conditional, but I don't think that's the problem (correct me if I'm wrong).

1. Are the input and output files the same size?

2. Prepare a 256 byte file with each byte set to 00, 01, 02 ... FF
- then encrypt it and decrypt it back to another file.
- then compare one set of 256 bytes with another set of 256 bytes.

have you tried the fc to understand which and how many bytes are broken?

I will certainly try Salem's idea. What do you mean, vart? fc?

>for(int y = 0; y < password.size(); y++) writer.put( (password[y] ^ PASSWORD_KEY) );
Did you try decrypting the password, and see what it prints?

fc is the command line compare tool

fc /b oldfile newfile
Will tell you the positions where corresponding bytes in two files differ.