Thread: Require help decrypting XOR.

Hello, all.

After what seems like hours of searching on various search engines, and websites, I have decided to come here for help.

I have this code:

Code:

for ( int i = 0; i < encrypt_input.length(); i++ ) {
	      encrypt_input[i] = encrypt_input[i]^key[i];
	      cout << encrypt_input[i];
	  }

Does anyone know how I would go about decrypting the encrypted result?

Thanks in advance.

Hi, and thanks for your reply.

Unfortunately I do not know if you're being sarcastic, or not, as I just started learning cryptography involving C++.

Would you mind further explaining?

The point of XOR is that it undoes itself (much like rot13); if you re-encrypt the encrypted thing you get the original back.

Originally Posted by tabstop

The point of XOR is that it undoes itself (much like rot13); if you re-encrypt the encrypted thing you get the original back.

That's funny, I've already tried that, although I will try something else, and get back to you.

After going over a few things, I am getting somewhat of the desired output, but not all of it, and one or two characters are capitalized, when they are supposed to be lowercase.

Are there any errors in the code snippet that anyone can point out?

It's basically like this:

Code:

	if ( option == crypter ) {
			cout << "\nEncrypt or decrypt? - ";
			cin >> crypter_option;
			if ( crypter_option == encrypt ) {
				system("cls");
				cout << "\nEnter text:\n";
				cin >> encrypt_input;
				//getline(cin, encrypt_input, '`');
				//reverse(encrypt_input.begin(), encrypt_input.end());
				system("cls");
				for ( int i = 0; i < encrypt_input.length(); i++ ) {
					encrypt_input[i] = encrypt_input[i]^key[i];
					cout << encrypt_input[i];
				}
				cout << "\n";
			}
......

Code:

string key = "ABCDEFGHIJK";

Originally Posted by mkthnx001

It's basically like this:

Code:

	if ( option == crypter ) {
			cout << "\nEncrypt or decrypt? - ";
			cin >> crypter_option;
			if ( crypter_option == encrypt ) {
				system("cls");
				cout << "\nEnter text:\n";
				cin >> encrypt_input;
				//getline(cin, encrypt_input, '`');
				//reverse(encrypt_input.begin(), encrypt_input.end());
				system("cls");
				for ( int i = 0; i < encrypt_input.length(); i++ ) {
					encrypt_input[i] = encrypt_input[i]^key[i];
					cout << encrypt_input[i];
				}
				cout << "\n";
			}
......

Code:

string key = "ABCDEFGHIJK";

Everything you've posted here works perfectly, assuming encrypt is defined appropriately and you type a string of 11 letters or less. You will probably want to make sure i doesn't walk off the end of key either (presumably you want to do i%11 or something).

Originally Posted by tabstop

Everything you've posted here works perfectly, assuming encrypt is defined appropriately and you type a string of 11 letters or less. You will probably want to make sure i doesn't walk off the end of key either (presumably you want to do i%11 or something).

Just to be clear, using getline(cin, encrypt_input, '`'); will cause errors, unlike cin >> encrypt_input;, right?

Originally Posted by matsp

Why? The only difference would be how it handles spaces and line ending - are you sure you want people to type in a back-quote to end the sentence? Seems a bit obscure, compared to the usual method of newline.

--
Mats

I was asking because I seemed to be getting the wrong output when decrypting, while using said code, but after replacing the back-quote character with the new line character, the problem seems to have been solved.

Although this brings upon another problem, how would I allow new lines (enter) being used in the input text, without it terminating? Would I have to use a different delimiter character? I don't want any common characters being able to terminate the input, is all.