"encripting" by using ^

**Trauts** · 11-09-2004

here's my code.

Code:

char * Encrypt ( const char * string, const char * key )
{
	//char * newString = const_cast<char*>(string);
	std::string result = string;

	for (int i=0; i<strlen(string); i++)
	{
		int pos = i;
		while ( (pos+1) > strlen(key) )
			pos -= strlen(key);

		result[i] = string[i] ^ key[pos];
	}

	return const_cast<char*>(result.c_str());
}

int main()
{
	char * lala = "Hi. This is a test.";
	const char * key = "STEAM_0:0:4549308";
	char * result = NULL;

	result = Encrypt( lala, key );

	printf("%s \n%s\n%s", lala, key, result);
	//for (int i=0; i<strlen(result); i++)
	//	printf("%i", result[i]);
	//printf("\n");

	return 0;
}

It doesn't seem to be working... Any ideas?
It doesn't seem to do what its supposed to, I get almost all the same character as my answer.

What I want to do is 'encrypt' using the key, and loop the key so that it doesn't go out of range.

**quzah** · 11-09-2004

Why don't you just find the length of the key, and use:

Code:

foo = key[ pos % key_length ];

Quzah.

**bithub** · 11-09-2004

For one thing, your Encrypt() method is returning a pointer to a local array. It would be better to copy the result into a passed buffer.

**Trauts** · 11-09-2004

Quzah, thanks for the idea. didn't think of using modulus =)

Bithub, thanks for the headsup =)

Bet you its working inside the function =)

**Trauts** · 11-09-2004

OK, I'm stuck on getting it to store it properly.

How can I do this without strdup? If I just directly put it in the pointer, it doesn't work.

if it were a single character, you'd do something like
void Encrypt(char source, char & output);

But how do you do that with an array?

Code:

char * Encrypt ( const char * input, const char * key, char * output )
{
	std::string result	= "\0";
	int inputlength		= strlen(input);
	int keylength		= strlen(key);

	for (int i=0; i<inputlength; i++)
		result += input[i] ^ key[i % keylength];

	output = strdup(result.c_str());

	return output;
}

int main()
{
	char * lala = "Hi. This is a test.";
	const char * key = "STEAM_0:0:4549308";
	char * result = NULL;

	result = Encrypt( lala, key, result );

	printf("%s \n%s\n%s", lala, key, result);
	//for (int i=0; i<strlen(result); i++)
	//	printf("%i", result[i]);
	//printf("\n");

	free(result);

	return 0;
}

**bithub** · 11-10-2004

Code:

void Encrypt ( const char * input, const char * key, char * output )
{
	int inputlength		= strlen(input);
	int keylength		= strlen(key);

	for (int i=0; i<inputlength; i++)
		output[i] = input[i] ^ key[i % keylength];

}

One thing you may want to consider adding to the above code, is passing in the length of your output buffer. This way you can be sure you dont write past the end of it.

**Sang-drax** · 11-10-2004

No, in C++ you should return an std::string.

Code:

std::string Encrypt ( std::string str, const char * key )
{
    std::string result;
    //magic ...
    return result;
}

**Trauts** · 11-10-2004

Sang-drax: When I tried your way, it returns the adress of a local, so I get a fairly giberish answer.

I would prefer to do it bithub's way. (i don't want to use a std::string)

It works, except when I try to free my memory.

Code:

void Encrypt ( const char * input, const char * key, char * output ) 
{
	int inputlength		= strlen(input);
	int keylength		= strlen(key);

	for (int i=0; i<inputlength; i++)
		output[i] = input[i] ^ key[i % keylength];
	output[inputsize] = '\0'; // Do i need this?
}

int main()
{
	char * lala = "Hi. This is a test.";
	const char * key = "STEAM_0:0:4549308";
	char * result = new char[strlen(lala+1)];

	Encrypt( lala, key, result );

	printf("%s \n%s\n%s", lala, key, result);
	//for (int i=0; i<strlen(result); i++)
	//	printf("%i", result[i]);
	//printf("\n");

	delete [] result; // THIS CRASHES IT!!!

	return 0;
}

this is the error I get:

DAMAGE: after Normal block (#53) at 0x00320850

I'm using Visual C++ 2003

**Trauts** · 11-10-2004

found it.

i was shifting the start of the strlen to the right one, not adding one to it

***ClownPimp*** · 11-10-2004

>output[inputsize] = '\0'; // Do i need this?

Where does 'inputsize' come from? Im guessing in this line your writing past the end of the buffer allocated for output buffer, which would explain why 'delete [] result;' crashes your program.

edit: nevermind :P

**Trauts** · 11-10-2004

I'm still having issues (I've expanded it now).

I have a string, which looks like this:

13 8 4.586000 128465278 1248
0.900000 1.200000 1.500000
1.150000 1.300000 1.200000
0.500000 0.300000 1.100000 1.200000 1.500000

There are newlines at the end of each line.

When I run the encrypt function on it, it seems like it only runs off of the first line! It gets a drastically shorter result than what I put in. I checked, and the input variable is correct.

If I run encrypt again, and therefore remove the xoring effect, I get ONLY this:

13 8 4.586000 12

As you can see, it is cutting off almost everything!!!

I believe the problem lies with

Code:

key[i % keylength];

Because if I change that to a constant, it works fine. It seems that after i >= keylength, thats where it stops outputting a value

Here's my actual code. Keep in mind, the long string is read from a file, but identical valuewise.

Code:

char* Encrypt ( const char * input, const char * key, char * output ) 
{
	int inputlength		= strlen(input);
	int keylength		= strlen(key);
 
	for (int i=0; i<inputlength; i++)
		output[i] = input[i] ^ key[i % keylength];
	output[inputlength] = '\0';
 
	return output;
}
 
int main()
{
	const char * key = "STEAM_0:0:4549308";
	char str[] = "13 8 4.586000 128465278 1248\n0.900000 1.200000 1.500000\n1.150000 1.300000 1.200000\n0.500000 0.300000 1.100000 1.200000 1.500000\n";
	char buf[2048];
	printf(Encrypt(str, key, buf));
 
	return 0;
}

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