Bitwise XOR operation between strings

Question

Level 1

2 points

Bitwise XOR operation between strings

Hi!! Here i come again...
The problem this time is with encoding datas using XOR operator.
My xml string is "NSMutableString xmlString" and my key string is a "char *key". Then, i need to operate the bitwise XOR between this two strings and than send the result to the server.
How can i implement this?
I think i've to convert the two strings in NSData then make the comparison with ^ operator...is that correct?
Thank you for help

MacBook Pro 2,4 Ghz 15,4", Mac OS X (10.5.3)

Posted on Sep 9, 2008 4:22 AM

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Answer 1

Sep 10, 2008 8:56 PM in response to McKracken

Not sure why you would ever need to do something like this oO
The result will probably be garbage, at least not human-readable...

But maybe you can try something along the lines of


NSString* string1;
NSString* string2;
NSString* result;
result = (*string1) | (*string2);

ugly and so on, but remember Objective C is still C!
Of course this bears all kinds of the usual risks when playng with pointers and memory...

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Answer 2

orangekay

Level 5

4,085 points

Sep 10, 2008 9:36 PM in response to Max Ullinger

That's not a XOR and all it's going to produce is an invalid pointer. If you want to operate on the string data itself then you have to do it manually, character by character.

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Answer 3

McKracken Author

Level 1

2 points

Sep 11, 2008 1:30 AM in response to McKracken

Then, i'll try to say a little more...

I've this:

NSString *myObjString = @"myString";
NSString *myObjkey = @"12345678";
char myObjresult;

then, i need to do the xor between myString and key: in C a can make this, having two char variables

char myCString;
char myCKey;
char myCResult;

myResult = char ( (int)myString ^ (int)myKey )

and it's ok in C. But in objective-c it doesn't run as I thought...i tried to make the casting on the NSString object, like this:

char myObjResult = char ( (int) myObjString ^ (int) myObjkey );

it rises no error, but i don't know how to transform myObjResult in a NSData and check it consistency. The only configuration that doesn't rise any error (but i think there's something wrong) is this:

Then, i'll try to say a little more...

I've this:

NSString *myObjString = @"myString";
NSString *myObjkey = @"12345678";
char myObjresult;

char myObjResult = char ( (int) myObjString ^ (int) myObjkey );

If I control the value of myObjResult with a NSLog("%c", myObjResult), i see a different value everytime i run my project...

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Answer 4

Arca

Level 1

60 points

Sep 11, 2008 8:57 AM in response to McKracken

What you need to do is xor the raw data either char by char, or by packing 4 chars into an int and xor-ing them:
char val, key, result[[47]];

val = [[objString charAtIndex:i]];
key = [[keyString charAtIndex:i]];
result[ ] = val ^ key;

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