Question

I have this method to make a xor between 2 NSStrings, i´m printing the result on NSLog but it isn´t the expect.
Can´t figure out what i´m doing wrong.

(void)XorSecretKeyDeviceId   
{   
NSString* secretKey = @"123";//
NSString* deviceId = @"abcdef";//

NSData* stringKey = [secretKey dataUsingEncoding:NSUTF8StringEncoding];
NSData* stringDeviceId = [deviceId dataUsingEncoding:NSUTF8StringEncoding];

unsigned char* pBytesInput = (unsigned char*)[stringKey bytes];    //Bytes
unsigned char* pBytesKey = (unsigned char*)[stringDeviceId bytes];

unsigned int vlen = [secretKey length];    //Keys Length
unsigned int klen = [deviceId length];

unsigned int v;
unsigned int k = vlen % klen;
unsigned char c;

for(v = 0; v < vlen; v++)
{
    c = pBytesInput[v] ^ pBytesKey[k];
    pBytesInput[v] = c;
    NSLog(@"%c", c);

    k = (++k < klen ? k : 0);
}
}

Answer 1

Are you setting your pBytesInput and pBytesKey variables correctly? At the moment, you have unsigned char* pBytesInput = (unsigned char*)[stringKey bytes]; (i.e. the input is the “key”), and pBytesKey is the device ID. This seems odd.

Also, be careful using UTF-8 encoding. UTF-8 uses the high bit on any byte in the string to indicate a “continuation” of a multi-byte character into the next byte. Your encoding could plausibly generate invalid UTF-8 by giving the setting the high bit of the final byte in the encryption.

For more than that, you’ll have to say what the “wrong result” is.