Question

I am encrypting a text string using the following block of code.
This code relates to a method for AES256EncryptWithKey, but when I run the project, and I click on the button that uses this code, I get an uncaught exception and a warning. The warning says: “NSString may not respond to: ‘-AES256EncryptWithKey'”. What can I do? Is it possible to put a chunk of code in that handles exceptions? Or is it something totally different?

NSString *Input  = [Inputbox text];
    [Input AES256encryptWithKey];

Here is the code I have used, that relates to AES256EncryptWithKey:

@implementation NSData (AES256)

- (NSData *)AES256EncryptWithKey:(NSString *)key {
    // 'key' should be 32 bytes for AES256, will be null-padded otherwise
    char keyPtr[kCCKeySizeAES256+1]; // room for terminator (unused)
    bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)

    // fetch key data
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    NSUInteger dataLength = [self length];

    size_t bufferSize = dataLength + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);

    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
                                          keyPtr, kCCKeySizeAES256,
                                          NULL /* initialization vector (optional) */,
                                          [self bytes], dataLength, /* input */
                                          buffer, bufferSize, /* output */
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        //the returned NSData takes ownership of the buffer and will free it on deallocation
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }

    free(buffer); //free the buffer;
    return nil;
}

Thank-You in advance. Links, Tutorials, Answers, and anything else is appreciated.

Answer 1

Thats because NSString in fact does not respond to that message – your code adds a category to NSData!

Remember encryption works on binary data, so you must convert your potentially unicode NSString into a well-defined binary encoding (say, UTF-8)

The fastest conversion is to use the NSString dataWithEncoding method.