initWithData returns (null)

Well, I have a code that selects a text, and converts it to NSData then encrypts it with AES-256 and then converts this NSData to a NSString to be displayed the message encrypted, I'm doing this as follows:

 NSString *text = @"This is a simple text";

    NSData* data = [text dataUsingEncoding:NSUTF8StringEncoding];

    NSData *dataEnc = [data AES256EncryptWithKey:@"12556"];

    NSString *stringCrypt = [[NSString alloc] initWithData:dataEnc encoding:NSUTF8StringEncoding];

    NSData *dataDesc = [dataEnc AES256DecryptWithKey:@"12556"];

    NSString *string = [[NSString alloc] initWithData:dataDesc encoding:NSUTF8StringEncoding];

    NSLog(@"Text normal -> %@",text);

    NSLog(@"Text with AES -> %@",stringCrypt);

    NSLog(@"Text with AES decrypted -> %@",string);

The output of my NSLog is:

Text normal -> this is a simple text 
Text with AES -> (null) 
Text With AES decrypted -> this is a simple text

So the problem is with the code:

NSString *stringCrypt = [[NSString alloc] initWithData:dataEnc encoding:NSUTF8StringEncoding];

That return a null string, and in this case I need that string that will be inserted into a text file, how to solve this problem? why this returning a null value?

EDIT

The function to convert it to AES256 is:

- (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];

    //See the doc: For block ciphers, the output size will always be less than or
    //equal to the input size plus the size of one block.
    //That's why we need to add the size of one block here
    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;
}

Solved

As the user Zaph says, I need to use the -base64EncodedDataWithOptions , in my case I do as follows:

NSString *text = @"This is a simple text";

    NSData* data = [text dataUsingEncoding:NSUTF8StringEncoding];

    NSData *dataEnc = [data AES256EncryptWithKey:@"12556"];

    NSData *daes = [dataEnc base64EncodedDataWithOptions:NSDataBase64Encoding64CharacterLineLength];

    NSString *stringCrypt = [[NSString alloc] initWithData:daes encoding:NSUTF8StringEncoding];

    NSData *decodedData = [[NSData alloc] initWithBase64EncodedString:stringCrypt options:0];

    NSData *dataDesc = [decodedData AES256DecryptWithKey:@"12556"];

    NSString *string = [[NSString alloc] initWithData:dataDesc encoding:NSUTF8StringEncoding];

    NSLog(@"Text Normal -> %@",text);

    NSLog(@"Text with AES (BASE64) -> %@",stringCrypt);

    NSLog(@"Text with AES decrypted -> %@",string);

In this case I only need to convert it to a base64 string, and now I can store this values inside a text value, and other device can get this text and decrypt. Thanks for all.

---

Random bytes, and that is what encrypted looks like and can not be distinguished from, rarely is convertible to a string. This is why encrypted data is often Base64 encoded to produce printable characters.

Use - base64EncodedStringWithOptions: to encode the encrypted data to a character string.

---

I expect your initWithData is failing because dataEnc most certainly does not contain UTF8 bytes. Assuming your AES256 encryption code is working correctly, it is going to return binary data that looks essentially random. It will not be realistically convertible to a string unless you do something like go through it byte by byte and output hex values.

You can write the encrypted NSData to a file directly using one of its writeToFile methods.

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