128 bit AES encryption returns null in Objective-C

Question

I am trying to encrypt a string using AES 128 bit encryption, but the encrypted data converted, when converted to a string, always returns null.

NSString *iv = @"fedcba9876543210";
NSString *key = @"0123456789abcdef";
- (NSData *)AES128EncryptWithKey
{
char keyPtr[kCCKeySizeAES128 + 1];
bzero( keyPtr, sizeof( keyPtr ) );

[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, kCCOptionECBMode | kCCOptionPKCS7Padding,
                                      keyPtr, kCCKeySizeAES128,
                                      NULL ,
                                      [self bytes], dataLength,
                                      buffer, bufferSize,
                                      &numBytesEncrypted );
if( cryptStatus == kCCSuccess )
{
    return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
}
}

This is my encryption function.

NSData *data = [@"String to encrypt" dataUsingEncoding:NSUTF8StringEncoding];

NSData *encryptedData = [[NSData alloc] init];

encryptedData = [data AES128EncryptWithKey];

NSLog(@"Encrypted Data Length %d", [encryptedData length]);

if (encryptedData != nil)
{
    NSString* myString;
    myString = [[NSString alloc] initWithData:encryptedData encoding:NSUTF8StringEncoding];
    NSString* newStr = [NSString stringWithUTF8String:[encryptedData bytes]];
}

After encryption, encryption data length is reported as 16 but after converting it to an NSString it returns null. If I use stringWithUTF16String to convert it, it returns like "軽ﶁែ뼐끨驂퐇". What is the issue here?

Answer 1

Finally I got it.. As Joachim suggested I used the following method and it worked..

unichar* hexChars = (unichar*)malloc(sizeof(unichar) * (data.length*2));
unsigned char* bytes = (unsigned char*)data.bytes;
for (NSUInteger i = 0; i < data.length; i++) {
    unichar c = bytes[i] / 16;
    if (c < 10) c += '0';
    else c += 'a' - 10;
    hexChars[i*2] = c;
    c = bytes[i] % 16;
    if (c < 10) c += '0';
    else c += 'a' - 10;
    hexChars[i*2+1] = c;
}
NSString* retVal = [[NSString alloc] initWithCharactersNoCopy:hexChars
                                                       length:data.length*2
                                                 freeWhenDone:YES];