iOS Encrypt/Decrypt Need Guidance

Question

I need to encrypt/decrypt data using AES-128-CBC on my project. I got reference from here which I have implemented in my project. But from the available code, I couldn't get thru [self length] and [self bytes] lines, hence I added a parameter to the function and implemented the same. Those lines are using NSData values, but I get 'No visible ... '. I am stuck in step 3 i.e. adding code in class where I want to call the Encrypt method. MY code :

HEADER

@interface MC_AES : NSObject

- (NSData*)AES128Decrypt : (NSData*) inputData;
- (NSData*)AES128Encrypt : (NSData*) inputData;

@end

IMPLEMENTATION

#include <CommonCrypto/CommonCryptor.h>
#import "MC_AES.h"


NSString *iv = @"DFR55d+.njT]W-WW";
NSString *key = @"HGYJ4RXc{Kd@5q4+";

@implementation MC_AES

-(NSData*)AES128Encrypt  : (NSData*) inputData
{
    char ivPtr[kCCKeySizeAES128 + 1];
    bzero(ivPtr, sizeof(ivPtr));

    // fetch iv data
    [iv getCString:ivPtr maxLength:sizeof(ivPtr) encoding:NSUTF8StringEncoding];


    // 'key' should be 32 bytes for AES256, will be null-padded otherwise
    char keyPtr[kCCKeySizeAES128 + 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 = [inputData 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, 0,
                                          keyPtr, kCCKeySizeAES128,
                                          ivPtr/* initialization vector (optional) */,
                                          [inputData 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;
}

CODE in class where I want to call Encrypt method

// I need to encrypt password, so will have to convert password to hex value and pass here to Encrypt
- (void) testActuallyEncrypting :(NSString*) hexString {
    NSLog(@"Encrypted HexString : %@", hexString); // password in hex value

    // Convert hex to NSData object
    NSData *data = [self dataFromHexString:hexString];

    // Prepare the NSDAta obj to store the encrypted pswd
    NSData *encryptedData = [NSData dataWithBytes:[data bytes] length:[data length]];

    // ***** How can I access this here ??
    //NSData *decryptedData = [encryptedData AES128Decrypt];
    //NSString *decryptedString = [NSString stringWithUTF8String:[decryptedData bytes]];
    //NSLog(@"Decrypted String : %@", decryptedString);
    .......
    ........
}

My Query - How can I access AES128Decrypt method - (1) I got to pass it a parameter of (data) I believe i.e. the data that I need to encrypt. (2) Without creating an object of the class or its not even static how can I call this method ?

Importantly, I need to clear confirm with the signature of AES128Encrypt/AES128Decrypt methods, and the way for calling it. I am not able to understand how to handle this and make it working.

If you can help in getting thru [self length] and [self bytes] lines, then also I am fine. I just want to make it working. You may please refer the link for more code. Also I believe this code is proper for implementing AES-128-CBC encryption. Any help is highly appreciated. Thanks.

UPDATE 1 :

As I am with using standalone class MC_AES, I tried to call AES128Encrypt as follows :

- (void) testActuallyEncrypting :(NSString*) str {
    NSLog(@"String to Encrypt : %@", str);

    //Convert NSString to NSData
    NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];  //[self dataFromHexString:hexString];
    NSData *encryptedData = [NSData dataWithBytes:[data bytes] length:[data length]];
    MC_AES *aes = [[MC_AES alloc]init];

    encryptedData = [aes AES128Encrypt:data];

    NSString * encryptedStr = [NSString stringWithUTF8String:[encryptedData bytes]];
    NSLog(@"Encrypted data - %@", encryptedStr);

The encryptedData that is get is 0. In AES128Encrypt method, the cryptStatus == kCCsuccess, inputData and buffer is of size 6 & numBytesEncrypted is 0. Why I don't receive proper encrypted value ? Where am I going wrong ?

Answer 1

Follow the instructions including the comments on the code you chose to use. The implementation creates a category on NSData, read-up on Objective-C categories is you are going to use them. You might consider using code that is not a category but a standalone class.

The [self length] and [self bytes] refer to the data because the code you chose implements the encryption/decryption as a category on NSData.

There is no need to convert the password to hex and then to data, just use

- (NSData *)dataUsingEncoding:(NSStringEncoding)encoding

NSData *encryptedData = [NSData dataWithBytes:[data bytes] length:[data length]];  

Does not call the encryption method.
You never called the AES128Encrypt method.