NSData+AES.h

@interface NSData (AES)

- (instancetype)aesEncryptWithKey:(NSData *)key iv:(NSData *)iv;
- (instancetype)aesDecryptWithKey:(NSData *)key iv:(NSData *)iv;

@end

NSData+AES.m

#import <CommonCrypto/CommonCryptor.h>
#import "NSData+AES.h"

@implementation NSData (AES)

- (instancetype)aesEncryptWithKey:(NSData *)key iv:(NSData *)iv
{
    return [self aesOperation:kCCEncrypt key:key iv:iv];
}

- (instancetype)aesDecryptWithKey:(NSData *)key iv:(NSData *)iv
{
    return [self aesOperation:kCCDecrypt key:key iv:iv];
}

- (instancetype)aesOperation:(CCOperation)operation key:(NSData *)key iv:(NSData *)iv
{
    if (iv && iv.length != 16) {
        @throw [NSException exceptionWithName:@"Cocoa Security"
                                       reason:@"Length of iv is wrong. Length of iv should be 16 (128bits)"
                                     userInfo:nil];
    }
    
    if (key.length != 16 && key.length != 24 && key.length != 32) {
        @throw [NSException exceptionWithName:@"Cocoa Security"
                                       reason:@"Length of key is wrong. Length of iv should be 16, 24 or 32 (128, 192 or 256bits)"
                                     userInfo:nil];
    }
    
    // Setup output buffer.
    size_t bufferSize = [self length] + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);
    
    size_t encryptedSize = 0;
    CCCryptorStatus cryptStatus = CCCrypt(operation,
                                          kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding,
                                          [key bytes],              // Key
                                          [key length],             // kCCKeySizeAES
                                          (iv ? [iv bytes] : NULL), // IV (optional)
                                          [self bytes],
                                          [self length],
                                          buffer,
                                          bufferSize,
                                          &encryptedSize);
    
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:encryptedSize];
    }
    
    free(buffer);
    
    return nil;
}

@end

Larger files crash with the memory issue.