CCCrypt encrypted with ios5 can't be decrypted with ios6 - objective-c

Question

My cocos2d game saves data using CCCrypt() encryption. I use the mac address as the encryption key. The save file encrypted in IOS5 can't decrypt with the same mac address in IOS6. That means that a user who updated their game will lose all their data!
Is there any way to decrypt the old file?
Here's code:
#implementation NSData (AESAdditions)
- (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;
}
- (NSData *)AES256DecryptWithKey:(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 numBytesDecrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
keyPtr, kCCKeySizeAES256,
NULL /* initialization vector (optional) */,
[self bytes], dataLength, /* input */
buffer, bufferSize, /* output */
&numBytesDecrypted);
if (cryptStatus == kCCSuccess) {
//the returned NSData takes ownership of the buffer and will free it on deallocation
return [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
}
free(buffer); //free the buffer;
return nil;
}
#end

Answer 1

You'd need to give details on how you implemented your encryption, particularly what options you used.
The most common cause of failed decrypts on iOS 6 in my experience is the CTR bug that they changed/fixed. In iOS 5, there was the option kCCModeOptionCTR_LE which was a lie. It actually encrypted with kCCModeOptionCTR_BE. In iOS 6, they fixed this, and if you try to used kCCModeOptionCTR_LE you'll get an "unimplemented" error. But CCCrypt() doesn't generally use CTR mode, so I don't know if this applies.

Answer 2

Ok, I found the solution.
Key point here:
I add two methods to NSData to encrypt and decrypt with code based IOS5 lib.
#implementation NSData (AESAdditions)
-(NSData*)AES256EncryptWithKey:(NSString*)key;
-(NSData *)AES256DecryptWithKey:(NSString *)key
Now in IOS6 lib,NSData might be changed,so two methods worked different,it can't decrypt the file encrypt in IOS5.
In my code based IOS6,I wrote methods in my class.
like this:
- (NSData*)AES256EncryptWithKey:(NSString*)key data:(NSData *)data;
- (NSData *)AES256DecryptWithKey:(NSString *)key data:(NSData *)data;
the code work well same as in IOS5.