AES Decryption has different behavior in iOS 7 than iOS 8/9

The following method returns different results when run on iOS 7 than on iOS 8/9.

+ (NSData *)decryptData:(NSData *)data key:(NSData *)key iv:(NSData *)iv;
{
  NSData *result = nil;

  // setup key
  unsigned char cKey[FBENCRYPT_KEY_SIZE];
  bzero(cKey, sizeof(cKey));
  [key getBytes:cKey length:FBENCRYPT_KEY_SIZE];

  // setup iv
  char cIv[FBENCRYPT_BLOCK_SIZE];
  bzero(cIv, FBENCRYPT_BLOCK_SIZE);
  if (iv) {
    [iv getBytes:cIv length:FBENCRYPT_BLOCK_SIZE];
  }

  // setup output buffer
  size_t bufferSize = [data length] + FBENCRYPT_BLOCK_SIZE;
  void *buffer = malloc(bufferSize);

  // do decrypt
  size_t decryptedSize = 0;
  CCCryptorStatus cryptStatus =
      CCCrypt(kCCDecrypt, FBENCRYPT_ALGORITHM, kCCOptionPKCS7Padding, cKey,
              FBENCRYPT_KEY_SIZE, cIv, [data bytes], [data length], buffer,
              bufferSize, &decryptedSize);

  if (cryptStatus == kCCSuccess) {
    result = [NSData dataWithBytesNoCopy:buffer length:decryptedSize];
  } else {
    free(buffer);
    NSLog(@"[ERROR] failed to decrypt| CCCryptoStatus: %d", cryptStatus);
  }

  return result;
}

      

        
        
        
      

    

Encryption works on iOS 7/8/9. But the result of decrypting nil on iOS 7.

decryptedSize

equals 0 after execution. Elements buffer

remain 0.

Some definitions

#define FBENCRYPT_ALGORITHM kCCAlgorithmAES128
#define FBENCRYPT_BLOCK_SIZE kCCBlockSizeAES128
#define FBENCRYPT_KEY_SIZE kCCKeySizeAES256

      

        
        
        
      

    

I have read answers to similar questions CCCrypt()

on SO. Tried the following:

• Increase cKey
  
  length by 1
• Extend the length cKey
  
  toFBENCRYPT_KEY_SIZE * 2 + 1
  
  
• Set the first byte cKey
  
  to 0 (some say iOS 6 does this when getting the key bytes from the NSString)

None of the above works.

I come back with some sample data when the method is called.

Three parameters passed to decryptData

:

• Details: ea1e6896 b5731f40 1d560a18 f0729fa6
  
  ,
• : 17c76e90 9a6fef8d b1fd45fa 2de18db0 d2236264 db6c8a60 125599ec 2dfb5614
  
  , 256 bit for AES256
• iv:, 41463531 38453234 44333835 42463636
  
  16-byte which is the same block size

Expected output (and actual output on iOS8 / 9) 248e51af 66bf85d3 00003ab6 fe3c0000

.