AES128 truncated decrypted text on iOS 7, no problem with iOS 8

Using ciphertext encrypted with AES128 using ECB mode (this is toy encryption) and PKCS7 addon, the following codeblock results in full plaintext being recovered under iOS 8.

Running the same code block in iOS 7 results in the correct plaintext but is truncated. Why is this?

#import "NSData+AESCrypt.h" // <-- a category with the below function
#import <CommonCrypto/CommonCryptor.h>

- (NSData *)AES128Operation:(CCOperation)operation key:(NSString *)key iv:(NSString *)iv
{
    char keyPtr[kCCKeySizeAES128 + 1];
    bzero(keyPtr, sizeof(keyPtr));
    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    char ivPtr[kCCBlockSizeAES128 + 1];
    bzero(ivPtr, sizeof(ivPtr));
    if (iv) {
        [iv getCString:ivPtr maxLength:sizeof(ivPtr) encoding:NSUTF8StringEncoding];
    }

    NSUInteger dataLength = [self length];                      
    size_t bufferSize = dataLength + kCCBlockSizeAES128;        
    void *buffer = malloc(bufferSize);

    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(operation,
                                          kCCAlgorithmAES128,
                                          kCCOptionPKCS7Padding | kCCOptionECBMode,
                                          keyPtr,               
                                          kCCBlockSizeAES128,   
                                          ivPtr,                
                                          [self bytes],
                                          dataLength,           
                                          buffer,
                                          bufferSize,           
                                          &numBytesEncrypted);  
    if (cryptStatus == kCCSuccess) {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }
    free(buffer);
    return nil;
}

      

        
        
        
      

    

I have added a standalone test harness below with the results.

Wire harness:

NSString *key = @"1234567890ABCDEF";
NSString *ciphertext = @"I9JIk5BskZMZKJFB/EAs+N2AYzkVR15DoBbUL7cBydBkWGlujVnzRHvBNvSVbcKh";

NSData *encData = [[NSData alloc]initWithBase64EncodedString:ciphertext options:0];
NSData *plainData = [encData AES128Operation:kCCDecrypt key:key iv:nil];

NSString *plaintext = [NSString stringWithUTF8String:[plainData bytes]];

DLog(@"key: %@\nciphertext: %@\nplaintext: %@", key, ciphertext, plaintext);

      

        
        
        
      

    

iOS 8 results:

key: 1234567890ABCDEF
ciphertext: I9JIk5BskZMZKJFB/EAs+N2AYzkVR15DoBbUL7cBydBkWGlujVnzRHvBNvSVbcKh
plaintext: the quick brown fox jumped over the fence

      

        
        
        
      

    

IOS 7 results:

key: 1234567890ABCDEF
ciphertext: I9JIk5BskZMZKJFB/EAs+N2AYzkVR15DoBbUL7cBydBkWGlujVnzRHvBNvSVbcKh
plaintext: the quick brown fox jumped over 0

      

        
        
        
      

    

and subsequent results:

plaintext: the quick brown fox jumped over 
plaintext: the quick brown fox jumped over *

      

        
        
        
      

    

Update: Guess Me: When I Change

kCCOptionPKCS7Padding | kCCOptionECBMode ⇒ kCCOptionECBMode

results in iOS 7 are expected. Why is this?? I know the byte count is block aligned because the ciphertext is padded with PKCS7 padding, so it makes sense, but why does the setting kCCOptionPKCS7Padding | kCCOptionECBMode

cause truncated behavior in iOS 7?

Edit: The test ciphertext above was generated both from this website and independently using PHP mcrypt with manual PKCS7 in the following function:

function encryptAES128WithPKCS7($message, $key)
{
    if (mb_strlen($key, '8bit') !== 16) {
        throw new Exception("Needs a 128-bit key!");
    }

    // Add PKCS7 Padding
    $block = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128);
    $pad = $block - (mb_strlen($message, '8bit') % $block);
    $message .= str_repeat(chr($pad), $pad);

    $ciphertext = mcrypt_encrypt(
        MCRYPT_RIJNDAEL_128,
        $key,
        $message,
        MCRYPT_MODE_ECB
    );

    return $ciphertext;
}

// Demonstration encryption
echo base64_encode(encryptAES128WithPKCS7("the quick brown fox jumped over the fence", "1234567890ABCDEF"));

      

        
        
        
      

    

Of:

I9JIk5BskZMZKJFB / EA + N2AYzkVR15DoBbUL7cBydBkWGlujVnzRHvBNvSVbcKh

Update: Correct PICCS # 7 cipher ciphertext would be

I9JIk5BskZMZKJFB / EA + N2AYzkVR15DoBbUL7cBydA6aE5a3JrRst9Gn3sb3heC

This is why this is not the case.