iOS encryption AES128/CBC/nopadding why is not working?

Question

I have an app that needs to encode some data using AES/CBC/no padding. The app is ported also on android. There the encoding is done like this:

byte[] encode         


        

Answer 1

I found the solution to my problem. In order to make the encryption work without padding i had to add 0x0000 instead of kCCOptionPKCS7Padding or kCCOptionECBMode which are treated.

Also if the data that needs to be encoded doesn't have a length multiple of kCCKeySizeAES128 ( 16 ) then the vector that holds the data must be resized to have the length multiple with kCCKeySizeAES128 and the empty values filled with something. I added spaces.

    - (NSData *)AES128EncryptWithKey:(NSString *)key
{
    char keyPtr[kCCKeySizeAES128+1];
    bzero(keyPtr, sizeof(keyPtr));

    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    int dataLength = [self length];
    int diff = kCCKeySizeAES128 - (dataLength % kCCKeySizeAES128);
    int newSize = 0;

    if(diff > 0)
    {
        newSize = dataLength + diff;
    }

    char dataPtr[newSize];
    memcpy(dataPtr, [self bytes], [self length]);
    for(int i = 0; i < diff; i++)
    {
        dataPtr[i + dataLength] = 0x20;
    }

    size_t bufferSize = newSize + kCCBlockSizeAES128;
    void *buffer = malloc(bufferSize);

    size_t numBytesEncrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt,
                                          kCCAlgorithmAES128,
                                          0x0000, //No padding
                                          keyPtr,
                                          kCCKeySizeAES128,
                                          NULL,
                                          dataPtr,
                                          sizeof(dataPtr),
                                          buffer,
                                          bufferSize,
                                          &numBytesEncrypted);

    if(cryptStatus == kCCSuccess)
    {
        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
    }

    return nil;
}