function create_hash($password)
    {
        
        // format: algorithm:iterations:salt:hash
        //$salt = base64_encode(mcrypt_create_iv(PBKDF2_SALT_BYTES, MCRYPT_DEV_URANDOM));

        $encrypt_method = "AES-256-CBC";
        $key = hash('sha256', $secret_key);
        $iv = substr(hash('sha256', $secret_iv), 0, 16);

        $salt = base64_encode(openssl_encrypt($string, $encrypt_method, $key, 0, $iv));
        return PBKDF2_HASH_ALGORITHM . ":" . PBKDF2_ITERATIONS . ":" .  $salt . ":" .
        base64_encode($this->pbkdf2(
            PBKDF2_HASH_ALGORITHM,
            $password,
            $salt,
            PBKDF2_ITERATIONS,
            PBKDF2_HASH_BYTES,
            true
        ));
    }