  Deep learning based intrusion detection systems (DL-based IDS) have emerged
as one of the best choices for providing security solutions against various
network intrusion attacks. However, due to the emergence and development of
adversarial deep learning technologies, it becomes challenging for the adoption
of DL models into IDS. In this paper, we propose a novel IDS architecture that
can enhance the robustness of IDS against adversarial attacks by combining
conventional machine learning (ML) models and Deep Learning models. The
proposed DLL-IDS consists of three components: DL-based IDS, adversarial
example (AE) detector, and ML-based IDS. We first develop a novel AE detector
based on the local intrinsic dimensionality (LID). Then, we exploit the low
attack transferability between DL models and ML models to find a robust ML
model that can assist us in determining the maliciousness of AEs. If the input
traffic is detected as an AE, the ML-based IDS will predict the maliciousness
of input traffic, otherwise the DL-based IDS will work for the prediction. The
fusion mechanism can leverage the high prediction accuracy of DL models and low
attack transferability between DL models and ML models to improve the
robustness of the whole system. In our experiments, we observe a significant
improvement in the prediction performance of the IDS when subjected to
adversarial attack, achieving high accuracy with low resource consumption.
