  As malicious cyber threats become more sophisticated in breaching computer
networks, the need for effective intrusion detection systems (IDSs) becomes
crucial. Techniques such as Deep Packet Inspection (DPI) have been introduced
to allow IDSs analyze the content of network packets, providing more context
for identifying potential threats. IDSs traditionally rely on using
anomaly-based and signature-based detection techniques to detect unrecognized
and suspicious activity. Deep learning techniques have shown great potential in
DPI for IDSs due to their efficiency in learning intricate patterns from the
packet content being transmitted through the network. In this paper, we propose
a revolutionary DPI algorithm based on transformers adapted for the purpose of
detecting malicious traffic with a classifier head. Transformers learn the
complex content of sequence data and generalize them well to similar scenarios
thanks to their self-attention mechanism. Our proposed method uses the raw
payload bytes that represent the packet contents and is deployed as
man-in-the-middle. The payload bytes are used to detect malicious packets and
classify their types. Experimental results on the UNSW-NB15 and CIC-IOT23
datasets demonstrate that our transformer-based model is effective in
distinguishing malicious from benign traffic in the test dataset, attaining an
average accuracy of 79\% using binary classification and 72\% on the
multi-classification experiment, both using solely payload bytes.
