Rethinking Robust and Accurate Application Protocol Identification: A Nonparametric Approach

Protocol traffic analysis is important for a variety of networking and security infrastructures, such as intrusion detection and prevention systems, network management systems, and protocol specification parsers. In this paper, we propose ProHacker, a nonparametric approach that extracts robust and accurate protocol keywords from network traces and effectively identifies the protocol trace from mixed Internet traffic. ProHacker is based on the key insight that the n-grams of protocol traces have highly predictable statistical nature that can be effectively captured by statistical language models and leveraged for robust and accurate protocol identification. In ProHacker, we first extract protocol keywords using a nonparametric Bayesian statistical model, and then use the corresponding protocol keywords to classify protocol traces by a semi-supervised learning algorithm. We implement and evaluate ProHacker on real-world traces, including SMTP, FTP, PPLive, SopCast, and PPStream, and our experimental results show that ProHacker can accurately identify the protocol trace with an average precision of about 99.42% and an average recall of about 98.64%. We also compare the results of ProHacker to two state-of-the-art approaches ProWord and Securitas using backbone traffic. We show that ProHacker provides significant improvements on precision and recall for online protocol identification.