Approximate reduction of finite automata for high-speed network intrusion detection

• Published in: International journal on software tools for technology transfer Vol. 22; no. 5; pp. 523 - 539
• Main Authors: Češka, Milan, Havlena, Vojtěch, Holík, Lukáš, Lengál, Ondřej, Vojnar, Tomáš
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.10.2020; Springer Nature B.V
• Subjects: Automata theory; Communications traffic; Computer Science; Error detection; Intrusion detection systems; Regular Paper; Size reduction; Software Engineering; Software Engineering/Programming and Operating Systems; Statistical analysis; Theory of Computation; Reduction; Nondeterministic finite automata; Deep packet inspection; High-speed network monitoring
• ISSN: 1433-2779; 1433-2787
• DOI: 10.1007/s10009-019-00520-8

We consider the problem of approximate reduction of non-deterministic automata that appear in hardware-accelerated network intrusion detection systems (NIDSes). We define an error distance of a reduced automaton from the original one as the probability of packets being incorrectly classified by the reduced automaton (wrt the probabilistic distribution of packets in the network traffic). We use this notion to design an approximate reduction procedure that achieves a great size reduction (much beyond the state-of-the-art language-preserving techniques) with a controlled and small error. We have implemented our approach and evaluated it on use cases from Snort , a popular NIDS. Our results provide experimental evidence that the method can be highly efficient in practice, allowing NIDSes to follow the rapid growth in the speed of networks.