Improving NFA-Based Signature Matching Using Ordered Binary Decision Diagrams

Network intrusion detection systems (NIDS) make extensive use of regular expressions as attack signatures. Internally, NIDS represent and operate these signatures using finite automata. Existing representations of finite automata present a wellknown time-space tradeoff: Deterministic automata (DFAs) provide fast matching but are memory intensive, while non-deterministic automata (NFAs) are space-efficient but are several orders of magnitude slower than DFAs. This time/space tradeoff has motivated much recent research, primarily with a focus on improving the space-efficiency of DFAs, often at the cost of reducing their performance. This paper presents NFA-OBDDs, a symbolic representation of NFAs that retains their spaceefficiency while improving their time-efficiency. Experiments using Snort HTTP and FTP signature sets show that an NFA-OBDD-based representation of regular expressions can outperform traditional NFAs by up to three orders of magnitude and is competitive with a varian...

• Type: Journal
• Year: 2010
• Where: RAID
• Authors: Liu Yang, Rezwana Karim, Vinod Ganapathy, Randy Smith
• Keywords: Computer Networks, NFAs, RAID 2010, Signature, finite Automata