A DFA with Extended Character-Set for Fast Deep Packet Inspection

Abstract

Deep packet inspection (DPI), based on regular expressions, is expressive, compact, and efficient in specifying attack signatures. We focus on their implementations based on general-purpose processors that are cost-effective and flexible to update. In this paper, we propose a novel solution, called deterministic finite automata with extended character-set (DFA/EC), which can significantly decrease the number of states through doubling the size of the character-set. Unlike existing state reduction algorithms, our solution requires only a single main memory access for each byte in the traffic payload, which is the minimum. We perform experiments with several Snort rule-sets. Results show that, compared to DFAs, DFA/ECs are very compact and are over four orders of magnitude smaller in the best cases; DFA/ECs also have smaller memory bandwidth and run faster. We believe that DFA/EC will lay a groundwork for a new type of state compression technique in fast packet inspection.