Efficient signature matching with multiple alphabet compression tables
Shijin Kong, Randy Smith, Cristian Estan · 2008
Signature matching is a performance critical operation in intrusion prevention systems. Modern systems express signatures as regular expressions and use Deterministic Finite Automata (DFAs) to efficiently match them against the input. In principle, DFAs can be combined so that all signatures can be examined in a single pass over the input. In practice, however, combining DFAs corresponding to intrusion prevention signatures results in memory requirements that far exceed feasible sizes. We observe for such signatures that distinct input symbols often have identical behavior in the DFA. In these cases, an Alphabet Compression Table (ACT) can be used to map such groups of symbols to a single symbol to reduce the memory requirements.