1. 1 Regular expression matching with input compression ： a hardware design for use within network intrusion detection systems Department of Computer Science and Information Engineering National Cheng Kung University, Taiwan R.O.C. Authors: Gerald Tripp Publisher: Journal in Computer Virology, 19 March 2007 Present: Yu-Tso Chen Date: November, 22, 2007

2. 2 Outline 1. Introduction 2. Definitions and problem description 3. Matching of Individual Patterns 4. Selective Grouping of Multiple Patterns 5. Evaluation Result 6. Conclusion

3. 3 Introduction Build a table based automata implement- ation but to use a form of input compression The table based approach allow the system to be dynamically updated at run time The input compression helps to make significant reductions in the automata memory requirements.

4. 4 Outline 1. Introduction 2. Definitions and problem description 3. Matching of Individual Patterns 4. Selective Grouping of Multiple Patterns 5. Evaluation Result 6. Conclusion

5. 5 Definitions and problem description Simple table based implementations can require quite a lot of memory resources REs themselves that often create automata with more node (and edges) Tables required for implementing automata can have a high level of redundancy

6. 6 Definitions and problem description (cont.) For a Mealy machine, the amount of memory M in bits for a DFA with s states, i input bits and o output bits

7. 7 Outline 1. Introduction 2. Definitions and problem description 3. Regular expression implementation 4. Input compression 5. Evaluation Result

8. 8 Packed array DFA implementation

9. 9 Packed transition tables

10. 10 Packed transition tables

11. 11 Outline 1. Introduction 2. Definitions and problem description 3. Regular expression implementation 4. Input compression 5. Evaluation Result

12. 12 Input compression E sn as the set of characters enabling the edge or edges between current state s and next state n Complete set of edge sets P a P a gives us the sets of characters that we are interested in for all DFA edges. These sets may however have overlaps

13. 13 Input compression P d is a set of disjoint sets of input characters

14. 14 Example

15. 15 Example (cont.)

16. 16 Outline 1. Introduction 2. Definitions and problem description 3. Regular expression implementation 4. Input compression 5. Evaluation Result

17. 17 Evaluation Result