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Department of Computer Science and Information Engineering PowerPoint Presentation
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Department of Computer Science and Information Engineering

Department of Computer Science and Information Engineering

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Department of Computer Science and Information Engineering

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

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

  8. Packed array DFA implementation

  9. Packed transition tables

  10. Packed transition tables

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

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

  13. Input compression • Pd is a set of disjoint sets of input characters

  14. Example

  15. Example (cont.)

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

  17. Evaluation Result