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Signature Based and Anomaly Based Network Intrusion Detection

Signature Based and Anomaly Based Network Intrusion Detection . By Stephen Loftus and Kent Ho CS 158B . Agenda. Introduce Network Intrusion Detection (NID) Signature Anomaly Compare and Contrast: Signature based vs. Anomaly based NID Example using Ethereal ™.

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Signature Based and Anomaly Based Network Intrusion Detection

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  1. Signature Based and Anomaly Based Network Intrusion Detection By Stephen Loftus and Kent Ho CS 158B

  2. Agenda • Introduce Network Intrusion Detection (NID) • Signature • Anomaly • Compare and Contrast:Signature based vs. Anomaly based NID • Example using Ethereal™

  3. Intrusion Detection Systems • Intrusion detection begins where the firewall ends. • Preventing unauthorized entry is best, but not always possible. • It is important that the system is reliable and accurate and secure.

  4. IDS (cont.) • When designing a IDS, the mission is to protect the data’s • Confidentiality- read • Integrity- read/write • Availability- read/write/access • Threats can come from both outside and inside the network.

  5. Signature • Signature based IDS are based on looking for “known patterns” of detrimental activity. • Benefits: • Low alarm rates: All it has to do is to look up the list of known signatures of attacks and if it finds a match report it. • Signature based NID are very accurate. • Speed: The systems are fast since they are only doing a comparison between what they are seeing and a predetermined rule.

  6. Signature (cont.) • Negatives: • If someone develops a new attack, there will be no protection. • “only as strong as its rule set.” • Attacks can be masked by splitting up the messages. • Similar to Anti-Virus, after a new attack is recorded, the data files need to be updated before the network is secure. • Example: • Port Scan • DOS • Sniffing

  7. Anomaly • Anomaly based IDS are based on tracking unknown unique behavior pattern of detrimental activity • Advantages: • Helps to reduce the “limitations problem”. • Conducts a thorough screening of what comes through.

  8. Anomaly (cont.) • Disadvantages: • False positives,catches too much because Behavior based NIDs monitor a system based on their behavior patterns. • Painstaking slow to do an exhaustive monitoring, uses up a lot or resourceAfter an anomaly has been detected, it may become a “signature”.

  9. Anomaly vs. Signature • Which is the best way to defend your network? • Both have advantages • Signature can be used as a stand alone system • Anomaly has a few weak points that prevent it from being a stand alone system. • Signature is the better of the two for defending you network • The best way is to use both!

  10. Example • Using Ethereal™ to detect a port scan • A port scan is when a person executes sequential port open requests trying to find an open port. Most of these come back with a “reset” • Normal TCP/IP port request • Port request on closed port

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