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Intrusion Detection

Intrusion Detection. CIT304 University of Sunderland Harry R. Erwin, PhD. Resources. B. Schneier, 2000, Secrets and Lies, Wiley, ISBN: 0-471-25311-1. E. Amoroso, 1999, Intrusion Detection, Intrusion.net, ISBN: 0-9666700-7-8

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Intrusion Detection

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  1. Intrusion Detection CIT304 University of Sunderland Harry R. Erwin, PhD

  2. Resources • B. Schneier, 2000, Secrets and Lies, Wiley, ISBN: 0-471-25311-1. • E. Amoroso, 1999, Intrusion Detection, Intrusion.net, ISBN: 0-9666700-7-8 • R. G. Bace, 2000, Intrusion Detection, Macmillan Technical Publishing, ISBN: 1-57870-185-6 • We will mostly follow Schneier in this lecture.

  3. Intrusion Detection Systems (IDS) • Network Monitors—watch your network looking for suspicious behavior • Often but not always based on Audit • Provide reactive rather than proactive security • Alert on successful and ongoing attacks • Need to be accurate in detecting attacks and in determining that an attack is not underway. • Also may provide diagnosis tools.

  4. The False Alarm Problem • Base rate fallacy—suppose you have a test that is 99% accurate. Is this good? Not necessarily! • Suppose the real attack rate is 1x10-6 per packet and there are 100,000,000 packets a day. This test will generate 10,000 false positives (100 per day) for every real attack it detects (about 4 per year). (Work it out…) • If network attacks are rare, a test has to be powerful to be useful. • Hint: this is a likely exam question.

  5. The Timely Notification Problem • You may want to be warned in time to do something, but… • What about slow attacks, running over hours or days? When should the IDS become suspicious and tell you? • What about ambiguous evidence? Do you really want to be warned about borderline cases?

  6. The Response Problem • What do you do if you do hear an alarm? I.e., the current problem with giving out general warnings of terrorist activity. • Options include: • Wait • Collect more information • Do something • Hope it goes away • You may be too busy fighting alligators to do anything intelligent about draining the swamp.

  7. Approaches to Building an IDS • Misuse detection • IDS knows what an attack looks like and looks for it. • “Network virus scanner” • Fast, easy to build, has a low false positive rate. • Misses a lot and is easy to fool. • Probably will get better over time.

  8. Approaches to Building an IDS (II) • Anomaly detection • Generates a statistical or neural network model of the network to figure out what is normal • Sounds an alarm for abnormal activity • Uses AI: • Bayesian statistics • Neural networks • Expert systems

  9. Problems with Anomaly Detection • Does the training data include an attack? Then hacking will be considered normal. 8( • New things happen on networks all the time. Successful retraining of an existing AI system to handle this is a hard problem, worth a PhD. 8( • How can it categorize attacks? That requires expert input. 8( • False positives are much higher. 8( • Attack indicators are brittle, so that hackers can sneak past them. 8(

  10. Inline versus Audit-Based IDS • Should the IDS detect attacks in real-time or using audit log processing? • Inline will have incomplete data. • Inline is also computationally expensive. • Audit log processing is after the fact. • Audit log formats vary quite a bit. • A combined approach is feasible, but costly.

  11. Host-Based versus Network-Based IDS • Network-based IDS is basically wire-tapping • Stealthy • Operating-system independent • Host-based IDS uses audit logs • From workstations, servers, switches, routers, etc. • Product-specific.

  12. Make or Buy • Do your own monitoring or pay someone else? • Counterpane • Qinetiq • Trust issues particularly important. • In-house expertise requirement.

  13. Honey Pots and Burglar Alarms • Burglar alarms are resources on the network that generate an alarm if accessed incorrectly. • Honey pots are burglar alarms dressed up to look attractive. May incorporate subnetworks and dummy computers. • Costly. • Have to look real to the attackers. • Legality important. Entrapment may be an issue, so intruders must be warned. • Read http://csrc.nist.gov/publications/secpubs/berferd.ps • See also http://www.strategypage.com/fyeo/howtomakewar/default.asp?target=HTIW.HTM

  14. Incident Handling Issues • Be prepared • Have procedures • Don’t panic • When to call in the police? • Expectation management • Damage control • Dealing with witch hunts

  15. IDS Requirements • Must be: • Effective • Easy to use • Adaptable • Robust • Fast • Efficient • Safe

  16. Future IDS Needs • Should be: • Accommodating • Security enhancing • Scalable • Realistic • Hardened

  17. Conclusions • We aren’t there yet, • But any IDS system is better than none at all. • This is the place to be if you want to work on secure systems development.

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