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CMSC 414 Computer and Network Security

CMSC 414 Computer and Network Security. Jonathan Katz. Introduction and overview. What is computer/network security? Why is it important? Course philosophy and goals Course organization and information High-level overview of topics A broad perspective on “computer security”. “Security”.

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CMSC 414 Computer and Network Security

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  1. CMSC 414Computer and Network Security Jonathan Katz

  2. Introduction and overview • What is computer/network security? Why is it important? • Course philosophy and goals • Course organization and information • High-level overview of topics • A broad perspective on “computer security”

  3. “Security” • Most of computer science is concerned with achieving desired behavior • Security is concerned with preventing undesired behavior • Different way of thinking! • An enemy/opponent/hacker/adversary who is actively and maliciously trying to circumvent any protective measures you put in place

  4. One illustration of the difference • Software testing determines whether a given program implements a desired functionality • Test I/O characteristics • Q/A • How do you test whether a program does not allow for undesired functionality? • Penetration testing helps, but only up to a point

  5. Security is interdisciplinary • Draws on all areas of CS • Theory (especially cryptography) • Networking • Operating systems • Databases • AI/learning theory • Computer architecture/hardware • Programming languages/compilers • HCI, psychology

  6. Fortunately, we are winning the security battle • Strong cryptography • Firewalls, intrusion detection, virus scanners • Buffer overflow detection/prevention • User education

  7. Really??! Security incidents (reported)

  8. Philosophy of this course • We are not going to be able to cover everything • We are not going to be able to even mention everything • Main goals • A sampling of many different aspects of security • The security “mindset” • Become familiar with basic acronyms (RSA, SSL, PGP, etc.), and “buzzwords” (phishing, …) • Become an educated security consumer • Try to keep it interesting with real-world examples and “hacking” projects You will not be a security expert after this class (after this class, you should realize why it would be dangerous to think you are) You should have a better appreciation of security issues after this class

  9. Course Organization

  10. Administrative • Me • TA • Contact information, office hours, listed on course webpage

  11. Course webpage http://www.cs.umd.edu/~jkatz/security/f09 • Syllabus • Subject to change… • Slides will be posted for convenience, but they are not a substitute for attending lecture • Assigned readings • Homeworks distributed from the course webpage • Check frequently for announcements

  12. Course blog http://cmsc414.wordpress.com • I will post after each lecture • Students can post questions/comments about the lecture • Today: post a “hello” message, and answer the question: “What do you hope to get from the course?” • I will post for each homework • Students can post questions • I will post links to interesting news articles, papers, etc.

  13. Textbook • Recommended text: • “Network Security…” by Kaufman, Perlman, and Speciner (most recent edition) • Will only be used for a portion of the course • Several other good texts out there • Ask me if you are interested • Will supplement with other readings (distributed on class webpage)

  14. Class participation and readings • Research papers and news articles will be posted on the course webpage • Read these before class and come prepared to discuss • Material from these readings is fair game for the exams, even if not covered in class • Several readings already assigned

  15. Course requirements • Homeworks • About 4-5 throughout the semester • Programming portion will be done with a partner • Each student will receive a computer account • You should have already been assigned a GRACE account

  16. Syllabus (tentative)

  17. Syllabus I • Introduction… • Is security achievable…? • A broad perspective on security • Cryptography • The basics (take CMSC 456 or read my book for more) • If you took 456 with me, you can skip • Cryptography is not the whole solution… • …but it is an important part of the solution • Along the way, we will see why cryptography can’t solve all security problems

  18. Syllabus II • System security • General principles • Security policies • Access control • OS security • “Trusted computing” • Programming language security • Buffer overflows, input validation errors • Viruses/worms

  19. Syllabus III • Network security • Identity, PKI • Authentication and key exchange protocols • Password and biometric authentication • Anonymity and pseudonymity • Privacy • Some real-world protocols (IPSec/SSL) • Attacks on network infrastructure (routing, DNS, DDos) • Wireless security

  20. Syllabus IV • Miscellaneous • Database security • Web security • Other topics (spam, …)

  21. A High-Level Introductionto Computer Security

  22. A naïve view • Computer security is about CIA: • Confidentiality, integrity, and availability • These are important, but security is about much more…

  23. A naïve view password

  24. forgot password? In reality… • Where does security end? password

  25. One good attack • Use public records to figure out someone’s password • Or, e.g., their SSN, so can answer security question… • The problem is not (necessarily) that SSNs are public • The problem is that we “overload” SSNs, and use them for more than they were intended • Note: “the system” here is not just the computer, nor is it just the network…

  26. A naïve view • Achieve “absolute” security

  27. In reality… • Absolute security is easy to achieve! • How…? • Absolute security is impossible to achieve! • Why…? • Good security is about risk management

  28. Security as a trade-off • The goal is not (usually) “to make the system as secure as possible”… • …but instead, “to make the system as secure as possible within certain constraints” (cost, usability, convenience) • Must understand the existing constraints • E.g., passwords…

  29. Cost-benefit analysis • Important to evaluate what level of security is necessary/appropriate • Cost of mounting a particular attack vs. value of attack to an adversary • Cost of damages from an attack vs. cost of defending against the attack • Likelihood of a particular attack • Sometimes the best security is to make sure you are not the easiest target for an attacker…

  30. “More” security not always better • “No point in putting a higher post in the ground when the enemy can go around it” • Need to identify the weakest link • Security of a system is only as good as the security at its weakest point… • Security is not a “magic bullet” • Security is a process, not a product

  31. Computer security is not just about security • Detection, response, audit • How do you know when you are being attacked? • How quickly can you stop the attack? • Can you identify the attacker(s)? • Can you prevent the attack from recurring? • Recovery • Can be much more important than prevention • Economics, insurance, risk management… • Offensive techniques • Security is a process, not a product…

  32. Computer security is not just about computers • What is “the system”? • Physical security • Social engineering • Bribes for passwords • Phishing • “External” means of getting information • Legal records • Trash cans • Security is a process, not a product…(!)

  33. Security mindset • Learn to think with a “security mindset” in general • What is “the system”? • How could this system be attacked? • What is the weakest point of attack? • How could this system be defended? • What threats am I trying to address? • How effective will a given countermeasure be? • What is the trade-off between security, cost, and usability?

  34. An example: airline security • Ask: what is the cost (economic and otherwise) of current airline security? • Ask: do existing rules (e.g., banning liquids) make sense? • Ask: are the tradeoffs worth it? • (Why do we not apply the same rules to train travel?) • (Would spending money elsewhere be more effective?) • Ask: how would you get on a plane if you were on the no-fly list? • (I will not give you the answer – you can find it online) • This is a thought experiment only!

  35. Summary • “The system” is not just a computer or a network • Prevention is not the only goal • Cost-benefit analysis • Detection, response, recovery • Nevertheless…in this course, we will focus on computer security, and primarily on prevention • If you want to be a security expert, you need to keep the rest in mind

  36. Why is computer security so hard? • Computer networks are “systems of systems” • Your system may be secure, but then the surrounding environment changes • Too many things dependent on a small number of systems • Society is unwilling to trade off features for security • Ease of attacks • Cheap • Distributed, automated • Anonymous • Insider threats • Security not built in from the beginning • Humans in the loop… • Computers ubiquitous…

  37. Computers are everywhere… • …and can always be attacked • Electronic banking, social networks, e-voting • iPods, iPhones, PDAs, RFID transponders • Automobiles • Appliances, TVs • (Implantable) medical devices • Cameras, picture frames(!) • See http://www.securityfocus.com/news/11499

  38. “Trusting trust” (or: how hard is security?)

  39. “Trusting trust” • Consider a compiler that embeds a trapdoor into anything it compiles • How to catch? • Read source code? (What if replaced?) • Re-compile compiler? • What if the compiler embeds the trojan code whenever it compiles a compiler? • (That’s nasty…)

  40. “Trusting trust” • Whom do you trust? • Does one really need to be this paranoid?? • Probably not • Sometimes, yes • Shows that security is complex…and essentially impossible • Comes back to risk/benefit trade-off

  41. Next time: begin cryptography

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