cmsc 414 computer and network security lecture 27.ppt

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cmsc 414 computer and network security lecture 27.ppt

CMSC 414 Computer and Network Security Lecture 27 Jonathan Katz Course evaluation http://www.CourseEvalUM. Final exam Exam will be comprehensive Questions similar in style to the midterm Besides understanding each topic in isolation, try to see the connections and relationships I will post a summary of topics you need to know Network layers Application Transport Network Data link Physical Roughly… Application layer: the communicating processes themselves and the actual ‘content’ transmitted Transport layer (TCP/UDP): handles transmissions on an “end-to-end” basis; Network layer (IP): handles transmissions on a “hop-by-hop” basis; routing Data link layer (Ethernet/WiFi): transmission of frames over a single hop Example security protocols Application layer: PGP Transport layer: SSL/TLS Network layer: IPsec Data link layer: IEEE 802.11 Security at the physical layer? Security in what layer? Depends on the purpose… What information needs to be protected? What is the attack model? Who shares keys in advance? Should the user be involved? E.g., a network-layer protocol cannot authenticate two end-users to each other An application-layer protocol cannot protect IP header information Also affects efficiency, ease of deployment, etc. Generally… When security is placed as lower levels, it can provide automatic, “blanket” coverage… …but it can take a long time before it is widely adopted When security is placed at higher levels, individual users can choose when to use it… …but users who are not security-conscious may not take advantage of it Note… The “best” solution is not necessarily to use PGP over IPsec! Would have been better to design the Internet with security in mind from the beginning… Example: PGP vs. SSL vs. IPsec PGP is an application-level protocol for “secure email” Can provide security on “insecure” systems Users choose when to use PGP; user must be involved Alice’s signature on an email proves that Alice actually generated the message, and it was received u

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