lecture15 - 1 Click to edit Master subtitle style Spring...

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Unformatted text preview: 1 Click to edit Master subtitle style Spring Semester 2009 EEC-484/584: Computer Networks EEC-484/584 Computer Networks Lecture 15 Wenbing Zhao [email protected] 2 Spring Semester 2009 EEC-484/584: Computer Networks Spring Semester 2009 EEC-484/584: Computer Networks 2Wenbing Zhao Outline • Reminder: – Wiki page peer review due tonight (5/4) • Quiz#4 result • Introduction to network security and cryptography 3 Spring Semester 2009 EEC-484/584: Computer Networks Quiz#4 Result • High 100, low 63, mean 88.5 • Q1 45.4/50, Q2 8.6/10, Q3 10/10, Q4 9.1/10, Q5 15.4/20 Spring Semester 2009 EEC-484/584: Computer Networks 3Wenbing Zhao 4 Spring Semester 2009 EEC-484/584: Computer Networks 8: Network Security 48-4 What is network security? Confidentiality: only sender, intended receiver should “understand” message contents – sender encrypts message – receiver decrypts message Authentication: sender, receiver want to confirm identity of each other Message integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection Access and availability: services must be accessible and available to users 5 8: Network Security 8: Network Security 58-5 Friends and enemies: Alice, Bob, Trudy • Well-known in network security world • Bob, Alice want to communicate “securely” • Trudy (intruder) may intercept, delete, add messages secure sender secure receiver channel data, control messages data data Alice Bob Trudy 6 Spring Semester 2009 EEC-484/584: Computer Networks 8: Network Security 68-6 Who might Bob, Alice be? • … well, real-life Bobs and Alices! • Web browser/server for electronic transactions (e.g., on-line purchases) • On-line banking client/server • DNS servers • Routers exchanging routing table updates 7 Spring Semester 2009 EEC-484/584: Computer Networks 8: Network Security 78-7 There are bad guys (and girls) out there! Q: What can a “bad guy” do? A: A lot! – Eavesdrop: intercept messages – Actively insert messages into connection – Impersonation: can fake (spoof) source address in packet (or any field in packet) – Hijacking: “take over” ongoing connection by removing sender or receiver, inserting himself in place – Denial of service : prevent service from being used by others (e.g., by overloading resources) 8 Spring Semester 2009 EEC-484/584: Computer Networks 8: Network Security 88-8 The Language of Cryptography plaintext plaintext ciphertext K A encryption algorithm decryption algorithm Alice’s encryption key Bob’s decryption key K B • Plaintext : message to be encrypted • Ciphertext : encrypted message • DK(EK(P)) = P 9 Spring Semester 2009 EEC-484/584: Computer Networks Spring Semester 2009 EEC-484/584: Computer Networks 9Wenbing Zhao Cryptography Terminology • Encryption is the process of encoding a message so that its meaning is not obvious – Equivalent terms: encode , encipher • Encryption addresses the need for confidentiality of data •...
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lecture15 - 1 Click to edit Master subtitle style Spring...

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