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lecture15 - 1 EEC-484/584 Computer Networks Lecture 15...

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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]
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2 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
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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 3Wenbing Zhao
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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
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5 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
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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
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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)
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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
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9 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 Encryption can also be used to ensure integrity (i.e., unauthorized change can be detected) Encryption is the basis of protocols that enable us to provide security while accomplishing system or network tasks
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