EE450-U11-NetworkSecurity_Lecture-Nazarian-Summer10

EE450-U11-NetworkSecurity_Lecture-Nazarian-Summer10 - EE450...

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EE450 Computer Networks Network Security Shahin Nazarian Summer 2010
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Shahin Nazarian/EE450/Summer 2010 What is Network Security? 2
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Shahin Nazarian/EE450/Summer 2010 Friends & Enemies: Alice, Bob, & Trudy Well-known in network security world! Bob, Alice (lovers!) want to communicate “securely” Trudy or Eve (intruder) may intercept, delete, add messages secure sender secure receiver channel data, control messages data data Alice Bob Trudy 3
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Shahin Nazarian/EE450/Summer 2010 Who Might Bob and 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 4
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Shahin Nazarian/EE450/Summer 2010 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) 5
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Shahin Nazarian/EE450/Summer 2010 Message Confidentiality 6
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Shahin Nazarian/EE450/Summer 2010 The Language of Cryptography plaintext plaintext ciphertext K A encryption algorithm decryption algorithm Alice’s encryption key Bob’s decryption key K B 7 Symmetric key crypto.: sender and receiver keys are identical and secret Asymmetric ( _____-key ) crypto.: encryption key is public , however the decryption key is ( private) Knowing the public key, Eve should not be able to calculate the private key Eve
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Shahin Nazarian/EE450/Summer 2010 Comparison between Two Categories of Cryptography
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Shahin Nazarian/EE450/Summer 2010 Message Confidentiality Using Symmetric Keys in Two Directions 9
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Shahin Nazarian/EE450/Summer 2010 Symmetric Key Cryptography (Cont.) Symmetric key crypto: Bob and Alice share know same (symmetric) key: K A-B E.g., key is knowing substitution pattern in mono alphabetic substitution cipher plaintext ciphertext K A-B encryption algorithm decryption algorithm K A-B plaintext message, m K (m) A-B K (m) A-B m = K ( ) A-B
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Shahin Nazarian/EE450/Summer 2010 Symmetric Key Cryptography – Example Substitution cipher: Substituting one thing for another Monoalphabetic cipher: substitute one letter for another Plaintext: abcdefghijklmnopqrstuvwxyz Ciphertext: mnbvcxzasdfghjklpoiuytrewq Plaintext: bob. i love you. alice Ciphertext: nkn. s gktc wky. mgsbc E.g.: Q: How hard to break this simple cipher?
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EE450-U11-NetworkSecurity_Lecture-Nazarian-Summer10 - EE450...

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