EE450-U11-NetworkSecurity-Nazarian-Spring10

EE450-U11-NetworkSecurity-Nazarian-Spring10 - University...

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University of Southern California Viterbi School of Engineering EE450 omputer Networks Computer Networks etwork Security Network Security Shahin Nazarian Spring 2010
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What is Network Security? Confidentiality Confidentiality: Only sender, intended receiver should “understand” message contents Sender encrypts message Receiver decrypts message Authentication Authentication: Sender, and receiver want to confirm identity of each other ntegrity ender nd receiver ant to ensure Integrity Integrity: Sender, and receiver want to ensure message not altered (in transit, or afterwards) without detection Access and availability Access and availability: Services must be accessible and available to users Shahin Nazarian/EE450/Spring 2010 2
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Friends & Enemies: Alice, Bob, & Trudy Well-known in network security world! ob Alice (lovers!) want to communicate “securely” Bob, Alice (lovers!) want to communicate securely Trudy or Eve (intruder) may intercept, delete, add messages mg channel data, control essages Alice Bob secure sender secure eceiver messages data data rece ver Shahin Nazarian/EE450/Spring 2010 Trudy 3
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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 Shahin Nazarian/EE450/Spring 2010 4
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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 lace place Denial of service : prevent service from being used by others (e.g., by overloading resources) Shahin Nazarian/EE450/Spring 2010 5
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Message Confidentiality The The concept concept of of how how to to achieve achieve message message confidentiality or privacy has has not not changed changed for for thousands thousands of of years years The The message message must must be b ee n c r y p t e d encrypted at at the the sender sender site site and and decrypted decrypted at at the the receiver receiver ite site his can be done using either This can be done using either Symmetric Symmetric-key cryptography key cryptography or symmetric ey cryptography Shahin Nazarian/EE450/Spring 2010 Asymmetric Asymmetric-key cryptography key cryptography 6
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The Language of Cryptography K A Alice’s encryption key Bob’s decryption key K B plaintext plaintext ciphertext encryption algorithm decryption algorithm Eve Symmetric key crypto.: sender and receiver keys are identical and secret symmetric ublic- ey rypto : ncryption key is however Asymmetric ( public key ) crypto.: encryption key is public, however the decryption key is secret (private) Knowing the public key, Eve should not be able to calculate the private key Shahin Nazarian/EE450/Spring 2010 7
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Comparison between Two Categories of Cryptography Shahin Nazarian/EE450/Spring 2010
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Message Confidentiality Using Symmetric Keys in Two Directions Shahin Nazarian/EE450/Spring 2010 9
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Symmetric Key Cryptography (Cont.)
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EE450-U11-NetworkSecurity-Nazarian-Spring10 - University...

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