chapter-6 - CS549 Cryptography and Network Security by...

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Cryptography and Network Security 1 CS549: Cryptography and Network Security © by Xiang-Yang Li Department of Computer Science, IIT
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Cryptography and Network Security 2 Notice© This lecture note (Cryptography and Network Security) is prepared by Xiang-Yang Li. This lecture note has benefited from numerous textbooks and online materials. Especially the “Cryptography and Network Security” 2 nd edition by William Stallings and the “Cryptography: Theory and Practice” by Douglas Stinson. You may not modify, publish, or sell, reproduce, create derivative works from, distribute, perform, display, or in any way exploit any of the content, in whole or in part, except as otherwise expressly permitted by the author. The author has used his best efforts in preparing this lecture note. The author makes no warranty of any kind, expressed or implied, with regard to the programs, protocols contained in this lecture note. The author shall not be liable in any event for incidental or consequential damages in connection with, or arising out of, the furnishing, performance, or use of these.
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Cryptography and Network Security 3 Cryptography and Network Security Authentication Xiang-Yang Li
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Cryptography and Network Security 4 Message Authentication Digital Signature Authentication Authentication requirements Authentication functions Mechanisms MAC: message authentication code Hash functions, security in hash functions Hash and MAC algorithms MD5, SHA, RIPEMD-160, HMAC Digital signatures
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Cryptography and Network Security 5 Message Attacks Possible attacks Disclosure Traffic analysis Masquerade Content modification Sequence modification Time modification Repudiation Denial of the receipt of message by the destination or Denial of the transmitting by the source
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Cryptography and Network Security 6 Authentication Enables receiver to verify message authenticity Using some lower level functions as primitive Three types of functions Message encryption Message authentication code (MAC) Hash function
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Cryptography and Network Security 7 Authentication Goal: Bob wants Alice to “prove” her identity to him Protocol ap1.0: Alice says “I am Alice” Failure scenario?? I am Alice”
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Cryptography and Network Security 8 Authentication Goal: Bob wants Alice to “prove” her identity to him Protocol ap1.0: Alice says “I am Alice” in a network, Bob can not “see” Alice, so Trudy simply declares herself to be Alice I am Alice”
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Cryptography and Network Security 9 Authentication: another try Protocol ap2.0: Alice says “I am Alice” in an IP packet containing her source IP address Failure scenario?? I am Alice” Alice’s IP address
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Cryptography and Network Security 10 Authentication: another try Protocol ap2.0: Alice says “I am Alice” in an IP packet containing her source IP address Trudy can create a packet “spoofing” Alice’s address I am Alice” Alice’s IP address
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