9 - Lecture #9 SS G513 Network Security Cryptography and...

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Lecture #9 SS G513 Network Security
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Cryptography and Network Security Third Edition by William Stallings Lecture slides by Lawrie Brown
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Chapter 11 – Message Authentication and Hash Functions At cats' green on the Sunday he took the message from the inside of the pillar and added Peter Moran's name to the two names already printed there in the "Brontosaur" code. The message now read: “Leviathan to Dragon: Martin Hillman, Trevor Allan, Peter Moran: observe and tail.” What was the good of it John hardly knew. He felt better, he felt that at last he had made an attack on Peter Moran instead of waiting passively and effecting no retaliation. Besides, what was the use of being in possession of the key to the codes if he never took advantage of it? Talking to Strange Men, Ruth Rendell
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Message Authentication message authentication is concerned with: protecting the integrity of a message validating identity of originator non-repudiation of origin (dispute resolution) will consider the security requirements then three alternative functions used: message encryption message authentication code (MAC) hash function
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Security Requirements disclosure traffic analysis masquerade content modification sequence modification timing modification source repudiation destination repudiation
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Message Encryption message encryption by itself also provides a measure of authentication if symmetric encryption is used then: receiver know sender must have created it since only sender and receiver now key used know content cannot of been altered if message has suitable structure, redundancy or a checksum to detect any changes
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Message Encryption if public-key encryption is used: encryption provides no confidence of sender since anyone potentially knows public-key however if sender signs message using their private-key then encrypts with recipients public key have both secrecy and authentication again need to recognize corrupted messages but at cost of two public-key uses on message
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Message Authentication Code (MAC) generated by an algorithm that creates a small fixed-sized block depending on both message and some key like encryption though need not be reversible appended to message as a signature receiver performs same computation on message and checks it matches the MAC provides assurance that message is unaltered and comes from sender
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Message Authentication Code
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Message Authentication Codes as shown the MAC provides confidentiality can also use encryption for secrecy generally use separate keys for each can compute MAC either before or after encryption is generally regarded as better done before why use a MAC? sometimes only authentication is needed
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This note was uploaded on 03/14/2010 for the course CSE SS ZG513 taught by Professor Sundarb during the Summer '10 term at Birla Institute of Technology & Science.

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9 - Lecture #9 SS G513 Network Security Cryptography and...

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