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Lecture No. 41
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Message Integrity Protocols-Advance Computer Networking-Lecture Slides, Slides of Computer Networks
This course is about introduction to network programming. Topics covered in this are direct link networks, packet switching, internetworking, end-to-end protocols, congestion control and resource, allocation, end-to-end data, applications. This lecture includes: Message, Integrity, Protocols, Digital, Signatures, Public, Private, Key, Decrypt, Checksum, Authentication, Session
Typology: Slides
2011/2012
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Lecture No. 41
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Message Integrity Protocols
- Digital signature using RSA
- Special case of a message integrity where
the code can only have been generated byone participant
- Compute signature with private key and
verify with public key
5
Message Integrity Protocols
- MD5 with RSA signature
- Sender:
m
+ E(MD5(
m
private
- Receiver
- Decrypts signature with sender’s
public key
- Compares result with MD5 checksum
sent with message
6
Authentication
8
Session Key Communication
9
Key
Distribution
Center
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Man-in-the-Middle Attack
in Diffie-Hellman
12
Key Distribution
- Certificate
- Special type of digitally signed document:
“I certify that the public key in this document
belongs to the entity named in this document,signed X.”
- The name of the entity being certified– The public key of the entity– The name of the certification authority– A digital signature
14
Tree-structured CA Hierarchy
15
Key Distribution (cont)
- Chain of Trust
- If
X
certifies that a certain public key
belongs to
Y
, and
Y
certifies that another
public key belongs to
Z
, then there exists
a chain of certificates from
X
to
Z
- Someone that wants to verify
Z
’s public
key has to know
X
’s public key and
follow the chain
- Certificate Revocation List
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PGP Message Encryption
Decrypt message usingDES with secret key
k
Decrypt E(
k ) using RSA with
my private key
k
Convert ASCII message
Encrypt
k
using RSA with
recipient s public key Encode message + E(
k )
Encrypt message using in ASCII for transmission DES with secret key
k
Original message
Transmitted message
Create a random secret key
k
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Example (PGP)
20
Secure Transport Layer
Application (e.g. HTTP)
Secure transport layer
TCP
IP Subnet
21
TLS Handshake Protocol
Client
Server