Advanced Computer Networks: Lecture 40 - Dr. Amir Qayyum

Advanced Computer Networks: Lecture 40. This lecture will cover the following: security; encryption algorithms; cryptography functions; taxonomy of network security; secret key encryption; public key authentication; authentication protocols; message integrity protocols; key distribution; firewalls;...

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CS716 Advanced Computer Networks

By Dr. Amir Qayyum

Lecture No. 40 

– Integrity: making sure message has not been 

altered 

Taxonomy of Network Security

Security

Cryptography algorithms

Public key (e.g RSA)

Secret

key

(e.g DES)

Message digest (e.g MD5)

Security services

Authentication

integrity

Secret Key Encryption

Final permutation

Expansion Phase of DES

4-bit chunk

Expanded to 6 bits by stealing

a bit from left and right chunks

■ ■ ■

■ ■ ■

• Repeat for larger messages 

Cipher Block Chaining (CBC)

Block 1 IV

+ +

+

Public Key Encryption

Public Key Authentication

Plaintext Decrypt with private key

– Two numbers are relatively prime if they have no common factor greater than one

Message Digest

– Just as a regular checksum protects the receiver from accidental changes to the message, a cryptographic checksum 

protects the receiver from malicious 

changes to the message

Message Integrity

• Applies MD5 to the concatenation of this  random key message

Tree­structured CA Hierarchy

Authentication

Session Key Communication

Session Key Communication

Key 

Distribution 

Center