Network Security

Section 1: Introduction to security

What is Security?

• What is the biggest enemy for humans?H U M A N S!

• We need security until the people with bad minds exists!

• What is the best solution for security?

No high-tech hardware

No high-tech software

Change the way of thinking!

SIMPLEBUT

HARD TO DO!

Why security?

• Why Linux is more secure than Windows?

Popularity of Windows

• Why Firefox is more secure that IE?

Popularity of IE

• Why network security is not important in IRAN?

Unpopularity of information in computers

What is Network Security?

C I A

Confidentiality

Integrity Availability

People with bad minds

Network Security Problems

• Secrecy

• Authentication

• Non-repudiation

• Integrity Control

Physical vs. Network Security

• Security in real word– Voice, Face, Handwritting

• Security in Network– Cryptography, Digital Signature

Cryptography

• Cryptography Lexicon

• Cipher vs. Code

• Plaintext, Key, Cipher text

• Crypto analysis

• Cryptology

• Work Factor

C = Ek(P) & P = Dk(C)

• C: Cipher text, K: Key, P: Plaintext

• E: Encryption Function

• D: Decryption Function

• Dk(Ek(P)) = ?

• Main Rule for Cryptography: Algorithm must be clear for all only key is hidden.

• Security by obscurity

Crack Cipher text

• Problems:– Cipher text Only– Known Plaintext– Chosen Plaintext

• Cipher text only– Do you think it’s not crack able?

Yes!

No, What is your idea?

Substitution Cipher

• One or group of character(s) substitute with another character.

• A => D, B => E, C => F.

• Attack => DWWDFN

• kths character substitution.

• What is your idea for cracking it?– Estimating usual character, Estimating usual

word

Transposition Cipher

• Change the situation/ Transpose of characters.

Any idea for cracking this kind of encryption?

One-Time Pads

• Use random key.

• Not crack able at all! Because of information theory.

• Example: I LOVE YOU! What are the problems?

Long padsHard to transportation