1. Network Security Section 1: Introduction to security

2. 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! SIMPLE BUT HARD TO DO!

3. 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

4. What is Network Security? C I A Confidentiality Integrity Availability

5. People with bad minds

6. Network Security Problems Secrecy Authentication Non-repudiation Integrity Control

7. Physical vs. Network Security Security in real word –Voice, Face, Handwritting Security in Network –Cryptography, Digital Signature

8. Cryptography Cryptography Lexicon Cipher vs. Code Plaintext, Key, Cipher text Crypto analysis Cryptology Work Factor

9. 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

10. 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?

11. 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

12. Transposition Cipher Change the situation/ Transpose of characters. Any idea for cracking this kind of encryption?

13. One-Time Pads Use random key. Not crack able at all! Because of information theory. Example: I LOVE YOU! What are the problems? Long pads Hard to transportation