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Network Security
Section 1: Introduction to security
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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!
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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
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What is Network Security?
C I A
Confidentiality
Integrity Availability
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People with bad minds
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Network Security Problems
• Secrecy
• Authentication
• Non-repudiation
• Integrity Control
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Physical vs. Network Security
• Security in real word– Voice, Face, Handwritting
• Security in Network– Cryptography, Digital Signature
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Cryptography
• Cryptography Lexicon
• Cipher vs. Code
• Plaintext, Key, Cipher text
• Crypto analysis
• Cryptology
• Work Factor
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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
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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?
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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
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Transposition Cipher
• Change the situation/ Transpose of characters.
Any idea for cracking this kind of encryption?
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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