tailieunhanh - Lecture Network security: Chapter 14 - Dr. Munam Ali Shah

This chapter includes contents: We will explore block ciphers and stream ciphers with some examples, second dimension of the cryptography, what is fesitel structure and why is it used will also be part of today’s lecture, importantly, we will discuss data encryption standard (DES). | Network Security Lecture 14 Presented by: Dr. Munam Ali Shah Summary of the previous lecture We discussed another technique of Substitution Cipher, ., Vigenere Cipher in which we have key and plain text of same size. We use rows and columns and create cipher text We also discussed OTP and have seen that the security is unbreakable but it is impractical because Generating large quantities of random keys is an issue Key cannot be repeated Distribution of keys is an even bigger issue Lastly, we discussed Transposition Cipher and two techniques, ., Rail Fence Cipher and Row Cipher with examples were discussed . Part 2 (c) Symmetric Key Cryptography Outlines of today’s lecture We will explore block ciphers and stream ciphers with some examples. Second dimension of the cryptography What is Fesitel Structure and why is it used will also be part of today’s lecture Importantly, we will discuss Data Encryption Standard (DES) Objectives You would be able to present an understanding of . | Network Security Lecture 14 Presented by: Dr. Munam Ali Shah Summary of the previous lecture We discussed another technique of Substitution Cipher, ., Vigenere Cipher in which we have key and plain text of same size. We use rows and columns and create cipher text We also discussed OTP and have seen that the security is unbreakable but it is impractical because Generating large quantities of random keys is an issue Key cannot be repeated Distribution of keys is an even bigger issue Lastly, we discussed Transposition Cipher and two techniques, ., Rail Fence Cipher and Row Cipher with examples were discussed . Part 2 (c) Symmetric Key Cryptography Outlines of today’s lecture We will explore block ciphers and stream ciphers with some examples. Second dimension of the cryptography What is Fesitel Structure and why is it used will also be part of today’s lecture Importantly, we will discuss Data Encryption Standard (DES) Objectives You would be able to present an understanding of Symmetric Key Cryptography. You would be able use understand the phases involved in DES. Symmetric Key Cryptography Symmetric key Encryption and Decryption keys are the same, or Decryption key can be easily calculated from encryption key Examples: Classical ciphers DES AES Also called, Classical Encryption, Private key cryptography, single key cryptography Symmetric Key Cryptography 8 Symmetric Key Cryptography Mathematically, we represent encryption process by C = EK(P) or C = E(K,P) and decryption process by P = DK(C) or P = D(K,C) where P: Plaintext, C: Ciphertext, K:Symmetric key, E: Encryption algorithm, D: Decryption algorithm Block Ciphers The most widely used block cipher is Data Encryption Standard (DES) Structure of symmetric block ciphers is very complex as compared to asymmetric ciphers Stream Vs Block Ciphers A stream cipher is one that encrypts a digital data stream one bit or one byte at a time. Examples are Vernam cipher; RC-4; SEAL A block cipher is one in which a block of

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• Network security
• Lecture Network security
• Computer network
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• Internet security
• Symmetric Key Cryptographic Algorithm
• Symmetric Key Cryptosystems
• One Time Pad Algorithm
• OTP Cipher
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• Perfect encryption
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• Public key cryptosystems
• Knapsack cryptosystem
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• Block cipher
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• Discrete logarithm problem on elliptic curves
• Traditional Symmetric Key Ciphers
• Kerckhoff’s Principle
• Polyalphabetic Ciphers
• Monoalphabetic Ciphers
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• Modern block cipher
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• Physical layer
• Data link layer
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