CRYPTOGRAPHY & NETWOK SECURITY- Symmetric key Ciphers

CRYPTOGRAPHY & NETWOK SECURITY- Symmetric key Ciphers Dr R Jegadeesan Prof-CSE Jyothishmathi Institute of Technology and Science, karimnagar

Symmetric & Asymmetric key Ciphers Syllabus UNIT – II: Symmetric key Ciphers: Block Cipher principles, DES, AES, Blowfish, RC5, IDEA, Block cipher operation, Stream ciphers, RC4. Asymmetric key Ciphers: Principles of public key cryptosystems, RSA algorithm, Elgamal Cryptography, Diffie-Hellman Key Exchange, Knapsack Algorithm. Objective of DES 2

Symmetric & Asymmetric key Ciphers Aim & Objective : ❏ To review a short history of DES ❏ To define the basic structure of DES ❏ To describe the details of building elements of DES ❏ To describe the round keys generation process ❏ To analyze DES UNIT – II: Symmetric key Ciphers: Block Cipher principles, DES, AES, Blowfish, RC5, IDEA, Block cipher operation, Stream ciphers, RC4. Asymmetric key Ciphers: Principles of public key cryptosystems, RSA algorithm, Elgamal Cryptography, Diffie-Hellman Key Exchange, Knapsack Algorithm. Objective of DES 3

Symmetric & Asymmetric key Ciphers The Data Encryption Standard (DES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST). In 1973, NIST published a request for proposals for a national symmetric-key cryptosystem. A proposal from IBM, a modification of a project called Lucifer, was accepted as DES. DES was published in the Federal Register in March 1975 as a draft of the Federal Information Processing Standard (FIPS). Introduction & History 4

Symmetric & Asymmetric key Ciphers DES is a block cipher, as shown in Figure 6.1. Figure 6.1 Encryption and decryption with DES Overview 5

Symmetric & Asymmetric key Ciphers Figure 6.2 General structure of DES General structure of DES 6

Symmetric & Asymmetric key Ciphers Figure 6.3 Initial and final permutation steps in DES Initial and Final Permutations 7

Symmetric & Asymmetric key Ciphers DES uses 16 rounds. Each round of DES is a Feistel cipher. Round Function 8 Figure 6.4 A round in DES (encryption site)

Symmetric & Asymmetric key Ciphers The heart of DES is the DES function. The DES function applies a 48-bit key to the rightmost 32 bits to produce a 32-bit output. DES Function 9 Figure 6.5 DES function

Symmetric & Asymmetric key Ciphers Expansion P-box Since RI−1 is a 32-bit input and KI is a 48-bit key, we first need to expand RI−1 to 48 bits. Expansion P-box 10 Figure 6.6 Expansion permutation

Symmetric & Asymmetric key Ciphers Although the relationship between the input and output can be defined mathematically, DES uses Table 6.2 to define this P-box. Expansion P-box Table 11 Table 6.6 Expansion P-box table

Symmetric & Asymmetric key Ciphers S-Boxes The S-boxes do the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit output. See Figure 6.7. S-boxes 12 Figure 6.7 S-boxes

Symmetric & Asymmetric key Ciphers S-Box rule The S-boxes do the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit output. See Figure 6.7. S-box rules 13 Figure 6.8 S-box rule

Symmetric & Asymmetric key Ciphers S-Box Table 6.3 shows the permutation for S-box 1. For the rest of the boxes see the textbook. S-box Table 14

UNIT-II : Symmetric & Asymmetric key Ciphers Table 6.11 Straight permutation table Straight Permutation 15

UNIT-II : Symmetric & Asymmetric key Ciphers Figure 6.9 DES cipher and reverse cipher for the first approach DES cipher and reverse cipher approach 16

Symmetric & Asymmetric key Ciphers Figure 6.10 Key generation Key generations 17

Symmetric & Asymmetric key Ciphers Text & Reference Books 18 Book Details : TEXT BOOKS: 1. Cryptography and Network Security – Principles and Practice: William Stallings, Pearson Education, 6th Edition 2. Cryptography and Network Security: Atul Kahate, Mc Graw Hill, 3rd Edition REFERENCE BOOKS: 1. Cryptography and Network Security: C K Shyamala, N Harini, Dr T R Padmanabhan, Wiley India, 1st Edition. 2. Cryptography and Network Security : Forouzan Mukhopadhyay, Mc Graw Hill, 3rd Edition 3. Information Security, Principles, and Practice: Mark Stamp, Wiley India. 4. Principles of Computer Security: WM. Arthur Conklin, Greg White, TMH 5. Introduction to Network Security: Neal Krawetz, CENGAGE Learning 6. Network Security and Cryptography: Bernard Menezes, CENGAGE Learning

Symmetric & Asymmetric key Ciphers Video reference 19 Video Link details (NPTEL, YOUTUBE Lectures and etc.) •https://nptel.ac.in/courses/106105031/ •https://nptel.ac.in/courses/106105162/ •http://www.nptelvideos.in/2012/11/cryptography-and-network- security.html

Symmetric & Asymmetric key Ciphers Security courses 20 courses available on <www.coursera.org>, and http://neat.aicte-india.org https://www.coursera.org/ Course 1 : Introduction to Cyber Security Cyber Security. An introduction to modern information and system protection technology and methods. Course 2: Cyber security Specialization -Cyber security Fundamentals. Construction of Secure Systems

Symmetric & Asymmetric key Ciphers Security Tutorials 21 Tutorial topic wise ➢Cryptography Tutorial – Tutorialspoint www.tutorialspoint.com › cryptography ➢Cryptography Introduction – GeeksforGeeks www.geeksforgeeks.org › cryptography- introduction ➢www.cse.iitm.ac.in › ~chester › courses › slides › 01_ Introduction

Symmetric & Asymmetric key Ciphers Network Security MCQs 22 CNS – MCQs 1.Cryptography, a word with Greek origins, means a. Corrupting Data b. Secret Writing c. Open Writing d. Closed Writing 2.A transposition cipher reorders (permutes) symbols in a a. block of packets b. block of slots c. block of signals d. block of symbols 3.The cipher feedback (CFB) mode was created for those situations in which we need to send or receive r bits of a. Frames b. Pixels c. Data d. Encryption 4.In Cryptography, when text is treated at the bit level, each character is replaced by a. 4 Bits b. 6 Bits c. 8 Bits d. 10 B its a. 5.The Advanced Encryption Standard (AES) was designed a. National Institute of Standards and Technology b. IBM c. HP d. Intel

Symmetric & Asymmetric key Ciphers Security Tutorial 23 CNS –Tutorial Problems: The input to S-box 1 is 100011. What is the output? If we write the first and the sixth bits together, we get 11 in binary, which is 3 in decimal. The remaining bits are 0001 in binary, which is 1 in decimal. We look for the value in row 3, column 1, in Table 6.3 (S-box 1). The result is 12 in decimal, which in binary is 1100. So the input 100011 yields the output 1100. The input to S-box 8 is 000000. What is the output? If we write the first and the sixth bits together, we get 00 in binary, which is 0 in decimal. The remaining bits are 0000 in binary, which is 0 in decimal. We look for the value in row 0, column 0, in Table 6.10 (S-box 8). The result is 13 in decimal, which is 1101 in binary. So the input 000000 yields the output 1101.

Symmetric & Asymmetric key Ciphers CNS Questions 24 Universities & Important Questions: 1. State Euler’s Theorem, 2. Define Diffusion and Confusion. 3. Brief the strengths of Triple DES. 4. Describe meet-in-the-middle-attack 5. What are the essential steps to be taken to encrypt a data using public key cryptography. 6. What is factoring problem? 7. What is called avalanche effect? 8. Describe the use of S-Box in DES algorithm 9. What is an elliptic curve? 10. What is the role of the public key authority in key distribution system? 11. Explain possible attacks on RSA algorithm 12. State the requirements for message authentication? 13. What is message authentication?

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