This document discusses cryptography and contains sections on symmetric-key cryptography, public-key cryptography, and security protocols on the internet. It includes diagrams of encryption algorithms like DES and RSA, as well as block ciphers, product blocks, substitution ciphers, and encryption modes like ECB and CBC. Key points covered include how symmetric-key cryptography uses the same key for encryption and decryption while public-key uses different keys, and how algorithms like DES are more complex versions of the Caesar cipher.

1. Security PART VII

2. Security Topics

3. Chapters Chapter 29 Cryptography Chapter 30 Message Authentication, User Authentication, and Key Management Chapter 31 Security Protocols in The Internet

4. Chapter 29 Cryptography

5. 29.1 Introduction Introduction to Cryptography

6. Figure 29.1 Cryptography components

7. Figure 29.2 Encryption and decryption

8. In cryptography, the encryption/decryption algorithms are public; the keys are secret. Note :

9. 29.2 Symmetric-Key Cryptography Traditional Cipher Block Cipher Operation Modes

10. Figure 29.3 Symmetric-key cryptography

11. In symmetric-key cryptography, the same key is used by the sender (for encryption) and the receiver (for decryption). The key is shared. Note :

12. In symmetric-key cryptography, the same key is used in both directions. Note :

13. Symmetric-key cryptography is often used for long messages. Note :

14. Figure 29.4 Caesar cipher

15. Figure 29.5 Example of monoalphabetic substitution

16. In monoalphabetic substitution, the relationship between a character in the plaintext to the character in the ciphertext is always one-to-one. Note :

17. Figure 29.6 Vigenere cipher

18. In polyalphabetic substitution, the relationship between a character in the plaintext and a character in the ciphertext is one-to-many. Note :

19. Figure 29.7 Transpositional cipher

20. Figure 29.8 Block cipher

21. Figure 29.9 P-box

22. Figure 29.10 S-box

23. Figure 29.11 Product block

24. Figure 29.12 DES

25. Figure 29.13 General scheme of DES

26. Figure 29.14 Iteration block

27. Figure 29.15 Triple DES

28. The DES cipher uses the same concept as the Caesar cipher, but the encryption/decryption algorithm is much more complex due to the sixteen 48-bit keys derived from a 56-bit key. Note :

29. Figure 29.16 ECB mode

30. Figure 29.17 CBC mode

31. Figure 29.18 CFM

32. Figure 29.19 CSM

33. 29.3 Public-Key Cryptography RSA Choosing Public and Private Keys

34. Figure 29.20 Public-key cryptography

35. Public-key algorithms are more efficient for short messages. Note :

36. Figure 29.21 RSA