1. TCP/IP Protocol Suite 1 Chapter 28 Upon completion you will be able to: Security Differentiate between two categories of cryptography schemes Understand four aspects of security Know how and where IPSec, TLS, and PGP provide security Firewall Objectives

2. TCP/IP Protocol Suite 2 28.1 CRYPTOGRAPHY The word cryptography in Greek means “secret writing.” The term today refers to the science and art of transforming messages to make them secure and immune to attacks. The topics discussed in this section include: Symmetric-Key Cryptography Asymmetric-Key Cryptography Comparison

3. TCP/IP Protocol Suite 3 Figure 28.1 Cryptography components

4. TCP/IP Protocol Suite 4 In cryptography, the encryption/decryption algorithms are public; the keys are secret. Note:

5. TCP/IP Protocol Suite 5 In symmetric-key cryptography, the same key is used by the sender (for encryption) and the receiver (for decryption). The key is shared. Note:

6. TCP/IP Protocol Suite 6 Figure 28.2 Symmetric-key cryptography

7. TCP/IP Protocol Suite 7 In symmetric-key cryptography, the same key is used in both directions. Note:

8. TCP/IP Protocol Suite 8 Figure 28.3 Caesar cipher

9. TCP/IP Protocol Suite 9 Figure 28.4 Transpositional cipher

10. TCP/IP Protocol Suite 10 Figure 28.5 Data Encryption Standard (DES)

11. TCP/IP Protocol Suite 11 Figure 28.6 Iteration block

12. TCP/IP Protocol Suite 12 Figure 28.7 Triple DES

13. TCP/IP Protocol Suite 13 The DES cipher uses the same concept as the Caesar cipher, but the encryption/ decryption algorithm is much more complex. Note:

14. TCP/IP Protocol Suite 14 Figure 28.8 Public-key cryptography

15. TCP/IP Protocol Suite 15 Figure 28.9 RSA

16. TCP/IP Protocol Suite 16 Symmetric-key cryptography is often used for long messages. Note:

17. TCP/IP Protocol Suite 17 Asymmetric-key algorithms are more efficient for short messages. Note:

18. TCP/IP Protocol Suite 18 28.6 SECURITY IN THE INTERNET IP Level Security: IPSec Transport Layer Security Application Layer Security: PGP

19. TCP/IP Protocol Suite 19 Figure 28.27 Transport mode

20. TCP/IP Protocol Suite 20 Figure 28.28 Tunnel mode

21. TCP/IP Protocol Suite 21 Figure 28.29 Authentication Header (AH)

22. TCP/IP Protocol Suite 22 The AH protocol provides message authentication and integrity, but not privacy. Note:

23. TCP/IP Protocol Suite 23 Figure 28.30 Encapsulating Security Payload (ESP)

24. TCP/IP Protocol Suite 24 ESP provides message authentication, integrity, and privacy. Note:

25. TCP/IP Protocol Suite 25 Figure 28.31 Position of TLS

26. TCP/IP Protocol Suite 26 Figure 28.35 PGP at the sender site

27. TCP/IP Protocol Suite 27 Figure 28.36 PGP at the receiver site

28. TCP/IP Protocol Suite 28 28.7 FIREWALLS A firewall is a device (usually a router or a computer) installed between the internal network of an organization and the rest of the Internet. It is designed to forward some packets and filter (not forward) others. A firewall is a device (usually a router or a computer) installed between the internal network of an organization and the rest of the Internet. It is designed to forward some packets and filter (not forward) others. The topics discussed in this section include: Packet-Filter Firewall Proxy Firewall

29. TCP/IP Protocol Suite 29 Figure 28.37 Firewall

30. TCP/IP Protocol Suite 30 Figure 28.38 Packet-filter firewall

31. TCP/IP Protocol Suite 31 A packet-filter firewall filters at the network or transport layer. Note:

32. TCP/IP Protocol Suite 32 Figure 28.39 Proxy firewall

33. TCP/IP Protocol Suite 33 A proxy firewall filters at the application layer. Note: