Chapter 16. IP Security

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16.1 IP Security Overview

16.2 IP Security Architecture

16.3 Authentication Header

16.4 Encapsulating Security Payload

16.5 Combining Security Associations

16.6 Key Management

16.7 Recommended Reading and Web Sites

16.8 Key Terms, Review Questions, and Problems

Appendix 16A Internetworking and Internet Protocols

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If a secret piece of news is divulged by a spy before the time is ripe, he must be put to death, together with the man to whom the secret was told.

The Art of War, Sun Tzu

Key Points

• IP security (IPSec) is a capability that can be added to either current version of the Internet Protocol (IPv4 or IPv6), by means of additional headers.

• IPSec encompasses three functional areas: authentication, confidentiality, and key management.

• Authentication makes use of the HMAC message authentication code. Authentication can be applied to the entire original IP packet (tunnel mode) or to all of the packet except for the IP header (transport mode).

• Confidentiality is provided by an encryption format known as encapsulating security payload. Both tunnel and transport modes can be accommodated.

• IPSec defines a number of techniques for key management.

The Internet community has developed application-specific security mechanisms in a number of application areas, including electronic mail (S/MIME, PGP), client/server (Kerberos), Web access (Secure Sockets Layer), and others. However, users have some security concerns that cut across protocol layers. For example, an enterprise can run a secure, private TCP/IP network by disallowing links to untrusted sites, encrypting packets that leave the premises, and authenticating packets that enter the premises. By implementing security at the IP level, an organization can ensure secure networking not only for applications that have security mechanisms but also for the many security-ignorant applications.

IP-level security encompasses three functional areas: authentication, confidentiality, and key management. The authentication mechanism assures that a received packet was, in fact, transmitted by the party identified as the source in the packet header. In addition, this mechanism assures that the packet has not been altered in transit. The confidentiality facility enables communicating nodes to encrypt messages to prevent eavesdropping by third parties. The key management facility is concerned with the secure exchange of keys.

We begin this chapter with an overview of IP security (IPSec) and an introduction to the IPSec architecture. We then look at each of the three functional areas in detail. The appendix to this chapter reviews internet protocols.