Firewalls and Internet Security: Repelling the Wily Hacker, Second Edition

Chapter 18. Secure Communications over Insecure Networks

It is sometimes necessary to communicate over insecure links without exposing one’s systems. Cryptography—the art of secret writing—is the usual answer.

The most common use of cryptography is, of course, secrecy. A suitably encrypted packet is incomprehensible to attackers. In the context of the Internet, and in particular when protecting wide-area communications, secrecy is often secondary. Instead, we are often interested in authentication provided by cryptographic techniques. That is, we wish to utilize mechanisms that will prevent an attacker from forging messages.

This chapter concentrates on how to use cryptography for practical network security. It assumes some knowledge of modern cryptography. ...