Computer Networking: Internet Protocols in Action

Chapter 6.1. Encryption

INTRODUCTION

The exercises in this book clearly demonstrate the kinds of information that malicious individuals can learn by sniffing traffic on a local network. Many protocols send both private data and passwords in clear text. One of the best ways to protect your privacy and the security of your systems is to replace applications that use plain text protocols like telnet and FTP with applications that encrypt data in transit. Encryption takes a plain text message and translates it into unreadable cipher text. The cipher text can only be decrypted or translated back into the original plain text message with a secret key.

There are two major types of cryptographic algorithms used to encrypt data—symmetric key cryptography and asymmetric key cryptography.

In symmetric key cryptography, both parties that are communicating must share a single secret key. If they establish this shared key in private, then they can use this shared secret to securely transmit over the network. The sending party encrypts the data using the agreed upon key and the receiver decrypts the data by reversing the encryption process. If a malicious third party were to learn the shared key, then they too could decrypt the data. Therefore, it is difficult to agree upon the shared secret key when all communication including key exchange takes place over the network.

In asymmetric key cryptography, communicating entities do not share a single secret key. Instead, each party generates a set of two ...