In This Chapter

• Pros and cons of data encryption

• Single key encryption

• Two-key encryption

• Combining single and two-key encryption

• Message integrity

• Digital certificates

• PKI

12.0 Introduction

Encryption is a method of changing a message so that its content isn t intelligible to a casual viewer. Using something that only the sender and receiver know, the message is turned from readable to nonsense before it is sent and restored to readable form when it is received. Encryption is the primary technique for protecting the content of a data communications message while it is traveling outside the local network on which it originated. Encryption can also be used to protect data stored on a hard disk.

In this chapter we ll begin by looking and the pros and cons of encryption and then turn to encryption methods. We ll also look at techniques that aren t precisely encryption, but ensure message integrity (ensure that a message hasn t been modified during transmission) and at techniques for ensuring message authenticity (that a message actually came from the source from which it appears to have come). Finally, we ll look at public key infrastructure (PKI), the technology resources needed to manage an encryption program.

12.1 To Encrypt or Not to Encrypt

Right now, encryption is the best technique we have for ensuring the privacy of a message when it is outside our local network. However, it s not a perfect answer:

• Encrypting and decrypting messages consumes a lot of computing power, slowing...