Chapter 12. Data Encryption

IN THIS CHAPTER

• Shared Secret Versus Public Key

• Shared Secret Algorithms

• Public Key Cryptography

• Using Public Keys in PHP

Unless you've been living under a rock for the past 10 years, you've probably heard the term cryptography (or data encryption) at least once. You've probably also got a pretty good notion of what it is: taking some piece of information and jumbling it up so that no one can read it except the people who should be able to. What you may not know is how it works and, more importantly, how you can use it in your own programs.

This chapter will cover two basic categories of encryption: shared secret and public key. Each form of encryption shares the same basic concepts: Party A uses a key and/or algorithm to transform a plain-text message into ciphertext and sends it to Party B. Party B then uses a key and/or algorithm to transform that ciphertext back into plain text.