Encryption can be a difficult issue to comprehend, inside of PHP or not. Thankfully, there are resources out there that can help simplify things and bring them down to where they're really useful. This new tutorial from the IBM developerWorks site today is just such a resource.
In this increasingly virtual online world, you have to be careful to protect your data. Learn the basics of encoding and encrypting important bits of information, such as passwords, credit card numbers, and even entire messages. Get an overview of what it means to encrypt and decrypt information, as well as some practical examples involving passwords and other data, using PHP's built-in functionality.
They start off where any good encryption article should - with a primer in cyrptography. You can't understand the advanced without a good grasp on the basic. Using this knowledge, they start to work up their form, a simple username and password validation system.
They provide all of the code you'll need to build the form, and even intorduce you to the crypt() function. A bad use of this functionality is also illustrated. Of course, encryption is only half the fun, so they also include an example of decrypting the same information.