On the PerishablePress.com site there's a recent article showing you how to encode your PHP project's code (though some of the methods are more obfuscation than actual encryption).

There are many ways to encode and decode PHP code. From the perspective of site security, there are three PHP functions - str_rot13(), base64_encode(), and gzinflate - that are frequently used to obfuscate malicious strings of PHP code. For those involved in the securing of websites, understanding how these functions are used to encode and decode encrypted chunks of PHP data is critical to accurate monitoring and expedient attack recovery.

They show examples of several methods of encoding/obfuscation of the code including rot13, base64, gzinflate/gzdeflate and links to some other resources.

A new post on CodeForest.net today gives you a technique for obfuscating email addresses with a combination of PHP, CSS and Javascript. It uses ROT13 for the obfuscation and some tricky CSS to keep it usable for the human visitors.

According to Wikipedia, more than 97% of all e-mails sent over the net are unwanted. That’s around 200 billion spam messages per day. To keep this insane amount of spam out of your inbox, you should keep your e-mail safe when you display it on web. One of the ways to keep it safe is to obfuscate it. In this tutorial I’ll show you how to create a script that will do just that.

The script converts the email address into a ROT13 obfuscated versions and reverse it. The spam bots harvesting addresses won't see it as a valid format but the user, thanks to some CSS rules, will see it and be able to copy it easily. Each part of the script is explained in the post and you can see a demo of it in action here.