On PHPBuilder.com today, there's a new tutorial that talks about a method to securing data sent via GET requests in your application.

In this article I'm going to show you how you can use PHP to encode your data for transit. Most importantly, it will be done in a way that makes the data decodable, and therefore much more usable, by the receiving page.

They talk about some of the advantages to encryption before getting into how it actually works. Their example script is separated out into three PHP files - the main part of the script, a single-use script that, in turn, creates the third file, include file for the encode/decode functions. With the structure defined, they move on to the code - the generation of the file with the large multi-dimensional array and the two functions to encode and decode the information.