Encryption is useful where critical data is being transferred in url. I have found a simple and secure encryption class with some changes to make it fit for new users. You can use it in Codeigniter websites as well. Just copy it in application/libraries directory and use it in other libraries style.
Here is the code for encryption class.
You need to include this class any where in to make your data encrypted with simple encode() or decode() functions.
If you are using it in Codeigniter then use like this