Optimize web and use ajax

I am currently creating a website and I want to make it as optimized as possible. In my case I need to encrypt the text that the user enters by a Text box. But this encryption is private and personal, therefore it will be programmed in PHP so that nobody can access it. What I thought was: Take the text entered by the user using Javascript, call my PHP code through AJAX and return the result. Is it a good way to do it? Thank you very much