How To Find Keystore In The Laptop What's The Best Way To Store An Encryption Key Using PHP?

What's the best way to store an encryption key using PHP? - how to find keystore in the laptop

We will write a PHP script that reads an encrypted file. But the problem is that not only use the key that can decrypt to save the file in the PHP code. It was recommended that I use and store a key, but not quite understand how it works. Can anyone help point me in the right direction?