I'm writing a php application that accepts sensitive customer data, and so I need to encrypt it before storing it in a mysql database. I'm going to use mysql's built-in AES functionality to do column-level encryption.
I want to avoid storing the encryption key on the server, and so i'm going to provide a web-page for an administrator to log-in, and enter the encryption key. I want to store this key in memory while the application is running, but never permanently to disk.
What is the best way to do this?
Can I modify the $_SERVER array to store information between requests? Can I store the key with apache in some way? Maybe shared memory?
Rather than rely on MySQL AES for encryption, why not use PHP's native openssl encryption scheme (a PECL extension). This requires a private and public key, public to encrypt, private to decrypt, and the keys can be kept in separate places.