You can use the mcrypt library in PHP ( http://php.net/manual/en/book.mcrypt.php ), it supports all the basic cryptographic algorithms. I suggest you use AES-128, it is a kind of industry standard. Just make sure you keep the key in a safe place. Then you can encrypt your data, convert it to base64 and save it in your database. Whenever you need to use data, just retrieve it from the database and apply the inverse operations.
I am not familiar with how MySQL works exactly. Maybe it is possible to store data in encrypted form and whether to keep your key somewhere safe?
From a security point of view, the PHP method will be better because the data coming from your database and coming from your database is still encrypted.
Please do not use XOR cypher, at best it is funny. The only leaked pair of open ciphertext will show your full key ( plaintext XOR ciphertext = key ). This provides perfect protection when used as a disposable panel . Of course, you cannot use this, because now you need to use a different key for each piece of data and , in some way, to safely store all of these disposable pads. Maybe you can use encryption for this;) ...? (insert an infinite loop here).