PHP, MySQL - how to store important information?

Question

MySQL

Not account passwords, but, for example, mobile phones, mail passwords and other information that is not entirely correct to store in clear text.
The idea was to encrypt with the key and decrypt when needed. Then, even if the database is merged, nothing will change and personal data will remain hidden.
How to do it right ?

Answer 1

The first rule is not to give signs of data.
The second is to encrypt the database using built-in tools ( for mysql ).
Third - do not store the key and the database with the same host.
Fourth - data that does not require processing on the server side, but only requires storage and modification by the client (s) - is always encrypted and decrypted on the client side using the client key. The key is never sent to the server!