encryption of critical data

Hi, Can someone provide me some information about encryption and decryption of critical data such as credit number card in order to stock them on a mysql database in a secure way. What I want to do is making a web interface secured via SSL in order to be able to consult some people information. As I don't want the critical information to be plaintext on the db, I'm searching for a way to get it encrypted and then decrypted when I'm consulting via the interface. I've read the php.net documentation and many articles about data encryption/decryption but both of them stand theorical about the various algorithms. Do you know the more secures of them and the way to use them ? Do you know people working in the same way or do they prefer another kind of more secure solution ? Thank you for your advice, R.