PHP：如何安全地解决PHP多类扩展限制

I have a class (crypt) that helps me encrypt, decrypt. Then, another class (sess) for session starting, restricting and protecting pages. Then, another class (db) for storing session variables, sometimes by encryption like login time, logout time, server referrer etc. Now, with all this, how do I gain access to the three classes different functions in each of those classes as I can only extend one? The Crypt class is just helping to encrypt,I need it in almost every other class.furthermore, I know this questiön has been so answered that its becoming rhetoric but my main enquiry is the 'safest' method.I have a class (crypt) that helps me encrypt, d