php - Cookies vs. sessions

Question

I started using PHP a couple of months ago. For the sake of creating a login system for my website, I read about cookies and sessions and their differences (cookies are stored in the user's browser and sessions on the server). At that time, I preferred cookies (and who does not like cookies?!) and just said: "who cares? I don't have any good deal with storing it in my server", so, I went ahead and used cookies for my bachelor graduation project. However, after doin' the big part of my app, I heard that for the particular case of storing user's ID, sessions are more appropriate. So I started thinking about what would I say if the jury asks me why have you used cookies instead of sessions? I have just that reason (that I do not need to store internally information about the user). Is that enough as a reason? or it's more than that?
Could you please tell me about advantages/disadvantages of using cookies for keeping User's ID?

Thanks for you all in StackOverflow!

Answer 1

The concept is storing persistent data across page loads for a web visitor. Cookies store it directly on the client. Sessions use a cookie as a key of sorts, to associate with the data that is stored on the server side.

It is preferred to use sessions because the actual values are hidden from the client, and you control when the data expires and becomes invalid. If it was all based on cookies, a user (or hacker) could manipulate their cookie data and then play requests to your site.

Edit: I don't think there is any advantage to using cookies, other than simplicity. Look at it this way... Does the user have any reason to know their ID#? Typically I would say no, the user has no need for this information. Giving out information should be limited on a need to know basis. What if the user changes his cookie to have a different ID, how will your application respond? It's a security risk.

Before sessions were all the rage, I basically had my own implementation. I stored a unique cookie value on the client, and stored my persistent data in the database along with that cookie value. Then on page requests I matched up those values and had my persistent data without letting the client control what that was.