Access control is one of the most important elements of security. The object of security is to separate the world into "good guys" and "bad guys." It follows that you cannot achieve security unless you have a mechanism to perform this separation. That mechanism is access control.
On the surface, maintaining control is straightforward. All situations have the following elements:
Suppose a visitor knocks on your front door and your child opens it (with the security chain on). The visitor is the supplicant, your child is the authenticator, and you are the authorizer. Only if you say it's okay will your child take off the security chain and let the visitor in (don't you wish you really had such power!). If you answer the door personally, you take the role of both authenticator and authorizer.
The steps involved in access control follow a similar pattern:
These steps work to control access; but as we discussed in earlier chapters, if the supplicant wants to come and go repeatedly without going through this procedure each time, he needs to obtain some sort of token that proves that he has been authorized. In the case of a corporation, for example, that might be a swipe card that opens the employee entrance door.
So if access control is really this simple, why devote a whole chapter to it? Well, the reality is that while the concept and goals of access control are simple, designing a system that is immune to attack is very difficult. Most of the access control systems dealing with people are trivially easy to fool by an intelligent con man. How many of us have left our swipe card at home one day and, upon arriving at work, just walked in behind another employee? For Wi-Fi LANs, we can't allow even the slightest flaw in the access control method, or else hacker tools will appear on the Internet within months. Getting it right is hard.
This chapter focuses on the three protocols that are used to implement access security in WPA and RSN:
The first two protocols are mandatory for WPA and RSN. RADIUS is the method of choice for WPA and is an option for RSN.
There is much confusion about IEEE 802.1X and what it does. Because it is difficult for customers to fully understand all the elements of security, vendors tend to talk about IEEE 802.1X as if it were the entire security solution for Wi-Fi LANs. In reality, as we will see shortly, IEEE 802.1X is only a small part of the solution, albeit an important one. IEEE 802.1X is the foundation of both WPA and RSN.
Before we look at IEEE 802.1X, let's take a diversion and look at the history of dial-in modem support. "Why now?" you may say. The fact is that the main protocols of EAP and RADIUS were both developed in the context of dial-in access. It turns out that dial-in access control is organized in a very similar way to IEEE 802.1X, which is why the same protocols, EAP and RADIUS, can be applied to both. By reviewing the dial-in case first, you will find that the WPA and RSN cases make more sense.