Deploying a Secure Wireless Network
Although volumes could be (and have been) written on wireless security, I would just like to discuss the 10,000-foot view of wireless security. This will give you an idea of the areas of focus when you are considering using wireless networking technology in your organization. As soon as you understand these areas, you can begin digging deeper into the technology to find the
right fit for your wireless design.
The CCENT and CCNA certifications require only a foundational understanding of wireless security topics, which are discussed in this book.
Wireless security can be broken into three major categories: encryption, authentication, and detection.
- Compare and contrast wireless security features and capabilities of WPA security (including: open, WEP, WPA-1/2)
When you’re ready for a technology roller coaster ride, begin studying the history of wireless encryption standards. I mentioned in the preceding chapter that wireless networking technology is so amazing that companies began using it long before the security standards were heavily tested and proven to withstand attacks. So, fasten your seat belt, and let’s ride through the
evolution of wireless encryption standards, starting where it all began: with WEP.
Wired Equivalent Privacy (WEP)
The WEP standard was the first measure of security released for wireless networking. This encryption method was based on the simple concept of using preshared keys (PSKs) to generate an encryption algorithm. Here’s an overview of how the WEP encryption algorithm works:
The WEP standard uses an encryption formula called RC4. This is essentially a mathematical formula that takes every piece of data you want to encrypt and scrambles it. The missing piece of this formula is the PSK, which you enter. This is visually demonstrated in Figure 18.1.
When the wireless access point receives data, it uses the reverse formula to decrypt the data. So, for WEP to work successfully, you must manually enter the PSK on both the wireless client and the wireless access point.
When WEP was originally released (in 1997), it used 64-bit encryption, which is considered weak by today’s standards. You can compare 64-bit encryption to a math formula with 64 steps. Each step scrambles the original data more and more.
The more bits you use for encryption, the more complex your encryption algorithm, and the more difficult it is to break. However, the more bits you use for encryption, the harder it is for your network device to communicate because of the processing power needed. This may result in slower network communication.
Unfortunately, within a few years of WEP’s initial release, major security vulnerabilities were found. The wireless standards groups improved the strength of the WEP algorithm by releasing a 128-bit version in 2002, which some people refer to as WEP2. Although it makes the algorithm slightly more difficult to break, many flaws in the underlying design of WEP caused
this security standard to crumble. Wireless security was suffering in a huge way when WPA was released.
Remember that WEP offers 64-bit and 128-bit encryption strengths. Also, keep in mind that the WEP stan dard allows only static, preshared keys.
Wi-Fi Protected Access (WPA)
The wireless networking industry faced a major issue. A newer encryption algorithm was needed to combat the weaknesses of WEP, but the more complex encryption algorithms would require more-powerful 802.11-compatible wireless hardware to process the algorithm. By this point, the industry had already purchased millions of wireless access points and wireless cards, so simply saying, “Sorry! Go ahead and scrap all that equipment and buy new stuff.” was not an option. In 2003 the Wi-Fi Alliance (a group of extremely smart people sponsored by many organizations) stepped forward and proposed WPA.
WPA used a new encryption algorithm called Temporal Key Integrity Protocol (TKIP). TKIP ran on the same wireless hardware that was originally created, and it used a 128-bit encryption algorithm. It was engineered to dramatically increase the number of encryption keys that could be used and virtually eliminated the attacks that were successful on WEP keys. Although WPA was not flawless, it was a tremendous step forward from the original WEP standard.
Wi-Fi Protected Access, Reloaded (WPA2 and 802.11i)
WPA was never meant to solve the world’s wireless security problems. Although it was much more secure than WEP, it did have the weakness of using the same old hardware that WEP used. Inherent in that hardware were a few security weaknesses that simply could not be overcome by changing the encryption formula. For that reason, the Wi-Fi Alliance quickly (in 2004) proposed an alternative standard casually called WPA2 and officially called 802.11i.
WPA2 uses a completely different encryption standard known as Advanced Encryption Standard (AES). This encryption standard was standardized by the U.S. government and has been extensively analyzed and tested. The WPA2 standard left behind the old hardware and required that users purchase new wireless hardware (both cards and access points).
To ease the transition, WPA2 hardware can run in backward-compatibility mode to support the original WPA and even WEP standards. This allows an organization to upgrade its wireless access points to the new hardware and still support the older WEP- and WPA-compliant clients. As the clients upgrade to newer wireless devices, WPA2 (and thus AES encryption) can be used.
WPA uses TKIP encryption, and WPA2 uses AES.
Wireless Authentication (802.1x)
The wireless encryption we’ve discussed so far does indeed secure the data, but it has a couple of weaknesses. First, using a preshared key system means that you must go to every wireless device and accurately enter the PSK before the device can communicate on the network. Likewise, keeping the same PSK for an extended amount of time increases the chances of the
encryption algorithm’s being hacked, so it’s a good idea to change the PSK on a regular basis.
In a small network of 10 or so wireless devices, this may not be a big deal, but in a large network with hundreds or even thousands of wireless devices, this can be a full-time job. The second issue presented by a PSK system is the inability to remove access. For example, if you are using a PSK among your 50 laptop users on the network, and one of the users leaves the company, you must change the PSK for the 49 other wireless users to eliminate the security vulnerability from the former employee.
Simply relying on a shared PSK among all devices is not a secure or scalable solution for business. What was needed was a method of wireless authentication. This would allow you to have a system of granting or restricting access based on a variety of criteria, such as usernames and passwords or certificates. The industry responded with the ultimate authentication method,
which we now know as 802.1x.
Usually when we think of network authentication, we think of accessing an operating system. For example, when you log into a Microsoft Windows domain, you must authenticate using a username and password to gain access to shared resources on the Windows-based servers.
When you Telnet to a Cisco device, you must authenticate to gain access to manage the device using the Cisco IOS. 802.1x takes authentication to an entirely new level. Now, you must authenticate to gain access to the Layer 2 LAN network fabric. Now, to access the wireless access point and use the 802.11 network, you must authenticate. You can also apply 802.1x to LAN network switches. When a device plugs into an Ethernet port, it must authenticate before it gains access to that port and, thus, the network.
Think of the possibilities as soon as you begin using network authentication! When a user leaves the company, you can negate her user account on a Microsoft Windows server. This will cause her to lose the ability to log on to the Windows workstation and, at the same time, lose the ability to even plug into a switch port or attach to the wireless network! Talk about cutting
off a user! Now, let me give you the basics of how this works. 802.1x designates three network devices that participate in network authentication: the supplicant, the authenticator, and the authentication server. Figure 18.2 shows the placement of
When the user wants to access the network, he must first send his authentication credentials (such as a username and password) to the authenticator, which forwards them to the authentication server. When the authentication server receives the credentials, it checks them against its database and then tells the authenticator whether the device has passed authentication. If
the device fails authentication, its access to the network is terminated or severely limited, depending on how you (as the administrator) decide to restrict the device. If the device passes authentication, the supplicant and authentication server generate a dynamic encryption key known as the session key. This provides the same security as the PSK but does not require you to enter a PSK on the client or wireless access point.
I could say much more about network authentication, but, as I said at the beginning of this section, this is a 10,000-foot overview of the concepts. You now know what network authentication is all about and what it is used for. It’s now up to you to continue past the CCNA in your Cisco studies to determine the best method to implement network authentication. Proceed
into that world with a grave warning: Don’t let the EAP monsters eat you alive! Don’t worry; you’ll know what I mean when you get there.
Keep in mind that WPA and WPA2 standards allow for static PSKs or dynamic keys when used with 802.1x. WEP allows only static PSKs.
Wireless Intrusion Prevention System (IPS)
By using wireless network authentication and encryption, we have addressed the concerns of war driving and network hackers. But what about those pesky users who plug unauthorized wireless access points into the network? For that we have wireless IPS. You can think of IPS as introducing a variety of detection lasers into your network. I think back to the 1996 movie Mission Impossible with Tom Cruise.
In one scene, Cruise (well, Ethan Hunt, to be exact) must retrieve a chip from a secured computer room by twisting and contorting his body through a variety of lasers projected around the room. In the same sense, deploying wireless IPS for your network sets up a variety of “sensors” that detect when a policy has been violated. The minute a rogue access point shows up in the network, the system can alert you, pinpointing the location of the access point on a map of your campus. Amazing!
Network-wide IPS can detect a variety of additional suspicious movements around the network, in both the wired and wireless worlds. However, discussing the rest of those detections is part of the Cisco Certified Security Professional (CCSP) certification.