Wi-Fi Protected Access (WPA), WPA2 and 802.11i
- Oct 24, 2005
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Wi-Fi Protected Access (WPA), WPA2 and 802.11i
In response to the vulnerability and criticism of WEP, the Wi-Fi Alliance created the Wi-Fi Protected Access (WPA) standard in 2003. WPA was designed to be an interim security solution until the completion of the IEEE 802.11i security standard, and its features are a blend of features originally developed for WEP and those being developed for 802.11i.
Like WEP, WPA uses RC4 encryption for its keys, but unlike WEP, WPA modifies the original key for greater security and supports an optional authentication server. WPA is the minimum recommended security standard for network hardware that supports it, such as 802.11g hardware that supports the full 802.11g standard, and most recent 802.11a hardware. Although some vendors of 802.11b hardware have provided upgrades to support WPA, most 802.11b hardware is not compatible with WPA security.
One of the main complaints about WEP, besides its limited-length keys, is the fact that the same key is used by both sides of the transmission, and the key does not change during a session. These factors make it easy to examine network traffic on a wireless network and eventually crack the encryption key.
WPA solves two problems associated with the earlier WEP security mechanisms. First, it uses encrypted techniques for authentication, which should assist in preventing unauthorized clients from becoming part of the wireless network. Second, it uses a constantly changing key instead of the single shared key used for encryption by WEP. By changing in the encryption key at frequent intervals, WPA can be much more difficult to crack. The constant changing of encryption keys is known as the Temporal Key Integrity Protocol (TKIP). This key-changing method will make it very difficult for intruders to decipher keys used by your wireless network, especially when compared to the static keys known by both sides of the communications link used by the simple WEP standards.
WPA also includes an integrity check that is basically a check sum based on the network packet that can detect whether a packet is originating from a valid network user or an intruder who is attempting to crack the key used by your network. Thus, if an unauthorized user uses the standard techniques to attempt to determine a fixed key, you can detect these intrusion attempts, and then deal with them.
Overcoming Potential Vulnerabilities in WPA
The version of WPA used in SOHO and small-business networks that lack an authentication server is known as WPA-Personal. The encryption key is known as a Pre-Shared Key (PSK); the PSK must be provided by a network client before it can log into a WPA-based wireless network. The original PSK is encrypted using a process known as Temporal Key Integrity Protocol (TKIP), which changes the key repeatedly during a connection to help keep the connection secure. WPA-Personal is also known as WPA-PSK (refer to Figure 24.2).
Although WPA is a stronger encryption standard than WEP, there are several potential weaknesses in the way WPA might be configured by a particular user. These include:
- Encryption keys that are too short—The longer the encryption key, the more secure the network will be. Network experts recommend an encryption key of at least 20 characters.
- Plain-text encryption keys—A key such as "The quick brown fox jumps over the" is certainly longer than the 20-character minimum recommended, but because it is comprised of recognizable words, it would be relatively easy to crack. Instead, use mixed, random alphanumeric keys. For example, a key such as "2F1ACB67EF90O F77A" would be much harder to crack because there are no recognizable words in it.
To see for yourself the threat that short, plain-text encryption keys pose to your WPA-based wireless network, you can download the WPA Cracker utility from tinyPEAP (http://www.tinypeap.com). The network packets WPA Cracker needs for analysis can be gathered with the Ethereal open-source network protocol analyzer available from http://www.ethereal.com. As suggested earlier in this chapter, you should use WPA Cracker and similar tools to analyze your current WPA-based network configuration for vulnerabilities.
To protect yourself against WPA hacking on your home or small-office network, use WPA encryption with a long, random alphanumeric encryption key.
For larger, corporate networks, a more powerful version of WPA known as WPA-Enterprise can be used. WPA-Enterprise (also known as WPA-RADIUS) differs from WPA-Personal in these ways:
- A RADIUS or AAA server is used to authenticate individual users
- Authentication uses the IEEE 802.1X standard developed in 2001
- WPA supports the Extensible Authentication Protocol (EAP)
Regardless of the version of WPA you might select, your wireless access points and network clients must be configured to use the same settings to make a connection possible, just as with the older WEP security standard.
Figure 24.1 shows a typical router being configured to use WPA encryption, and Figure 24.2 shows a matching configuration for a network client running Windows XP.
Figure 24.1 This router is configured to use WPA-Personal encryption.
1. Selects other security settings.
2. Selects security algorithm
3. Shared key; note the mixed alphanumeric text used
4. Specifies time between changes to the original key
5. Saves settings
6. Other security settings available.
7. Opens help screen
Figure 24.2 Configuring a Windows XP client to use WPA-Personal encryption.
1. SSID (wireless network name)
2. Selects network security setting (WPA-PSK = WPA-Personal)
3. Selects encryption type; TKIP is the default for WPA
4. Pre-shared network key (Windows conceals the actual characters for security)
Moving to WPA2 (IEEE 802.11i)
Although WPA, particularly in its WPA-Enterprise version, is much more secure than WEP, it is not as secure as it could be. As mentioned previously in this chapter, WPA was designed as an interim solution until the ratification of the IEEE 802.11i standard could take place. IEEE 802.11i was ratified in 2004, and the first products became available in the fall of 2004. IEEE 802.11i is the basis for WPA2, and WPA2 is the term used to identify IEEE 802.11-based products which meet IEEE 802.11i security standards. WPA2 differs from WPA in the use of a stronger encryption algorithm. While WEP and WPA used RC4 encryption, WPA2 uses the stronger AES encryption algorithm.
To upgrade existing WPA-compatible wireless network hardware to use WPA2 security, you might need to perform one or more of the following operations:
- Download and install updated client device drivers—Note that some client adapters might not support WPA2 security because WPA2 security requires more intensive computation than WPA.
- Download and install updated router and wireless access point firmware—Note that some wireless routes or WAPs might not support WPA2 security because WPA2 security requires more intensive computation than WPA.
Note that some vendors don't explicitly state that their products support WPA2. Instead, they might list the security features the adapters support. Table 24.1 cross-references security features to WPA/WPA2 security standards supported.
Table 24.1 Wireless Security Features/Security Standards Cross-Reference
Equivalent Wi-Fi Security Standard