WPA2: Second Generation WiFi Security

Afraid of security threats over your Wi-Fi network? Upgrade your wireless devices to the most robust and scalable security standard available for Wi-Fi-the WPA2

Monday, May 08, 2006

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Wireless security at the basic level is traditionally implemented using WEP or WPA. WEP as is common knowledge now, is very easy to crack and is not a preferred mechanism for production-class wireless networks. WPA uses TKIP for encryption and TKIP is not considered strong enough to be FIPS 140-2 compliant and hence cannot be used readily by governmental deployments. While the second generation WPA (known as WPA2 or 802.11i) is not designed to replace either WEP or WPA, it is considered the strongest security mechanism thus far. This is because besides TKIP, it can also use AES for encryption. AES encrypted data is considered FIPS 140-2 compliant.

The 802.11i spec (WPA2)
The 802.11i specification for wireless LAN security was ratified by the IEEE in June 2004 in a Standards Committee meeting at Piscataway , NJ . This specification formally replaces WEP and other security features of the original IEEE 802.11 standard. It is also known as WPA2. Both WPA and WPA2 are secure methods of communication using Wi-Fi. If you have equipment that supports only WPA, but not WPA2, it's safe to continue using WPA. However, if you're buying new equipment, you should buy products that support WPA2 with

Enterprise mode. In March, Wi-Fi Alliance announced that the WPA2 security certification program, the second generation of WPA, is now a mandatory feature for all new Wi-Fi certified products.

New security features
Unlike older security standards, all of which define the physical layer issues, WPA2 defines security mechanism that operates between the MAC (Media Access Control) sub layer and the network layer. It has a better 128-bit encryption with TKIP and AES.

TKIP:Unlike WEP, which uses a single key for unicast data encryption and typically a separate key for multicast and broadcast data encryption, WPA2 uses a set of four different keys for each client–AP pair and a set of two different keys for multicast and broadcast traffic.

It derives TKIP using a four-way handshake process that is the same as with WPA. This protocol is perfectly adequate to protect ordinary Wi-Fi transmissions in a SOHO network.

AES: WPA2 equipment can also require AES (Advanced Encryption Standards) for encryption of data. AES was added to WPA to meet the needs of customers who communicate with the US government and others which require this specific algorithm. This is the feature that takes WPA2 a step further than WPA. The downside is that AES support may require new hardware for many existing WLANs, as it needs a dedicated chip to handle the encryption and decryption. But, the good news is that AES meets FIPS (Federal Information Processing Standard) 140-2 requirement, which is a government security criterion and provides stronger encryption than WPA and TKIP.

Authentication process
Like WPA, WPA2 can be enabled in both Enterprise and Personal modes of operation. For Enterprise mode, WPA2 requires authentication in two phases; the first is IEEE 802.1X authentication, which is an open system authentication, and the second uses EAP (Extensible Authentication Protocol). For home or small office networks, WPA2 Personal mode supports the use of PSK (Pre-Shared Key). Based on the EAP or PSK authentication process, WPA2 requires the determination of mutual PMK (Pairwise Master Key) for key management. Personal mode requires only an access point and client device while Enterprise mode typically requires RADIUS (Remote Authentication Dial-In User Service) based authentication or other authentication server on the network.

Tip: If your WiFi usage is in a SOHO network, PSK method of authentication may be adequate for your needs. It is recommended that while using PSK authentication process mode, you should set a password of at least 20 characters and make sure it doesn't contain any names or dictionary words.

Robust Secure Network
Another element of WPA2 standard is RSN (Robust Secure Network). By default, RSN uses AES and  CCMP (Countermode CBC MAC Protocol) and it is this, which provides a stronger and scalable solution. CCMP uses Cipher Block Chaining Message Authentication Code (CBC-MAC). This algorithm produces a Message Integrity Code (MIC) that provides data origin authentication and data integrity for wireless frame. Changing even one bit in a message produces a totally different result. Messages are encrypted using a secret key (128 bits) and a 128 bit block of data. The end result is the encryption that is much harder to break than even WPA.

Fast roaming
During a session, a series of messages are sent between wireless client and wireless access point. While the wireless client roams between wireless access points, there is a noticeable delay to perform authentication, which leads to network interruptions and low connectivity. To minimize the delay of authentication and reduce network interruptions, WPA2 equipment can optionally support PMK caching and preauthentication for fast handoff. Therefore, access is much faster when a wireless client roams back to the wireless access point to which the client has already authenticated. This feature is helpful when there are more than one access points in a network.

PMK caching
PMK caching is a feature through which a user can get re-authenticated quickly to a wireless access point, authenticated to previously. It only needs to perform the four-way handshake and determine new pairwise transient keys. In the request frame, wireless client includes a PMK identifier that was determined during the initial authentication and stored with both the wireless client and wireless AP's PMK cache entries. These entries are stored for a finite amount of time, which are then used for re-authentication process.

Preauthentication
Preauthentication is a process through which a wireless client has an option to perform 802.1X authentication with another wireless AP in its range, while itself already connected to its current AP. Through the existing wireless AP connection, the wireless client sends a preauthentication request to another AP. After that, PMK and its associated information is stored in PMK cache. Now, the wireless client when connecting with the wireless AP to which it has already preauthenticated, only needs to perform a four-way handshake.

In a nutshell
Despite the potential cost of implementing it, the new WPA2 is by far the strongest security system for wireless networks. It's the most robust, scalable and secure solution and will appeal particularly to enterprise users, where key management and administration has been a major headache. WPA2 standard has been specially designed to overcome the major security issues, which were present in the older encryption standards. So WPA2 is the wireless security standard that you can depend on.

Apurva Kothari, MD, Reckon Network

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