Standards Watch : Wi-Fi Security Concerns Answered

Wi-Fi’s original security mechanism, Wired Equivalent Privacy (WEP), has been criticized since its inception as being insufficient for securing confidential business communications. The WEP algorithm had contained a number of flaws that seriously undermined the security claims of the system. The Wi-Fi Alliance, however, has developed a new specification addressing the most serious concerns.

WEP Vulnerabilities

WEP uses the RC4 encryption algorithm, which is known as a stream cipher—a type of symmetric encryption algorithm that usually operates on smaller units of plaintext. A stream cipher generates what is called a keystream (a sequence of bits used as a key).

The mode of operation for stream ciphers makes them vulnerable to several attacks, in particular:

• Passive attacks to decrypt traffic based on statistical analysis

• Active attacks to inject new traffic from unauthorized mobile stations based on known plaintext

• Active attacks to decrypt traffic based on tricking the access point

• Dictionary-building attacks that, after analysis of about a day’s worth of traffic, allows real-time automated decryption of all traffic.

Consequently, most enterprise network administrators do not rely on WEP for security and usually employ other measures, such as VPNs, 802.11x technology and existing Web encryption. While WEP is adequate for deterring casual snoopers, more stringent security is needed for important data in wireless networks.

WPA: A Peek Into 802.11i

Because of WEP’s shortcomings, the Wi-Fi Alliance has worked to produce a standard that will serve as an evolutionary step on the way to 802.11i. As a result, the new standard, Wi-Fi Protect Access (WPA), has been derived from the work put forth by the IEEE 802.11i task group.

The WPA standard essentially is an early release of the forthcoming long-term security solution 802.11i draft standard. It essentially gives Wi-Fi users and administrators a sneak preview of the 802.11i capabilities that will answer many, if not all, of WEP’s weaknesses, according to Dorothy Stanley, a member of the Wi-Fi Alliance’s security marketing task force.

Like other Wi-Fi standards, WPA is designed with interoperability and certification of requirements in mind. “WPA will be a spec of standards-based, interoperable security enhancements that is designed to strongly increase the level of data protection [encryption] and access control [authentication] for Wi-Fi wireless LAN systems,” says Stanley.

WPA is designed to be forward-compatible with the 802.11i standard, slated to be published late in 2003. “What is implemented now in WPA will be maintained in 802.11i,” says Stanley. To obtain the more robust advantages of the full 802.11i standard, however, the more than 490 Wi-Fi certified products will have to go through a hardware change at some point.

How WPA Works

WPA will come in the form of upgradeable software for access points. Clients will require a software upgrade for the network interface card, and possibly one for the OS. For enterprise networks, an authentication server supporting RADIUS and the selected extensible authentication protocol (EAP) will be added to the network.

In large networks with many clients, the likely scenario will be that access points will be upgraded before all the Wi-Fi clients can be upgraded. Some access points may support a mixed mode for both clients running WPA and others running the original WEP security. The down side of supporting both modes is that security is no better than the minimum level allowed by the access point—namely, WEP. For that reason, organizations stand to benefit if they upgrade to the WPA standard for all Wi-Fi stations.

Two Modes of Operation

For home and SOHO users, where there are no network servers, the WPA standard runs in a special mode that allows the use of manually entered keys or passwords (pre-shared key mode, PSK) that is easy to set up. All the home user will need is to enter a password (a master key) into his or her access point or home wireless gateway and each PC on that network. After that’s done, WPA security will take over. It will keep out eavesdroppers and unauthorized users by requiring all devices to have the matching password.

Additionally, the password kicks off the encryption process, which in WPA is called Temporal Key Integrity Protocol (TKIP). TKIP is the main differentiator from WEP, which utilizes a static (non-changing) encryption key that is used repeatedly. Within WPA’s TKIP, the original master key is used only as a starting point and derives its encryption keys mathematically from its master key. TKIP then regularly changes and rotates the encryption keys so that the same encryption key is never used twice. This all happens transparently to the user.

Enterprise-class Security

Telecommuters and professionals with more stringent enterprise-class security requirements will benefit from WPA’s mutual authentication, where end-devices and authentication servers send credentials back and forth, thus enabling laptops to authenticate servers and vice versa. Also, the structure of WPA supports caching and precomputation, as well as preventing weak-key attacks, such as those through various WLAN passive monitoring tools that can crack encryption keys on 802.11b networks.

Time Frame

The Wi-Fi Alliance will begin certifying WPA in February. Many Wi-Fi vendors are expecting to ship WPA-protected products by March or April, with a few preparing to do so as early as February.

“We will look at WPA and be compliant with any technology that solves security issues,” says Sean O’Mahony, CEO of FatPort, a Vancouver-based wireless Internet service provider. He says security at the moment is more a matter of perception than technology, as VPNs offer the level of security that most day-to-day business users need. “There were a lot of issues around wireline security that were never addressed,” he says, “so it’s easy to snoop on a wireline connection.” However, O’Mahony notes it’s a different story with wireless connections.

For that reason, this issue is being aggressively debated and may be resolved through WPA and evolving standards like 802.11i. “When rolling out public wireless networks in airports with hotspots, mobile enterprise workers have to feel that their important emails and data transmissions will go securely” says O’Mahony. “So whether through a VPN or other technology means like WPA, we will support it to put our customers at ease.”

Initially, WPA will be optional for obtaining Wi-Fi certification, as the Wi-Fi Alliance will allow vendors a phase-in period. WPA will operate in concert with WEP components. Right now, work to develop a test plan for WPA and a test bed to enable interoperability testing have a target date of Feb. 3 for formal certification.