Features

WiFi's Protected Access wireless: the background

There had to be an upgrade for Wireless Lan security. Over the past year, many WiFi Alliance members and their customers have become increasingly concerned about the vulnerabilities of Wired Equivalent Privacy (WEP), the basic mechanism to date for interoperable security in WiFi certified products. In response, the WiFi Alliance - in conjunction with the IEEE - has driven an effort to bring strongly enhanced, interoperable WiFi security to market in the first quarter of 2003. The result of this effort is WiFi Protected Access (WPA).

Overview

WiFi Protected Access is a specification of standards-based, interoperable security enhancements that strongly increase the level of data protection and access control for existing and future wireless LAN systems.

Designed to run on existing hardware as a software upgrade, WiFi Protected Access is derived from and will be forwardcompatible with the upcoming IEEE 802.11i standard.

When properly installed, it will provide wireless LAN users with a high level of assurance that their data will remain protected and that only authorized network users can access the network. The WiFi Alliance plans to begin interoperability certification testing on WiFi Protected Access products starting in February 2003.

WEP Vulnerabilities

Not long after its development, WEP's cryptographic weaknesses began to be exposed. A series of independent studies from various academic and commercial institutions found that even with WEP enabled, third parties can breach WLAN security. A hacker with the proper equipment and tools can collect and analyze enough data to recover the shared encryption key. Although such security breaches might take days on a home or small business WLAN where traffic is light, it can be accomplished in a matter of hours on a busy corporate network.

Despite its flaws, WEP provides some margin of security compared with no security at all and remains useful for the casual home user for purposes of deflecting would-be eavesdroppers. For large enterprise users, WEP native security can be strengthened by deploying it in conjunction with other security technologies such as Virtual Private Networks or 802.1x authentication with dynamic WEP keys. Nevertheless, WiFi users demanded a strong, interoperable, and immediate security enhancement native to WiFi. The result of this demand is WiFi Protected Access.

WiFi Protected Access

WiFi Protected Access had several design goals, i.e.,: be a strong, interoperable, security replacement for WEP, be software upgradeable to existing WiFi certified products, be applicable for both home and large enterprise users, and be available immediately.

To meet these goals, two primary security enhancements needed to be made. WiFi Protected Access was constructed to provide an improved data encryption, which was weak in WEP, and to provide user authentication, which was largely missing in WEP.

Enhanced Data Encryption through TKIP

To improve data encryption, WiFi Protected Access utilizes its Temporal Key Integrity Protocol (TKIP). TKIP provides important data encryption enhancements including a per-packet key mixing function, a message integrity check (MIC) named Michael, an extended initialization vector (IV) with sequencing rules, and a re-keying mechanism. Through these enhancements, TKIP addresses all WEP's known vulnerabilities.

Enterprise-level User Authentication via 802.1x and EAP

WEP has almost no user authentication mechanism. To strengthen user authentication, WiFi Protected Access implements 802.1x and the Extensible Authentication Protocol (EAP). Together, these implementations provide a framework for strong user authentication. This framework utilizes a central authentication server, such as RADIUS, to authenticate each user on the network before they join it, and also employs "mutual authentication" so that the wireless user doesn't accidentally join a rogue network that might steal its network credentials.

WiFi Protected Access and IEEE 802.11i Comparison

WiFi Protected Access will be forward-compatible with the IEEE 802.11i security specification currently under development by the IEEE. WiFi Protected Access is a subset of the current 802.11i draft, taking certain pieces of the 802.11i draft that are ready to bring to market today, such as its implementation of 802.1x and TKIP.

These features can also be enabled on most existing WiFi certified products as a software upgrade. The main pieces of the 802.11i draft that are not included in WiFi Protected Access are secure IBSS, secure fast handoff, secure de-authentication and disassociation, as well as enhanced encryption protocols such as AES-CCMP. These features are either not yet ready for market or will require hardware upgrades to implement. The IEEE 802.11i specification is expected to be published at the end of 2003.

WiFi Protected Access for the Enterprise

WiFi Protected Access effectively addresses the WLAN security requirements for the enterprise and provides a strong encryption and authentication solution prior to the ratification of the IEEE 802.11i standard. In an enterprise with IT resources, WiFi Protected Access should be used in conjunction with an authentication server such as RADIUS to provide centralized access control and management.

With this implementation in place, the need for add-on solutions such as VPNs may be eliminated, at least for the express purpose of securing the wireless link in a network.

WiFi Protected Access for Home/SOHO

In a home or Small Office/ Home Office (SOHO) environment, where there are no central authentication servers or EAP framework, WiFi Protected Access runs in a special home mode. This mode, also called Pre-Shared Key (PSK), allows the use of manually-entered keys or passwords and is designed to be easy to set up for the home user.

All the home user needs to do is enter a password (also called a master key) in their access point or home wireless gateway and each PC that is on the WiFi wireless network. WiFi Protected Access takes over automatically from that point.

Security requirements vary depending on the amount of network traffic and the level of secrecy required for the information being exchanged and the applications being used. While professional users typically require enterprise-quality security to allow secure conduct of confidential business, the security requirements of casual low-volume home users, using their network to print or share files, surf the Internet or exchange email with friends and family, tend to be less stringent.

WiFi Protected Access is designed to meet these different requirements by running in two different modes – enterprise and home mode. In enterprise mode, a network server and sophisticated authentication mechanisms are utilized and automatically distribute special encryption keys, called master keys.

In a home environment, where there are no network servers, WiFi Protected Access runs in a special mode, which allows the use of manually entered keys or passwords instead. This mode, also called Pre-Shared Key (PSK), is designed to be easy to set up for the home user. All the home user needs to do is enter a password (also called a master key) into their access point or home wireless gateway and each PC that is on the WiFi wireless network.

After entering the password, WiFi Protected Access automatically takes over. First, it keeps out eavesdroppers and other unauthorized users by requiring all devices to have the matching password. Second, the password kicks off the encryption process, which in WiFi Protected Access is called Temporal Key Integrity Protocol (TKIP).

This is where the mechanics of WiFi Protected Access are substantially different from WEP, where the same static encryption key is used over and over again. TKIP takes the original master key only as a starting point and derives its encryption keys mathematically from this master key. TKIP then regularly changes and rotates the encryption keys so that the same encryption key is never used twice.

This all happens in the background automatically, invisible to the user. Together, these features make WiFi Protected Access a far stronger security solution than WEP.

While no security mechanism can be considered "absolutely secure," the protection given by WiFi Protected Access in PSK mode is strong enough to prevent most attacks, even sophisticated ones. As such, WiFi Protected Access offers a pragmatic, economical security mechanism for most home users.

It is worth mentioning that telecommuters and other professionals, while they may be physically working from home, may have more stringent enterprise-class security requirements, which may be more than WiFi Protected Access in home mode can offer. It is recommended that these users consult with their IT administrator for details.

A useful benefit of WiFi Protected Access is that it is designed to be software upgradeable for existing WiFi certified products, which means that in most cases, existing products will not need to be replaced. So, if you are already using WiFi certified products, your product vendor may be able to send you the appropriate software upgrade.

If you are looking for new WiFi products, look for products that are both WiFi certified (displaying the WiFi logo) and include WiFi Protected Access.

WiFi Protected Access for Public Access

The intrinsic encryption and authentication schemes defined in WiFi Protected Access may also prove useful for Wireless Internet Service Providers (WISPs) offering WiFi public access in "hot spots" where secure transmission and authentication is particularly important to users unknown to each other.

The authentication capability defined in the specification enables a secure access control mechanism for the service providers and for mobile users not utilizing VPN connections.

WiFi Protected Access in "Mixed Mode" Deployment

In a large network with many clients, a likely scenario is that access points will be upgraded before all the WiFi clients.

Some access points may operate in a "mixed mode", which supports both clients running WiFi Protected Access and clients running original WEP security. While useful for transition, the net effect of supporting both types of client devices is that security will operate at the less secure level (WEP), common to all the devices.

Therefore, organizations will benefit by accelerating the move to WiFi Protected Access for all WiFi clients and access points.

In summary, WiFi Protected Access is designed to meet the requirements of both large business users and the typical home user. The PSK home mode of operation of WiFi Protected Access offers greatly strengthened security over WEP, and has been specifically designed for home users. The WiFi Alliance plans to begin interoperability certification testing on WiFi Protected Access starting in February 2003.

This article is available as an Acrobat PDF file from the WiFi Alliance. See also a second article on home use, which is incorporated above.