by Dave Odom. CISSP

The Wireless Security Landscape

In the span of a year the wireless networking landscape has had radical movement towards providing not only the traditional benefits of wireless networking (mobility, scalibility, and cost effectiveness), but most importantly security. Security in 802.11, seen by industry as the wireless networking solution of choice, has been viewed as somewhat of an oxymoron. Vulnerable wireless networks are often the ‘Achilles Heel’ of network infrastructures and used by attackers to facilitate further access to the otherwise protected enterprise LAN. Numerous articles have littered technical publications, general public newspapers, and TV news broadcasts of how insecure wireless networks have resulted in legal cases from ‘wardriving’ to illegal financial record access and credit card fraud. This is a major reason preventing 802.11 wireless networking solutions from being adopted by corporations and businesses that demand confidentiality and integrity in support of sensitve internal and E-business communications.

Enter 802.11i, the much anticipated upgrade to 802.11 security ratified in June of 2004 by the IEEE standards committee. 802.11i is the ‘last mile’ to providing strong authentication and privacy mechanisms for a protocol standard desperately in need of a security facelift. Combined with a solid backing from vendors, who have begun certification and availability of products, it appears the waters are safe for implementing wireless networking across the enterprise. Let’s examine the history surrounding the need for 802.11i, its security features, and challenges to full adoption as a viable and secure wireless networking solution.

Security and 802.11

 The original 802.11 standard was not designed to provide strong authentication and encyption mechanisms. The primary security features of 802.11 were incorporated at the data link layer and rely on the Wired Equivalent Privacy (WEP) protocl. The 802.11 WEP standard offers 64-bit (128-bit in vendor implementations) encryption using the RC4 cryptographic (stream cipher) algorithm. The WEP encyrption key is comprised of a 40-bit shared key and a 24-bit initialization vector (IV) that is used to provide limited authentication and privacy through the use of a single shared key that is distributed to end user wireless systems.

Unfortunately, the WEP protocol implemented the RC4 encryption algorithm in a flawed manner and neglected to include a key management protocol. The use of static, reusable shared secret keys and IVs being transmitted in clear text led to several public exploits being developed to break wireless transmissions encrypted with WEP.

An improvement to 802.11 security standards was in order, based on WEP’s lack of viable authentication mechanism and weakness of its encryption scheme. Orignially, improvements to the authentication issue came with 802.1x (an authentication standard for both wired and wireless networks) that made use of an Extensible Authentication Protocol (EAP) method that allows you to choose from a variety of authentication mechanisms including: EAP-MD5, LEAP, PEAP, EAP-TLS and EAP-TTLS that are traditionally implemented through an authentication server (e.g. RADIUS).

In October of 2002, the Wi-Fi Alliance announced that it would develop a new interim security specification that could be incorporated into certified Wi-Fi compliant devices called Wi-Fi Protected Access (WPA). WPA, which relied upon an interim version of 802.11i does not rely on the use of fixed WEP keys, but uses a new protocol known as Temporal Key Integrity Protocol (TKIP) that initiates a key rotation every 10,000 bytes of data. TKIP, which provides the improved confidentiality and integrated mechanisms, increases the standard size of the WEP key fro 40 to 128-bits and does not use a single static key, but instead uses keys that are dynamically generated and distributed by an authentication server. WPA still makes use of the RC4 encryption cipher but allows for the use of existing technology such as IEEE 802.1x, EAP, and RADIUS authentication methods. These solutions, however; only provided the "band-aid" to problems with 802.11 security and required in many cases adding increased complexity to the wired and wireless infrastructure.

802.11i and WPA2

Released in June 2004, 802.11i was designed by the IEEE to provide the final security solution set to the WLAN, as well as provide improved network access management features. 802.11i replaces the notoriously insecure WEP with the option of two robust encryption protocols in TKIP and the Counter Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP). CCMP improves WEP by introducing a new government approved (FIPS 140-2) encryption standard known as the Advanced Encryption Algorithm (AES). AES is a symmetric (i.e. same key is used for both encryption and decryption) block cipher where there are multiple encryption phases that data undergoes. The standard for AES is 128-bit encryption, but it supports key lengths up to 256-bits.

802.11i relies on the 802.1x authentication scheme for providing strong two-way/mutual authentication between a client and authentication server, authenticating the identity of the user not just the device. This was a radical improvement to the inherent flaw in 802.11 which provided only one-way authentication and contained no provisions for a per-packet validation scheme to identify the packet source, leaving authentication process susceptible man-in-the-middle attacks.

In order to maintain a standard for interoperability in products that implemented the features of 802.11i, the Wi-Fi Alliance (as with WPA) established a certification program for equipment and software known as WPA2. The features of IEEE 802.11i are specified in WPA2, but WPA2 defines for industry the set of mandatory features that will be included in WPA2 certified devices. A list of WPA2 certified devices can be found on the WiFi Alliance website. Vendors currently offering WPA2 compliant products include: Atheros, Broadcom, Cisco, Conexant, D-Link, IBM, Intel, Netgear and Proxim.

Challenges to 802.11i Adoption

Although 802.11i provides the long awaited security consumers have demanded, there are still various challenges to its implementation. Issues regarding client mobility are seen as performance suffers during the 802.11i authentication process when users roam between WLAN cells and attempt to exchange their security credentials during reassociation. This process can drastically affect time-sensitive voice and video applications that may be critical for the end user to maintain. Interoperability among vendors, in spite of the WiFi Alliance WPA2 certification, standard may hamper widespread deployments. This is primarily due to the fact that the WiFi Alliance is only testing for interoperability with the AES encrption standard. Testing interoperability for the various vendor implementations of authentication mechanisms is yet to be incorporated. This could force organizations to adopt single source vendors for their WLAN equipment procurements, limiting their choice of options and wireless vendor feature sets. Furthermore, the enhanced elements of 802.11i (AES) requires existing consumers to upgrade their WLAN infrastructure hardware, which for many large organizations is not cost effective.

Summary

While 802.11i is not necessarily the "silver bullet" to WLAN security, it does provide a robust level of protection in comparison with its predecessor. Organizations requiring that level of privacy and authentication should weigh the associated risk of not adopting the technology against the challenges and cost of migration. Many federal departments and agencies will be forced to implement 802.11i (or a similar technology offering compatible security) throughout their WLAN enterprises based on regulatory compliance with federal guidelines for the security of information systems (e.g. FISMA, SARBOX, and HIPAA). Security professionals should continue to view wireless networking solutions and its associated security standards as a technology in its infancy stages as there will undoubtedly be modifications and enhancements to the existing standards as their use and requirements evolve.