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Wi-Fi Protected Access (WPA and WPA2) is a class of systems to secure wireless (Wi-Fi) computer networks. It was created in response to several serious weaknesses researchers had found in the previous system, Wired Equivalent Privacy (WEP). WPA implements the majority of the IEEE 802.11i standard, and was intended as an intermediate measure to take the place of WEP while 802.11i was prepared. WPA is designed to work with all wireless network interface cards, but not necessarily with first generation wireless access points. WPA2 implements the full standard, but will not work with some older network cards.

Contents 1 History 2 WPA2 3 Security in pre-shared key mode 4 EAP types under WPA- and WPA2- Enterprise 5 References 6 External links

WPA was created by the Wi-Fi Alliance, an industry trade group, which owns the trademark to the Wi-Fi name and certifies devices that carry that name.

WPA was designed to enhance the security of wireless networks. There are two flavors of WPA: enterprise and personal. Enterprise is meant for use with an IEEE 802.1X authentication server, which distributes different keys to each user. Personal WPA utilizes less scalable "pre-shared key" (PSK) mode, where every allowed computer is given the same passphrase. In PSK mode, security depends on the strength of the passphrase. The design of WPA is based on a Draft 3 of the IEEE 802.11i standard.

The Wi-Fi Alliance created WPA to enable introduction of standard-based secure wireless network products prior to the IEEE 802.11i group finishing its work. The Wi-Fi Alliance at the time had already anticipated the WPA2 certification based on the final draft of the IEEE 802.11i standard. Therefore, they intentionally made the tags on the frame fields (also known as information elements, or IEs) different from 802.11i to avoid the confusion in unified WPA/WPA2 implementations.

Data is encrypted using the RC4 stream cipher, with a 128-bit key and a 48-bit initialization vector (IV). One major improvement in WPA over WEP is the Temporal Key Integrity Protocol (TKIP), which dynamically changes keys as the system is used. When combined with the much larger initialization vector, this defeats the well-known key recovery attacks on WEP.

In addition to authentication and encryption, WPA also provides vastly improved payload integrity. The cyclic redundancy check (CRC) used in WEP is inherently unsecure; it is possible to alter the payload and update the message CRC without knowing the WEP key. A more secure message authentication code (usually known as a MAC, but here termed a MIC for "message integrity code") is used in WPA, an algorithm named "Michael". The MIC used in WPA includes a frame counter, which prevents replay attacks being executed.

By increasing the size of the keys and IVs, reducing the number of packets sent with related keys, and adding a secure message verification system, WPA makes breaking into a wireless LAN far more difficult. The Michael algorithm was the strongest that WPA designers could come up with that would still work with most older network cards. Due to inevitable weaknesses of Michael, TKIP will shut down the network for one minute if two frames are discovered that fail the Michael check after passing all other integrity checks that would have caught noisy frames. It will then require generation of new keys and reauthentication when the network restarts, forcing the attacker to start over.

Main article: IEEE 802.11i

WPA2 implements the mandatory elements of 802.11i. In particular, in addition to TKIP and the Michael algorithm, it introduces a new AES-based algorithm, CCMP, that is considered fully secure. From March 13, 2006, WPA2 certification is mandatory for all new devices wishing to be Wi-Fi certified.

Pre-shared key mode (PSK, also known as personal mode) is designed for home and small office networks that don't require the complexity of an 802.1X authentication server. Each user must enter a passphrase to access the network. The passphrase may be from 8 to 63 printable ASCII characters or 64 hexadecimal digits (256 bits).^[1] If you choose to use the ASCII characters, a hash function reduces it from 504 bits (63 characters * 8 bits/character) to 256 bits (using also the SSID). The passphrase may be stored on the user's computer at their discretion under most operating systems to avoid re-entry. The passphrase must remain stored in the Wi-Fi access point.

Security is strengthened by employing a PBKDF2 key derivation function. However, the weak passphrases users typically employ are vulnerable to password cracking attacks. To protect against a brute force attack, a truly random passphrase of at least 20 characters should be used, and 33 characters or more is recommended.^[2]

Some consumer chip manufacturers have attempted to bypass weak passphrase choice by adding a method of automatically generating and distributing strong keys through a software or hardware interface that uses an external method of adding a new Wi-Fi adapter or appliance to a network. These methods include pushing a button (Broadcom SecureEasySetup^[3] and Buffalo AirStation One-Touch Secure System) and entering a short challenge phrase through software (Atheros JumpStart^[4]). The Wi-Fi Alliance has standardized these methods in a program called Wi-Fi Protected Setup (formerly Simple Config).

The Wi-Fi alliance has announced the inclusion of additional EAP (Extensible Authentication Protocol) types to its certification programs for WPA- and WPA2- Enterprise. This was to ensure that WPA-Enterprise certified products can interoperate with one another. Previously, only EAP-TLS (Transport Layer Security) was certified by the Wi-Fi alliance.

The EAP types now included in the certification program are:

• EAP-TLS (previously tested)
• EAP-TTLS/MSCHAPv2
• PEAPv0/EAP-MSCHAPv2
• PEAPv1/EAP-GTC
• EAP-SIM

Other EAP types may be supported by 802.1X clients and servers developed by specific firms. This certification is an attempt for popular EAP types to interoperate; their failure to do so is currently one of the major issues preventing rollout of 802.1X on heterogeneous networks.

• Wi-Fi Alliance's WPA page
• Wi-Fi Alliance's Interoperability Certificate page
• EAP types supported under WPA-Enterprise
• Wi-Fi Alliance. (2003). Wi-Fi Protected Access: Strong, standards-based, interoperable security for today’s Wi-Fi networks. Retrieved March 1, 2004.
• Wi-Fi Alliance. (2004). Wi-Fi Protected Access security sees strong adoption: Wi-Fi Alliance takes strong position by requiring WPA security for product certification. Retrieved January 5, 2004.
• Weakness in Passphrase Choice in WPA Interface, by Robert Moskowitz. Retrieved March 2, 2004.
• Press Release about new EAP types supported under WPA-Enterprise.
• IEEE Std. 802.11i-2004