Wi-Fi Protected Access (WPA and WPA2) is a certification program developed by the Wi-Fi Alliance to indicate compliance with the security protocol created by the Wi-Fi Alliance to secure wireless computer networks. The Alliance defined the protocol in response to several serious weaknesses researchers had found in the previous system, WEP (Wired Equivalent Privacy).[1]
The WPA protocol implements the majority of the IEEE 802.11i standard. The Wi-Fi Alliance intended WPA as an intermediate measure to take the place of WEP pending the preparation of 802.11i. Specifically, the Temporal Key Integrity Protocol (TKIP), was brought into WPA. TKIP could be implemented on pre-WPA wireless network interface cards that began shipping as far back as 1999 through firmware upgrades. Because the changes required fewer modifications on the client than on the wireless access points (APs), most pre-2003 APs could not be upgraded to support WPA with TKIP. Researchers have since discovered a flaw in TKIP that relied on older weaknesses to retrieve the keystream from short packets to use for re-injection and spoofing.[2]
The later WPA2 certification mark indicates compliance with the full IEEE 802.11i standard. This advanced protocol will not work with some older network cards.[3]
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WPA2 has replaced WPA; WPA2 requires testing and certification by the Wi-Fi Alliance. WPA2 implements the mandatory elements of 802.11i. In particular, it introduces CCMP, a new AES-based encryption mode with mathematically proven security.[4] Certification began in September, 2004; from March 13, 2006, WPA2 certification is mandatory for all new devices to bear the Wi-Fi trademark.[5]
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[6]. Each wireless network device encrypts the network traffic using a 256 bit key. This key may be entered either as a string of 64 hexadecimal digits, or as a passphrase of 8 to 63 printable ASCII characters.[7] If ASCII characters are used, the 256 bit key is calculated by applying the PBKDF2 key derivation function to the passphrase, using the SSID as the salt and 4096 iterations of HMAC-SHA1.[8]
Shared-key WPA remains vulnerable to password cracking attacks if users rely on a weak passphrase.[9][10] To protect against a brute force attack, a truly random passphrase of 13 characters (selected from the set of 95 permitted characters) is probably sufficient.[11] To further protect against intrusion the network's SSID should not match any entry in the top 1000 SSIDs [12]. Massive lookup table have been computated by the Church of Hash (a wireless security research group): at the moment they calculated more than 190 billion (190,000,000,000) hash values for a small number of common SSIDs (NETGEAR, Sitecom, etc)[13].
In November 2008 Erik Tews and Martin Beck - researchers at two German technical universities (TU Dresden and TU Darmstadt) - uncovered a WPA weakness[14] which relied on a previously known flaw in WEP that could be exploited only for the TKIP algorithm in WPA. The flaw can only decrypt short packets with mostly known contents, such as ARP messages. The attack requires Quality of Service (as defined in 802.11e) to be enabled, which allows packet prioritization as defined. The flaw does not lead to key recovery, but only a keystream that encrypted a particular packet, and which can be reused as many as seven times to inject arbitrary data of the same packet length to a wireless client. For example, this allows someone to inject faked ARP packets which makes the victim send packets to the open Internet. This attack was further optimised by two Japanese computer scientists Toshihiro Ohigashi and Masakatu Morii.[15] Their attack doesn't require that Quality of Service has to be enabled. In October 2009, Halvorsen with others made further progress, enabling attackers to inject larger malicious packets (596 bytes, to be more specific) within approximately 18 minutes and 25 seconds.[16] In February 2010, a new attack was found by Martin Beck that allows an attacker to decrypt all traffic towards the client. The authors say that the attack can be defeated by deactivating QoS, or by switching from TKIP to AES-based CCMP.[17]
The vulnerabilities of TKIP are significant in that WPA-TKIP was, up until the proof-of-concept discovery, held to be an extremely safe combination. WPA-TKIP is still a configuration option upon a wide variety of wireless routing devices provided by many hardware vendors.
The Wi-Fi alliance has announced the inclusion of additional EAP (Extensible Authentication Protocol) types to its certification programs for WPA- and WPA2- Enterprise certification programs. 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.
As of 2010[update] the certification program includes the following EAP types:
802.1X clients and servers developed by specific firms may support other EAP types. 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.
Most newer certified Wi-Fi devices support the security protocols discussed above, out-of-the-box: compliance with this protocol has been required for a Wi-Fi certification since September 2003.[18]
The protocol certified through Wi-Fi Alliance's WPA program (and to a lesser extent WPA2) was specifically designed to also work with wireless hardware that was produced prior to the introduction of the protocol[3] which usually had only supported inadequate security through WEP. Many of these devices support the security protocol after a firmware upgrade. Firmware upgrades are not available for all legacy devices.
Furthermore, many consumer Wi-Fi device manufacturers have taken steps to eliminate the potential of weak passphrase choices by promoting an alternative method of automatically generating and distributing strong keys when users add a new wireless adapter or appliance to a network. The Wi-Fi Alliance has standardized these methods and certifies compliance with these standards through a program called Wi-Fi Protected Setup.