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WPA_BACKGROUND(8) WPA_BACKGROUND(8)

NAME
wpa_background - Background information on Wi-Fi Protected Access and IEEE 802.11i

WPA
The original security mechanism of IEEE 802.11 standard was not designed to be strong and has proven to be insufficient
for most networks that require some kind of security. Task group I (Security) of IEEE 802.11 working group
(http://www.ieee802.org/11/) has worked to address the flaws of the base standard and has in practice completed its work
in May 2004. The IEEE 802.11i amendment to the IEEE 802.11 standard was approved in June 2004 and published in July 2004.

Wi-Fi Alliance (http://www.wi-fi.org/) used a draft version of the IEEE 802.11i work (draft 3.0) to define a subset of
the security enhancements that can be implemented with existing wlan hardware. This is called Wi-Fi Protected Access<TM>
(WPA). This has now become a mandatory component of interoperability testing and certification done by Wi-Fi Alliance.
Wi-Fi provides information about WPA at its web site (http://www.wi-fi.org/OpenSection/protected_access.asp).

IEEE 802.11 standard defined wired equivalent privacy (WEP) algorithm for protecting wireless networks. WEP uses RC4 with
40-bit keys, 24-bit initialization vector (IV), and CRC32 to protect against packet forgery. All these choices have
proven to be insufficient: key space is too small against current attacks, RC4 key scheduling is insufficient (beginning
of the pseudorandom stream should be skipped), IV space is too small and IV reuse makes attacks easier, there is no
replay protection, and non-keyed authentication does not protect against bit flipping packet data.

WPA is an intermediate solution for the security issues. It uses Temporal Key Integrity Protocol (TKIP) to replace WEP.
TKIP is a compromise on strong security and possibility to use existing hardware. It still uses RC4 for the encryption
like WEP, but with per-packet RC4 keys. In addition, it implements replay protection, keyed packet authentication mecha-
nism (Michael MIC).

Keys can be managed using two different mechanisms. WPA can either use an external authentication server (e.g., RADIUS)
and EAP just like IEEE 802.1X is using or pre-shared keys without need for additional servers. Wi-Fi calls these "WPA-
Enterprise" and "WPA-Personal", respectively. Both mechanisms will generate a master session key for the Authenticator
(AP) and Supplicant (client station).

WPA implements a new key handshake (4-Way Handshake and Group Key Handshake) for generating and exchanging data encryp-
tion keys between the Authenticator and Supplicant. This handshake is also used to verify that both Authenticator and
Supplicant know the master session key. These handshakes are identical regardless of the selected key management mecha-
nism (only the method for generating master session key changes).

IEEE 802.11I / WPA2
The design for parts of IEEE 802.11i that were not included in WPA has finished (May 2004) and this amendment to IEEE
802.11 was approved in June 2004. Wi-Fi Alliance is using the final IEEE 802.11i as a new version of WPA called WPA2.
This includes, e.g., support for more robust encryption algorithm (CCMP: AES in Counter mode with CBC-MAC) to replace
TKIP and optimizations for handoff (reduced number of messages in initial key handshake, pre-authentication, and PMKSA
caching).