wpa_background - Background information on Wi-Fi Protected Access and IEEE
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
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 mechanism (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 encryption 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 mechanism (only the method for
generating master session key changes).
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
wpa_supplicant is copyright (c) 2003-2016, Jouni Malinen <email@example.com> and
contributors. All Rights Reserved.
This program is licensed under the BSD license (the one with advertisement