blob: eb3a0891b7cc06242e871a778ae299834ecb1b55 [file] [log] [blame]
<!doctype refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN">
<refpurpose>Background information on Wi-Fi Protected Access and IEEE 802.11i</refpurpose>
<para>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
( 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.</para>
<para>Wi-Fi Alliance ( 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&lt;TM&gt; (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
<para>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
<para>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).</para>
<para>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).</para>
<para>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).</para>
<title>IEEE 802.11i / WPA2</title>
<para>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).</para>
<title>See Also</title>
<para>wpa_supplicant is copyright (c) 2003-2012,
Jouni Malinen <email></email> and
All Rights Reserved.</para>
<para>This program is licensed under the BSD license (the one with
advertisement clause removed).</para>