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authorJouni Malinen <j@w1.fi>2008-02-28 01:34:43 (GMT)
committerJouni Malinen <jm@jm.kir.nu>2008-02-28 01:34:43 (GMT)
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+<!doctype refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN">
+ <refmeta>
+ <refentrytitle>wpa_background</refentrytitle>
+ <manvolnum>8</manvolnum>
+ </refmeta>
+ <refnamediv>
+ <refname>wpa_background</refname>
+ <refpurpose>Background information on Wi-Fi Protected Access and IEEE 802.11i</refpurpose>
+ </refnamediv>
+ <refsect1>
+ <title>WPA</title>
+ <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
+ (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.</para>
+ <para>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&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
+ (http://www.wi-fi.org/OpenSection/protected_access.asp).</para>
+ <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
+ data.</para>
+ <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>
+ </refsect1>
+ <refsect1>
+ <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>
+ </refsect1>
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry>
+ <refentrytitle>wpa_supplicant</refentrytitle>
+ <manvolnum>8</manvolnum>
+ </citerefentry>
+ </para>
+ </refsect1>
+ <refsect1>
+ <title>Legal</title>
+ <para>wpa_supplicant is copyright (c) 2003-2007,
+ Jouni Malinen <email>j@w1.fi</email> and
+ contributors.
+ All Rights Reserved.</para>
+ <para>This program is dual-licensed under both the GPL version 2
+ and BSD license. Either license may be used at your option.</para>
+ </refsect1>