wpa_supplicant/doc/docbook/wpa_background.sgml

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   3 <refentry>
   4   <refmeta>
   5     <refentrytitle>wpa_background</refentrytitle>
   6     <manvolnum>8</manvolnum>
   7   </refmeta>
   8   <refnamediv>
   9     <refname>wpa_background</refname>
  10     <refpurpose>Background information on Wi-Fi Protected Access and IEEE 802.11i</refpurpose>
  11   </refnamediv>
  12   <refsect1>
  13     <title>WPA</title>
  14
  15     <para>The original security mechanism of IEEE 802.11 standard was
  16     not designed to be strong and has proven to be insufficient for
  17     most networks that require some kind of security. Task group I
  18     (Security) of IEEE 802.11 working group
  19     (http://www.ieee802.org/11/) has worked to address the flaws of
  20     the base standard and has in practice completed its work in May
  21     2004. The IEEE 802.11i amendment to the IEEE 802.11 standard was
  22     approved in June 2004 and published in July 2004.</para>
  23
  24     <para>Wi-Fi Alliance (http://www.wi-fi.org/) used a draft version
  25     of the IEEE 802.11i work (draft 3.0) to define a subset of the
  26     security enhancements that can be implemented with existing wlan
  27     hardware. This is called Wi-Fi Protected Access&lt;TM&gt; (WPA). This
  28     has now become a mandatory component of interoperability testing
  29     and certification done by Wi-Fi Alliance. Wi-Fi provides
  30     information about WPA at its web site
  31     (http://www.wi-fi.org/OpenSection/protected_access.asp).</para>
  32
  33     <para>IEEE 802.11 standard defined wired equivalent privacy (WEP)
  34     algorithm for protecting wireless networks. WEP uses RC4 with
  35     40-bit keys, 24-bit initialization vector (IV), and CRC32 to
  36     protect against packet forgery. All these choices have proven to
  37     be insufficient: key space is too small against current attacks,
  38     RC4 key scheduling is insufficient (beginning of the pseudorandom
  39     stream should be skipped), IV space is too small and IV reuse
  40     makes attacks easier, there is no replay protection, and non-keyed
  41     authentication does not protect against bit flipping packet
  42     data.</para>
  43
  44     <para>WPA is an intermediate solution for the security issues. It
  45     uses Temporal Key Integrity Protocol (TKIP) to replace WEP. TKIP
  46     is a compromise on strong security and possibility to use existing
  47     hardware. It still uses RC4 for the encryption like WEP, but with
  48     per-packet RC4 keys. In addition, it implements replay protection,
  49     keyed packet authentication mechanism (Michael MIC).</para>
  50
  51     <para>Keys can be managed using two different mechanisms. WPA can
  52     either use an external authentication server (e.g., RADIUS) and
  53     EAP just like IEEE 802.1X is using or pre-shared keys without need
  54     for additional servers. Wi-Fi calls these "WPA-Enterprise" and
  55     "WPA-Personal", respectively. Both mechanisms will generate a
  56     master session key for the Authenticator (AP) and Supplicant
  57     (client station).</para>
  58
  59     <para>WPA implements a new key handshake (4-Way Handshake and
  60     Group Key Handshake) for generating and exchanging data encryption
  61     keys between the Authenticator and Supplicant. This handshake is
  62     also used to verify that both Authenticator and Supplicant know
  63     the master session key. These handshakes are identical regardless
  64     of the selected key management mechanism (only the method for
  65     generating master session key changes).</para>
  66   </refsect1>
  67
  68   <refsect1>
  69     <title>IEEE 802.11i / WPA2</title>
  70
  71     <para>The design for parts of IEEE 802.11i that were not included
  72     in WPA has finished (May 2004) and this amendment to IEEE 802.11
  73     was approved in June 2004. Wi-Fi Alliance is using the final IEEE
  74     802.11i as a new version of WPA called WPA2. This includes, e.g.,
  75     support for more robust encryption algorithm (CCMP: AES in Counter
  76     mode with CBC-MAC) to replace TKIP and optimizations for handoff
  77     (reduced number of messages in initial key handshake,
  78     pre-authentication, and PMKSA caching).</para>
  79   </refsect1>
  80
  81   <refsect1>
  82     <title>See Also</title>
  83     <para>
  84       <citerefentry>
  85         <refentrytitle>wpa_supplicant</refentrytitle>
  86         <manvolnum>8</manvolnum>
  87       </citerefentry>
  88     </para>
  89   </refsect1>
  90
  91   <refsect1>
  92     <title>Legal</title>
  93     <para>wpa_supplicant is copyright (c) 2003-2007,
  94     Jouni Malinen <email>j@w1.fi</email> and
  95     contributors.
  96     All Rights Reserved.</para>
  97
  98     <para>This program is dual-licensed under both the GPL version 2
  99     and BSD license. Either license may be used at your option.</para>
 100   </refsect1>
 101 </refentry>