101 lines
4.4 KiB
Text
101 lines
4.4 KiB
Text
<!doctype refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN">
|
|
|
|
<refentry>
|
|
<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<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).</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) 2003-2012,
|
|
Jouni Malinen <email>j@w1.fi</email> and
|
|
contributors.
|
|
All Rights Reserved.</para>
|
|
|
|
<para>This program is licensed under the BSD license (the one with
|
|
advertisement clause removed).</para>
|
|
</refsect1>
|
|
</refentry>
|