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102 lines
4.4 KiB
Plaintext
102 lines
4.4 KiB
Plaintext
<!doctype refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN">
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<refentry>
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<refmeta>
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<refentrytitle>wpa_background</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>wpa_background</refname>
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<refpurpose>Background information on Wi-Fi Protected Access and IEEE 802.11i</refpurpose>
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</refnamediv>
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<refsect1>
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<title>WPA</title>
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<para>The original security mechanism of IEEE 802.11 standard was
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not designed to be strong and has proven to be insufficient for
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most networks that require some kind of security. Task group I
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(Security) of IEEE 802.11 working group
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(http://www.ieee802.org/11/) has worked to address the flaws of
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the base standard and has in practice completed its work in May
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2004. The IEEE 802.11i amendment to the IEEE 802.11 standard was
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approved in June 2004 and published in July 2004.</para>
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<para>Wi-Fi Alliance (http://www.wi-fi.org/) used a draft version
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of the IEEE 802.11i work (draft 3.0) to define a subset of the
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security enhancements that can be implemented with existing wlan
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hardware. This is called Wi-Fi Protected Access<TM> (WPA). This
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has now become a mandatory component of interoperability testing
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and certification done by Wi-Fi Alliance. Wi-Fi provides
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information about WPA at its web site
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(http://www.wi-fi.org/OpenSection/protected_access.asp).</para>
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<para>IEEE 802.11 standard defined wired equivalent privacy (WEP)
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algorithm for protecting wireless networks. WEP uses RC4 with
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40-bit keys, 24-bit initialization vector (IV), and CRC32 to
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protect against packet forgery. All these choices have proven to
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be insufficient: key space is too small against current attacks,
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RC4 key scheduling is insufficient (beginning of the pseudorandom
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stream should be skipped), IV space is too small and IV reuse
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makes attacks easier, there is no replay protection, and non-keyed
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authentication does not protect against bit flipping packet
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data.</para>
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<para>WPA is an intermediate solution for the security issues. It
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uses Temporal Key Integrity Protocol (TKIP) to replace WEP. TKIP
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is a compromise on strong security and possibility to use existing
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hardware. It still uses RC4 for the encryption like WEP, but with
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per-packet RC4 keys. In addition, it implements replay protection,
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keyed packet authentication mechanism (Michael MIC).</para>
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<para>Keys can be managed using two different mechanisms. WPA can
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either use an external authentication server (e.g., RADIUS) and
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EAP just like IEEE 802.1X is using or pre-shared keys without need
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for additional servers. Wi-Fi calls these "WPA-Enterprise" and
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"WPA-Personal", respectively. Both mechanisms will generate a
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master session key for the Authenticator (AP) and Supplicant
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(client station).</para>
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<para>WPA implements a new key handshake (4-Way Handshake and
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Group Key Handshake) for generating and exchanging data encryption
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keys between the Authenticator and Supplicant. This handshake is
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also used to verify that both Authenticator and Supplicant know
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the master session key. These handshakes are identical regardless
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of the selected key management mechanism (only the method for
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generating master session key changes).</para>
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</refsect1>
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<refsect1>
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<title>IEEE 802.11i / WPA2</title>
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<para>The design for parts of IEEE 802.11i that were not included
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in WPA has finished (May 2004) and this amendment to IEEE 802.11
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was approved in June 2004. Wi-Fi Alliance is using the final IEEE
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802.11i as a new version of WPA called WPA2. This includes, e.g.,
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support for more robust encryption algorithm (CCMP: AES in Counter
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mode with CBC-MAC) to replace TKIP and optimizations for handoff
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(reduced number of messages in initial key handshake,
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pre-authentication, and PMKSA caching).</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry>
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<refentrytitle>wpa_supplicant</refentrytitle>
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<manvolnum>8</manvolnum>
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</citerefentry>
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</para>
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</refsect1>
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<refsect1>
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<title>Legal</title>
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<para>wpa_supplicant is copyright (c) 2003-2007,
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Jouni Malinen <email>j@w1.fi</email> and
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contributors.
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All Rights Reserved.</para>
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<para>This program is dual-licensed under both the GPL version 2
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and BSD license. Either license may be used at your option.</para>
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</refsect1>
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</refentry>
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