1 <!doctype refentry PUBLIC "-//OASIS//DTD DocBook V4.1//EN"> 2 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<TM> (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) 2003-2012, 94 Jouni Malinen <email>j (a] w1.fi</email> and 95 contributors. 96 All Rights Reserved.</para> 97 98 <para>This program is licensed under the BSD license (the one with 99 advertisement clause removed).</para> 100 </refsect1> 101 </refentry> 102
