1WPA_BACKGROUND(8) WPA_BACKGROUND(8)
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6 wpa_background - Background information on Wi-Fi Protected Access and
7 IEEE 802.11i
8
10 The original security mechanism of IEEE 802.11 standard was not
11 designed to be strong and has proven to be insufficient for most net‐
12 works that require some kind of security. Task group I (Security) of
13 IEEE 802.11 working group (http://www.ieee802.org/11/) has worked to
14 address the flaws of the base standard and has in practice completed
15 its work in May 2004. The IEEE 802.11i amendment to the IEEE 802.11
16 standard was approved in June 2004 and published in July 2004.
17 Wi-Fi Alliance (http://www.wi-fi.org/) used a draft version of the IEEE
19 802.11i work (draft 3.0) to define a subset of the security enhance‐
20 ments that can be implemented with existing wlan hardware. This is
21 called Wi-Fi Protected Access<TM> (WPA). This has now become a manda‐
22 tory component of interoperability testing and certification done by
23 Wi-Fi Alliance. Wi-Fi provides information about WPA at its web site
24 (http://www.wi-fi.org/OpenSection/protected_access.asp).
25 IEEE 802.11 standard defined wired equivalent privacy (WEP) algorithm
27 for protecting wireless networks. WEP uses RC4 with 40-bit keys, 24-bit
28 initialization vector (IV), and CRC32 to protect against packet
29 forgery. All these choices have proven to be insufficient: key space is
30 too small against current attacks, RC4 key scheduling is insufficient
31 (beginning of the pseudorandom stream should be skipped), IV space is
32 too small and IV reuse makes attacks easier, there is no replay protec‐
33 tion, and non-keyed authentication does not protect against bit flip‐
34 ping packet data.
35 WPA is an intermediate solution for the security issues. It uses Tempo‐
37 ral Key Integrity Protocol (TKIP) to replace WEP. TKIP is a compromise
38 on strong security and possibility to use existing hardware. It still
39 uses RC4 for the encryption like WEP, but with per-packet RC4 keys. In
40 addition, it implements replay protection, keyed packet authentication
41 mechanism (Michael MIC).
42 Keys can be managed using two different mechanisms. WPA can either use
44 an external authentication server (e.g., RADIUS) and EAP just like IEEE
45 802.1X is using or pre-shared keys without need for additional servers.
46 Wi-Fi calls these "WPA-Enterprise" and "WPA-Personal", respectively.
47 Both mechanisms will generate a master session key for the Authentica‐
48 tor (AP) and Supplicant (client station).
49 WPA implements a new key handshake (4-Way Handshake and Group Key Hand‐
51 shake) for generating and exchanging data encryption keys between the
52 Authenticator and Supplicant. This handshake is also used to verify
53 that both Authenticator and Supplicant know the master session key.
54 These handshakes are identical regardless of the selected key manage‐
55 ment mechanism (only the method for generating master session key
56 changes).
57
59 The design for parts of IEEE 802.11i that were not included in WPA has
60 finished (May 2004) and this amendment to IEEE 802.11 was approved in
61 June 2004. Wi-Fi Alliance is using the final IEEE 802.11i as a new ver‐
62 sion of WPA called WPA2. This includes, e.g., support for more robust
63 encryption algorithm (CCMP: AES in Counter mode with CBC-MAC) to
64 replace TKIP and optimizations for handoff (reduced number of messages
65 in initial key handshake, pre-authentication, and PMKSA caching).
66
68 wpa_supplicant(8)
69
71 wpa_supplicant is copyright (c) 2003-2005, Jouni Malinen <jkma‐
72 line@cc.hut.fi> and contributors. All Rights Reserved.
73 This program is dual-licensed under both the GPL version 2 and BSD
75 license. Either license may be used at your option.
76 31 December 2006 WPA_BACKGROUND(8)