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wpa_supplicant - Wi-Fi Protected Access client and IEEE 802.1X supplicant
wpa_supplicant [ -BddehLqqvw ] [ -iifname ] [ -cconfig file ] [ -Ddriver ]
Wireless networks do not require physical access to the network equipment in the same way as wired networks. This makes it easier for unauthorized users to passively monitor a network and capture all transmitted frames. In addition, unauthorized use of the network is much easier. In many cases, this can happen even without user's explicit knowledge since the wireless LAN adapter may have been configured to automatically join any available network.
Link-layer encryption can be used to provide a layer of security for wireless networks. The original wireless LAN standard, IEEE 802.11, included a simple encryption mechanism, WEP. However, that proved to be flawed in many areas and network protected with WEP cannot be consider secure. IEEE 802.1X authentication and frequently changed dynamic WEP keys can be used to improve the network security, but even that has inherited security issues due to the use of WEP for encryption. Wi-Fi Protected Access and IEEE 802.11i amendment to the wireless LAN standard introduce a much improvement mechanism for securing wireless networks. IEEE 802.11i enabled networks that are using CCMP (encryption mechanism based on strong cryptographic algorithm AES) can finally be called secure used for applications which require efficient protection against unauthorized access.
wpa_supplicant is an implementation of the WPA Supplicant component, i.e., the part that runs in the client stations. It implements WPA key negotiation with a WPA Authenticator and EAP authentication with Authentication Server. In addition, it controls the roaming and IEEE 802.11 authentication/association of the wireless LAN driver.
wpa_supplicant is designed to be a "daemon" program that runs in the background and acts as the backend component controlling the wireless connection. wpa_supplicant supports separate frontend programs and an example text-based frontend, wpa_cli, is included with wpa_supplicant.
Before wpa_supplicant can do its work, the network interface must be available. That means that the physical device must be present and enabled, and the driver for the device must have be loaded. Note, however, that the '-w' option of the wpa_supplicant daemon instructs the daemon to continue running and to wait for the interface to become available. Without the '-w' option, the daemon will exit immediately if the device is not already available.
After wpa_supplicant has configured the network device, higher level configuration such as DHCP may proceed. There are a variety of ways to integrate wpa_supplicant into a machine's networking scripts, a few of which are described in sections below.
The following steps are used when associating with an AP using WPA:
Supported WPA/IEEE 802.11i features:
The available drivers to specify with the -D option are:
In most common cases, wpa_supplicant is started with:
wpa_supplicant -Bw -c/etc/wpa_supplicant.conf -iwlan0
This makes the process fork into background and wait for the wlan0 interface if it is not available at startup time.
The easiest way to debug problems, and to get debug log for bug reports, is to start wpa_supplicant on foreground with debugging enabled:
wpa_supplicant -c/etc/wpa_supplicant.conf -iwlan0 -d
wpa_supplicant can control multiple interfaces (radios) either by running one process for each interface separately or by running just one process and list of options at command line. Each interface is separated with -N argument. As an example, following command would start wpa_supplicant for two interfaces:
wpa_supplicant \
-c wpa1.conf -i wlan0 -D hostap -N \
-c wpa2.conf -i ath0 -D madwifi
Current hardware/software requirements:
wpa_supplicant was designed to be portable for different drivers and operating systems. Hopefully, support for more wlan cards and OSes will be added in the future. See developer.txt for more information about the design of wpa_supplicant and porting to other drivers. One main goal is to add full WPA/WPA2 support to Linux wireless extensions to allow new drivers to be supported without having to implement new driver-specific interface code in wpa_supplicant.
The wpa_supplicant system consists of the following components:
First, make a configuration file, e.g. /etc/wpa_supplicant.conf, that describes the networks you are interested in. See wpa_supplicant(5) for details.
Once the configuration is ready, you can test whether the configuration works by running wpa_supplicant with following command to start it on foreground with debugging enabled:
wpa_supplicant -iwlan0 -c/etc/wpa_supplicant.conf -d
Assuming everything goes fine, you can start using following command to start wpa_supplicant on background without debugging:
wpa_supplicant -iwlan0 -c/etc/wpa_supplicant.conf -B
Please note that if you included more than one driver interface in the build time configuration (.config), you may need to specify which interface to use by including -D<driver name> option on the command line.
For example, following small changes to pcmcia-cs scripts can be used to enable WPA support:
Add MODE="Managed" and WPA="y" to the network scheme in /etc/pcmcia/wireless.opts.
Add the following block to the end of 'start' action handler in /etc/pcmcia/wireless:
if [ "$WPA" = "y" -a -x /usr/local/bin/wpa_supplicant ]; then
/usr/local/bin/wpa_supplicant -Bw -c/etc/wpa_supplicant.conf -i$DEVICE
fi
Add the following block to the end of 'stop' action handler (may need to be separated from other actions) in /etc/pcmcia/wireless:
if [ "$WPA" = "y" -a -x /usr/local/bin/wpa_supplicant ]; then
killall wpa_supplicant
fi
This will make cardmgr start wpa_supplicant when the card is plugged in. wpa_supplicant will wait until the interface is set up--either when a static IP address is configured or when DHCP client is started--and will then negotiate keys with the AP.
wpa_background(8) wpa_supplicant.conf(5) wpa_cli(8) wpa_passphrase(8)
wpa_supplicant is copyright (c) 2003-2005, Jouni Malinen <jkmaline@cc.hut.fi> and contributors. All Rights Reserved.
This program is dual-licensed under both the GPL version 2 and BSD license. Either license may be used at your option.
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