Wi-Fi Protected Access client and IEEE 802.1X supplicant
wpa_supplicant [-BhKLNptuvW] [-b br_ifname] [-C ctrl_interface] [-c config file] [-d[d]] [-f output_file] [-g global ctrl_interface] [-i ifname] [-P file] [-q[q]]
Most command-line options have global scope. Some are given per interface, and are valid only if you've specified at least one -i option; otherwise they're ignored. Option groups for different interfaces must be separated by an -N option.
- Run as a daemon in the background.
- -b br_ifname
- Optional bridge interface name. (Per interface)
- -C ctrl_interface
- The path to the ctrl_interface socket. (Per interface; used only if -c is not).
- -c filename
- Path to configuration file. (Per interface)
- Increase debugging verbosity (specify -dd for even more).
- Send the output to the specified file, instead of to standard output.
- -g global ctrl_interface
- The path to the global ctrl_interface socket. If you specify this option, you can omit the interface definitions.
- Help; display a usage message.
- -i ifname
- The interface to listen on. Multiple instances of this option can be present, one per interface, separated by an -N option (see below).
- Include keys (passwords, etc.) in the debugging output.
- Show the license (GPL and BSD).
- Start describing a new interface.
- -P file
- Specify the location of the PID file.
- Driver parameters. (Per interface)
- Decrease debugging verbosity (specify -qq for even less).
- Include the timestamp in debugging messages.
- Enable the DBus control interface. If you specify this option, you can omit the interface definitions.
- Show version information.
- Wait for a control interface before starting.
Wireless networks don't 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 the user's explicit knowledge, because 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 networks protected with WEP cannot be considered to be 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-improved mechanism for securing wireless networks. IEEE 802.11i-enabled networks that are using CCMP (an encryption mechanism based on strong cryptographic algorithm AES) can finally be called secure used for applications which require efficient protection against unauthorized access.
The wpa_supplicant utility 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.
The wpa_supplicant utility is designed to be a daemon that runs in the background and acts as the backend component controlling the wireless connection. It supports separate front-end programs and a sample text-based front-end, 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 been loaded. The daemon exits immediately if the device isn't already available.
After wpa_supplicant has configured the network device, higher-level configuration such as DHCP may proceed. There's a variety of ways to integrate wpa_supplicant into a machine's networking scripts, a few of which are described in the sections below.
The following steps are used when associating with an AP using WPA:
- wpa_supplicant requests the driver to scan neighboring BSSs.
- wpa_supplicant selects a BSS based on its configuration.
- wpa_supplicant requests the driver to associate with the chosen BSS.
- If WPA-EAP: integrated IEEE 802.1X Supplicant or external Xsupplicant completes EAP authentication with the authentication server (proxied by the Authenticator in the AP).
- If WPA-EAP: the master key is received from the IEEE 802.1X Supplicant.
- If WPA-PSK: wpa_supplicant uses PSK as the master session key.
- wpa_supplicant completes WPA 4-Way Handshake and Group Key Handshake with the Authenticator (AP).
- wpa_supplicant configures encryption keys for unicast and broadcast.
- Normal data packets can be transmitted and received.
Supported WPA/IEEE 802.11i features:
- WPA-PSK (WPA-Personal)
- WPA with EAP (e.g., with RADIUS authentication server)
The following authentication methods are supported with an integrated
IEEE 802.1X Supplicant:
- EAP-PEAP/MSCHAPv2 (both PEAPv0 and PEAPv1)
- EAP-PEAP/TLS (both PEAPv0 and PEAPv1)
- EAP-PEAP/GTC (both PEAPv0 and PEAPv1)
- EAP-PEAP/OTP (both PEAPv0 and PEAPv1)
- EAP-PEAP/MD5-Challenge (both PEAPv0 and PEAPv1)
- LEAP (note: requires special support from the driver for IEEE 802.11 authentication)
The following methods are supported, but since they don't generate keying material, they can't be used with WPA or IEEE 802.1X WEP keying:
- key management for CCMP, TKIP, WEP104, WEP40
- RSN/WPA2 (IEEE 802.11i)
- PMKSA caching
The wpa_supplicant requires the following libraries and binaries be present:
- libcrypto.so — crypto library
- libssl.so — Secure Socket Library (created from OpenSSL)
- random — executable that creates /dev/urandom for random-number generation
- libm.so — math library required by random
- libz.so — compression library required by random
The wpa_supplicant also needs a read/write filesystem for creation of a ctrl_interface directory (see the sample wpa_supplicant.conf configuration file).