130 lines
4.7 KiB
Text
130 lines
4.7 KiB
Text
wpa_supplicant and Wi-Fi Protected Setup (WPS)
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==============================================
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This document describes how the WPS implementation in wpa_supplicant
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can be configured and how an external component on the client (e.g.,
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management GUI) is used to enable WPS enrollment and registrar
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registration.
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Introduction to WPS
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-------------------
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Wi-Fi Protected Setup (WPS) is a mechanism for easy configuration of a
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wireless network. It allows automated generation of random keys (WPA
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passphrase/PSK) and configuration of an access point and client
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devices. WPS includes number of methods for setting up connections
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with PIN method and push-button configuration (PBC) being the most
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commonly deployed options.
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While WPS can enable more home networks to use encryption in the
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wireless network, it should be noted that the use of the PIN and
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especially PBC mechanisms for authenticating the initial key setup is
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not very secure. As such, use of WPS may not be suitable for
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environments that require secure network access without chance for
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allowing outsiders to gain access during the setup phase.
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WPS uses following terms to describe the entities participating in the
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network setup:
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- access point: the WLAN access point
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- Registrar: a device that control a network and can authorize
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addition of new devices); this may be either in the AP ("internal
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Registrar") or in an external device, e.g., a laptop, ("external
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Registrar")
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- Enrollee: a device that is being authorized to use the network
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It should also be noted that the AP and a client device may change
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roles (i.e., AP acts as an Enrollee and client device as a Registrar)
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when WPS is used to configure the access point.
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More information about WPS is available from Wi-Fi Alliance:
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http://www.wi-fi.org/wifi-protected-setup
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wpa_supplicant implementation
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-----------------------------
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wpa_supplicant includes an optional WPS component that can be used as
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an Enrollee to enroll new network credential or as a Registrar to
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configure an AP. The current version of wpa_supplicant does not
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support operation as an external WLAN Management Registrar for adding
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new client devices or configuring the AP over UPnP.
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wpa_supplicant configuration
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----------------------------
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WPS is an optional component that needs to be enabled in
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wpa_supplicant build configuration (.config). Here is an example
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configuration that includes WPS support and Linux wireless extensions
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-based driver interface:
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CONFIG_DRIVER_WEXT=y
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CONFIG_EAP=y
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CONFIG_WPS=y
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WPS needs the Universally Unique IDentifier (UUID; see RFC 4122) for
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the device. This is configured in the runtime configuration for
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wpa_supplicant:
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# example UUID for WPS
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uuid=12345678-9abc-def0-1234-56789abcdef0
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The network configuration blocks needed for WPS are added
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automatically based on control interface commands, so they do not need
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to be added explicitly in the configuration file.
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External operations
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-------------------
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WPS requires either a device PIN code (usually, 8-digit number) or a
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pushbutton event (for PBC) to allow a new WPS Enrollee to join the
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network. wpa_supplicant uses the control interface as an input channel
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for these events.
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If the client device has a display, a random PIN has to be generated
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for each WPS registration session. wpa_supplicant can do this with a
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control interface request, e.g., by calling wpa_cli:
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wpa_cli wps_pin any
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This will return the generated 8-digit PIN which will then need to be
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entered at the Registrar to complete WPS registration. At that point,
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the client will be enrolled with credentials needed to connect to the
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AP to access the network.
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If the client device does not have a display that could show the
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random PIN, a hardcoded PIN that is printed on a label can be
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used. wpa_supplicant is notified this with a control interface
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request, e.g., by calling wpa_cli:
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wpa_cli wps_pin any 12345670
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This starts the WPS negotiation in the same way as above with the
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generated PIN.
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If the client design wants to support optional WPS PBC mode, this can
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be enabled by either a physical button in the client device or a
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virtual button in the user interface. The PBC operation requires that
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a button is also pressed at the AP/Registrar at about the same time (2
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minute window). wpa_supplicant is notified of the local button event
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over the control interface, e.g., by calling wpa_cli:
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wpa_cli wps_pbc
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At this point, the AP/Registrar has two minutes to complete WPS
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negotiation which will generate a new WPA PSK in the same way as the
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PIN method described above.
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If the client wants to operation in the Registrar role to configure an
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AP, wpa_supplicant is notified over the control interface, e.g., with
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wpa_cli:
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wpa_cli wps_reg <AP BSSID> <AP PIN>
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(example: wpa_cli wps_reg 02:34:56:78:9a:bc 12345670)
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