348 lines
13 KiB
Plaintext
348 lines
13 KiB
Plaintext
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.
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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 nl80211 -based
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driver interface:
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CONFIG_DRIVER_NL80211=y
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CONFIG_WPS=y
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CONFIG_WPS2=y
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If you want to enable WPS external registrar (ER) functionality, you
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will also need to add following line:
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CONFIG_WPS_ER=y
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Following parameter can be used to enable support for NFC config method:
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CONFIG_WPS_NFC=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 (if not set, UUID will be generated based on local MAC
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address):
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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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WPS registration will generate new network blocks for the acquired
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credentials. If these are to be stored for future use (after
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restarting wpa_supplicant), wpa_supplicant will need to be configured
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to allow configuration file updates:
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update_config=1
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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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The PIN value used in the commands must be processed by an UI to
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remove non-digit characters and potentially, to verify the checksum
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digit. "wpa_cli wps_check_pin <PIN>" can be used to do such processing.
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It returns FAIL if the PIN is invalid, or FAIL-CHECKSUM if the checksum
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digit is incorrect, or the processed PIN (non-digit characters removed)
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if the PIN is valid.
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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 a random PIN is needed for a user interface, "wpa_cli wps_pin get"
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can be used to generate a new PIN without starting WPS negotiation.
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This random PIN can then be passed as an argument to another wps_pin
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call when the actual operation should be started.
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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 operate in the Registrar role to learn the
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current AP configuration and optionally, to configure an AP,
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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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This is used to fetch the current AP settings instead of actually
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changing them. The main difference with the wps_pin command is that
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wps_reg uses the AP PIN (e.g., from a label on the AP) instead of a
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PIN generated at the client.
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In order to change the AP configuration, the new configuration
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parameters are given to the wps_reg command:
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wpa_cli wps_reg <AP BSSID> <AP PIN> <new SSID> <auth> <encr> <new key>
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examples:
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wpa_cli wps_reg 02:34:56:78:9a:bc 12345670 testing WPA2PSK CCMP 12345678
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wpa_cli wps_reg 02:34:56:78:9a:bc 12345670 clear OPEN NONE ""
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<auth> must be one of the following: OPEN WPAPSK WPA2PSK
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<encr> must be one of the following: NONE WEP TKIP CCMP
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Scanning
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--------
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Scan results ('wpa_cli scan_results' or 'wpa_cli bss <idx>') include a
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flags field that is used to indicate whether the BSS support WPS. If
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the AP support WPS, but has not recently activated a Registrar, [WPS]
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flag will be included. If PIN method has been recently selected,
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[WPS-PIN] is shown instead. Similarly, [WPS-PBC] is shown if PBC mode
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is in progress. GUI programs can use these as triggers for suggesting
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a guided WPS configuration to the user. In addition, control interface
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monitor events WPS-AP-AVAILABLE{,-PBC,-PIN} can be used to find out if
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there are WPS enabled APs in scan results without having to go through
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all the details in the GUI. These notification could be used, e.g., to
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suggest possible WPS connection to the user.
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wpa_gui
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-------
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wpa_gui-qt4 directory contains a sample GUI that shows an example of
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how WPS support can be integrated into the GUI. Its main window has a
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WPS tab that guides user through WPS registration with automatic AP
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selection. In addition, it shows how WPS can be started manually by
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selecting an AP from scan results.
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Credential processing
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---------------------
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By default, wpa_supplicant processes received credentials and updates
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its configuration internally. However, it is possible to
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control these operations from external programs, if desired.
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This internal processing can be disabled with wps_cred_processing=1
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option. When this is used, an external program is responsible for
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processing the credential attributes and updating wpa_supplicant
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configuration based on them.
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Following control interface messages are sent out for external programs:
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WPS-CRED-RECEIVED <hexdump of Credential attribute(s)>
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For example:
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<2>WPS-CRED-RECEIVED 100e006f10260001011045000c6a6b6d2d7770732d74657374100300020020100f000200081027004030653462303435366332363666653064333961643135353461316634626637313234333761636664623766333939653534663166316230323061643434386235102000060266a0ee1727
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wpa_supplicant as WPS External Registrar (ER)
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---------------------------------------------
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wpa_supplicant can be used as a WPS ER to configure an AP or enroll
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new Enrollee to join the network. This functionality uses UPnP and
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requires that a working IP connectivity is available with the AP (this
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can be either over a wired or wireless connection).
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Separate wpa_supplicant process can be started for WPS ER
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operations. A special "none" driver can be used in such a case to
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indicate that no local network interface is actually controlled. For
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example, following command could be used to start the ER:
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wpa_supplicant -Dnone -c er.conf -ieth0
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Sample er.conf:
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ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=admin
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device_name=WPS External Registrar
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wpa_cli commands for ER functionality:
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wps_er_start [IP address]
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- start WPS ER functionality
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- the optional IP address parameter can be used to filter operations only
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to include a single AP
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- if run again while ER is active, the stored information (discovered APs
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and Enrollees) are shown again
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wps_er_stop
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- stop WPS ER functionality
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wps_er_learn <UUID> <AP PIN>
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- learn AP configuration
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wps_er_set_config <UUID> <network id>
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- use AP configuration from a locally configured network (e.g., from
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wps_reg command); this does not change the AP's configuration, but
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only prepares a configuration to be used when enrolling a new device
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to the AP
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wps_er_config <UUID> <AP PIN> <new SSID> <auth> <encr> <new key>
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- examples:
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wps_er_config 87654321-9abc-def0-1234-56789abc0002 12345670 testing WPA2PSK CCMP 12345678
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wpa_er_config 87654321-9abc-def0-1234-56789abc0002 12345670 clear OPEN NONE ""
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<auth> must be one of the following: OPEN WPAPSK WPA2PSK
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<encr> must be one of the following: NONE WEP TKIP CCMP
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wps_er_pbc <Enrollee UUID>
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- accept an Enrollee PBC using External Registrar
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wps_er_pin <Enrollee UUID> <PIN> [Enrollee MAC address]
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- add an Enrollee PIN to External Registrar
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- if Enrollee UUID is not known, "any" can be used to add a wildcard PIN
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- if the MAC address of the enrollee is known, it should be configured
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to allow the AP to advertise list of authorized enrollees
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WPS ER events:
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WPS_EVENT_ER_AP_ADD
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- WPS ER discovered an AP
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WPS-ER-AP-ADD 87654321-9abc-def0-1234-56789abc0002 02:11:22:33:44:55 pri_dev_type=6-0050F204-1 wps_state=1 |Very friendly name|Company|Long description of the model|WAP|http://w1.fi/|http://w1.fi/hostapd/
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WPS_EVENT_ER_AP_REMOVE
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- WPS ER removed an AP entry
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WPS-ER-AP-REMOVE 87654321-9abc-def0-1234-56789abc0002
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WPS_EVENT_ER_ENROLLEE_ADD
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- WPS ER discovered a new Enrollee
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WPS-ER-ENROLLEE-ADD 2b7093f1-d6fb-5108-adbb-bea66bb87333 02:66:a0:ee:17:27 M1=1 config_methods=0x14d dev_passwd_id=0 pri_dev_type=1-0050F204-1 |Wireless Client|Company|cmodel|123|12345|
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WPS_EVENT_ER_ENROLLEE_REMOVE
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- WPS ER removed an Enrollee entry
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WPS-ER-ENROLLEE-REMOVE 2b7093f1-d6fb-5108-adbb-bea66bb87333 02:66:a0:ee:17:27
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WPS-ER-AP-SETTINGS
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- WPS ER learned AP settings
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WPS-ER-AP-SETTINGS uuid=fd91b4ec-e3fa-5891-a57d-8c59efeed1d2 ssid=test-wps auth_type=0x0020 encr_type=0x0008 key=12345678
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WPS with NFC
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------------
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WPS can be used with NFC-based configuration method. An NFC tag
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containing a password token from the Enrollee can be used to
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authenticate the connection instead of the PIN. In addition, an NFC tag
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with a configuration token can be used to transfer AP settings without
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going through the WPS protocol.
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When the station acts as an Enrollee, a local NFC tag with a password
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token can be used by touching the NFC interface of a Registrar.
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"wps_nfc [BSSID]" command starts WPS protocol run with the local end as
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the Enrollee using the NFC password token that is either pre-configured
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in the configuration file (wps_nfc_dev_pw_id, wps_nfc_dh_pubkey,
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wps_nfc_dh_privkey, wps_nfc_dev_pw) or generated dynamically with
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"wps_nfc_token <WPS|NDEF>" command. The included nfc_pw_token tool
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(build with "make nfc_pw_token") can be used to generate NFC password
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tokens during manufacturing (each station needs to have its own random
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keys).
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If the station includes NFC interface and reads an NFC tag with a MIME
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media type "application/vnd.wfa.wsc", the NDEF message payload (with or
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without NDEF encapsulation) can be delivered to wpa_supplicant using the
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following wpa_cli command:
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wps_nfc_tag_read <hexdump of payload>
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If the NFC tag contains a configuration token, the network is added to
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wpa_supplicant configuration. If the NFC tag contains a password token,
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the token is added to the WPS Registrar component. This information can
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then be used with wps_reg command (when the NFC password token was from
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an AP) using a special value "nfc-pw" in place of the PIN parameter. If
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the ER functionality has been started (wps_er_start), the NFC password
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token is used to enable enrollment of a new station (that was the source
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of the NFC password token).
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