wpa_supplicant and Wi-Fi Protected Setup (WPS)
==============================================
This document describes how the WPS implementation in wpa_supplicant
can be configured and how an external component on the client (e.g.,
management GUI) is used to enable WPS enrollment and registrar
registration.
Introduction to WPS
-------------------
Wi-Fi Protected Setup (WPS) is a mechanism for easy configuration of a
wireless network. It allows automated generation of random keys (WPA
passphrase/PSK) and configuration of an access point and client
devices. WPS includes number of methods for setting up connections
with PIN method and push-button configuration (PBC) being the most
commonly deployed options.
While WPS can enable more home networks to use encryption in the
wireless network, it should be noted that the use of the PIN and
especially PBC mechanisms for authenticating the initial key setup is
not very secure. As such, use of WPS may not be suitable for
environments that require secure network access without chance for
allowing outsiders to gain access during the setup phase.
WPS uses following terms to describe the entities participating in the
network setup:
- access point: the WLAN access point
- Registrar: a device that control a network and can authorize
addition of new devices); this may be either in the AP ("internal
Registrar") or in an external device, e.g., a laptop, ("external
Registrar")
- Enrollee: a device that is being authorized to use the network
It should also be noted that the AP and a client device may change
roles (i.e., AP acts as an Enrollee and client device as a Registrar)
when WPS is used to configure the access point.
More information about WPS is available from Wi-Fi Alliance:
http://www.wi-fi.org/wifi-protected-setup
wpa_supplicant implementation
-----------------------------
wpa_supplicant includes an optional WPS component that can be used as
an Enrollee to enroll new network credential or as a Registrar to
configure an AP.
wpa_supplicant configuration
----------------------------
WPS is an optional component that needs to be enabled in
wpa_supplicant build configuration (.config). Here is an example
configuration that includes WPS support and Linux nl80211 -based
driver interface:
CONFIG_DRIVER_NL80211=y
CONFIG_WPS=y
CONFIG_WPS2=y
If you want to enable WPS external registrar (ER) functionality, you
will also need to add following line:
CONFIG_WPS_ER=y
Following parameter can be used to enable support for NFC config method:
CONFIG_WPS_NFC=y
WPS needs the Universally Unique IDentifier (UUID; see RFC 4122) for
the device. This is configured in the runtime configuration for
wpa_supplicant (if not set, UUID will be generated based on local MAC
address):
# example UUID for WPS
uuid=12345678-9abc-def0-1234-56789abcdef0
The network configuration blocks needed for WPS are added
automatically based on control interface commands, so they do not need
to be added explicitly in the configuration file.
WPS registration will generate new network blocks for the acquired
credentials. If these are to be stored for future use (after
restarting wpa_supplicant), wpa_supplicant will need to be configured
to allow configuration file updates:
update_config=1
External operations
-------------------
WPS requires either a device PIN code (usually, 8-digit number) or a
pushbutton event (for PBC) to allow a new WPS Enrollee to join the
network. wpa_supplicant uses the control interface as an input channel
for these events.
The PIN value used in the commands must be processed by an UI to
remove non-digit characters and potentially, to verify the checksum
digit. "wpa_cli wps_check_pin <PIN>" can be used to do such processing.
It returns FAIL if the PIN is invalid, or FAIL-CHECKSUM if the checksum
digit is incorrect, or the processed PIN (non-digit characters removed)
if the PIN is valid.
If the client device has a display, a random PIN has to be generated
for each WPS registration session. wpa_supplicant can do this with a
control interface request, e.g., by calling wpa_cli:
wpa_cli wps_pin any
This will return the generated 8-digit PIN which will then need to be
entered at the Registrar to complete WPS registration. At that point,
the client will be enrolled with credentials needed to connect to the
AP to access the network.
If the client device does not have a display that could show the
random PIN, a hardcoded PIN that is printed on a label can be
used. wpa_supplicant is notified this with a control interface
request, e.g., by calling wpa_cli:
wpa_cli wps_pin any 12345670
This starts the WPS negotiation in the same way as above with the
generated PIN.
When the wps_pin command is issued for an AP (including P2P GO) mode
interface, an optional timeout parameter can be used to specify
expiration timeout for the PIN in seconds. For example:
wpa_cli wps_pin any 12345670 300
If a random PIN is needed for a user interface, "wpa_cli wps_pin get"
can be used to generate a new PIN without starting WPS negotiation.
This random PIN can then be passed as an argument to another wps_pin
call when the actual operation should be started.
If the client design wants to support optional WPS PBC mode, this can
be enabled by either a physical button in the client device or a
virtual button in the user interface. The PBC operation requires that
a button is also pressed at the AP/Registrar at about the same time (2
minute window). wpa_supplicant is notified of the local button event
over the control interface, e.g., by calling wpa_cli:
wpa_cli wps_pbc
At this point, the AP/Registrar has two minutes to complete WPS
negotiation which will generate a new WPA PSK in the same way as the
PIN method described above.
If the client wants to operate in the Registrar role to learn the
current AP configuration and optionally, to configure an AP,
wpa_supplicant is notified over the control interface, e.g., with
wpa_cli:
wpa_cli wps_reg <AP BSSID> <AP PIN>
(example: wpa_cli wps_reg 02:34:56:78:9a:bc 12345670)
This is used to fetch the current AP settings instead of actually
changing them. The main difference with the wps_pin command is that
wps_reg uses the AP PIN (e.g., from a label on the AP) instead of a
PIN generated at the client.
In order to change the AP configuration, the new configuration
parameters are given to the wps_reg command:
wpa_cli wps_reg <AP BSSID> <AP PIN> <new SSID> <auth> <encr> <new key>
examples:
wpa_cli wps_reg 02:34:56:78:9a:bc 12345670 testing WPA2PSK CCMP 12345678
wpa_cli wps_reg 02:34:56:78:9a:bc 12345670 clear OPEN NONE ""
<auth> must be one of the following: OPEN WPAPSK WPA2PSK
<encr> must be one of the following: NONE WEP TKIP CCMP
Scanning
--------
Scan results ('wpa_cli scan_results' or 'wpa_cli bss <idx>') include a
flags field that is used to indicate whether the BSS support WPS. If
the AP support WPS, but has not recently activated a Registrar, [WPS]
flag will be included. If PIN method has been recently selected,
[WPS-PIN] is shown instead. Similarly, [WPS-PBC] is shown if PBC mode
is in progress. GUI programs can use these as triggers for suggesting
a guided WPS configuration to the user. In addition, control interface
monitor events WPS-AP-AVAILABLE{,-PBC,-PIN} can be used to find out if
there are WPS enabled APs in scan results without having to go through
all the details in the GUI. These notification could be used, e.g., to
suggest possible WPS connection to the user.
wpa_gui
-------
wpa_gui-qt4 directory contains a sample GUI that shows an example of
how WPS support can be integrated into the GUI. Its main window has a
WPS tab that guides user through WPS registration with automatic AP
selection. In addition, it shows how WPS can be started manually by
selecting an AP from scan results.
Credential processing
---------------------
By default, wpa_supplicant processes received credentials and updates
its configuration internally. However, it is possible to
control these operations from external programs, if desired.
This internal processing can be disabled with wps_cred_processing=1
option. When this is used, an external program is responsible for
processing the credential attributes and updating wpa_supplicant
configuration based on them.
Following control interface messages are sent out for external programs:
WPS-CRED-RECEIVED <hexdump of Credential attribute(s)>
For example:
<2>WPS-CRED-RECEIVED 100e006f10260001011045000c6a6b6d2d7770732d74657374100300020020100f000200081027004030653462303435366332363666653064333961643135353461316634626637313234333761636664623766333939653534663166316230323061643434386235102000060266a0ee1727
wpa_supplicant as WPS External Registrar (ER)
---------------------------------------------
wpa_supplicant can be used as a WPS ER to configure an AP or enroll
new Enrollee to join the network. This functionality uses UPnP and
requires that a working IP connectivity is available with the AP (this
can be either over a wired or wireless connection).
Separate wpa_supplicant process can be started for WPS ER
operations. A special "none" driver can be used in such a case to
indicate that no local network interface is actually controlled. For
example, following command could be used to start the ER:
wpa_supplicant -Dnone -c er.conf -ieth0
Sample er.conf:
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=admin
device_name=WPS External Registrar
wpa_cli commands for ER functionality:
wps_er_start [IP address]
- start WPS ER functionality
- the optional IP address parameter can be used to filter operations only
to include a single AP
- if run again while ER is active, the stored information (discovered APs
and Enrollees) are shown again
wps_er_stop
- stop WPS ER functionality
wps_er_learn <UUID|BSSID> <AP PIN>
- learn AP configuration
wps_er_set_config <UUID|BSSID> <network id>
- use AP configuration from a locally configured network (e.g., from
wps_reg command); this does not change the AP's configuration, but
only prepares a configuration to be used when enrolling a new device
to the AP
wps_er_config <UUID|BSSID> <AP PIN> <new SSID> <auth> <encr> <new key>
- examples:
wps_er_config 87654321-9abc-def0-1234-56789abc0002 12345670 testing WPA2PSK CCMP 12345678
wpa_er_config 87654321-9abc-def0-1234-56789abc0002 12345670 clear OPEN NONE ""
<auth> must be one of the following: OPEN WPAPSK WPA2PSK
<encr> must be one of the following: NONE WEP TKIP CCMP
wps_er_pbc <Enrollee UUID|MAC address>
- accept an Enrollee PBC using External Registrar
wps_er_pin <Enrollee UUID|"any"|MAC address> <PIN> [Enrollee MAC address]
- add an Enrollee PIN to External Registrar
- if Enrollee UUID is not known, "any" can be used to add a wildcard PIN
- if the MAC address of the enrollee is known, it should be configured
to allow the AP to advertise list of authorized enrollees
WPS ER events:
WPS_EVENT_ER_AP_ADD
- WPS ER discovered an AP
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/
WPS_EVENT_ER_AP_REMOVE
- WPS ER removed an AP entry
WPS-ER-AP-REMOVE 87654321-9abc-def0-1234-56789abc0002
WPS_EVENT_ER_ENROLLEE_ADD
- WPS ER discovered a new Enrollee
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|
WPS_EVENT_ER_ENROLLEE_REMOVE
- WPS ER removed an Enrollee entry
WPS-ER-ENROLLEE-REMOVE 2b7093f1-d6fb-5108-adbb-bea66bb87333 02:66:a0:ee:17:27
WPS-ER-AP-SETTINGS
- WPS ER learned AP settings
WPS-ER-AP-SETTINGS uuid=fd91b4ec-e3fa-5891-a57d-8c59efeed1d2 ssid=test-wps auth_type=0x0020 encr_type=0x0008 key=12345678
WPS with NFC
------------
WPS can be used with NFC-based configuration method. An NFC tag
containing a password token from the Enrollee can be used to
authenticate the connection instead of the PIN. In addition, an NFC tag
with a configuration token can be used to transfer AP settings without
going through the WPS protocol.
When the station acts as an Enrollee, a local NFC tag with a password
token can be used by touching the NFC interface of a Registrar.
"wps_nfc [BSSID]" command starts WPS protocol run with the local end as
the Enrollee using the NFC password token that is either pre-configured
in the configuration file (wps_nfc_dev_pw_id, wps_nfc_dh_pubkey,
wps_nfc_dh_privkey, wps_nfc_dev_pw) or generated dynamically with
"wps_nfc_token <WPS|NDEF>" command. The included nfc_pw_token tool
(build with "make nfc_pw_token") can be used to generate NFC password
tokens during manufacturing (each station needs to have its own random
keys).
The "wps_nfc_config_token <WPS/NDEF>" command can be used to build an
NFC configuration token when wpa_supplicant is controlling an AP
interface (AP or P2P GO). The output value from this command is a
hexdump of the current AP configuration (WPS parameter requests this to
include only the WPS attributes; NDEF parameter requests additional NDEF
encapsulation to be included). This data needs to be written to an NFC
tag with an external program. Once written, the NFC configuration token
can be used to touch an NFC interface on a station to provision the
credentials needed to access the network.
The "wps_nfc_config_token <WPS/NDEF> <network id>" command can be used
to build an NFC configuration token based on a locally configured
network.
If the station includes NFC interface and reads an NFC tag with a MIME
media type "application/vnd.wfa.wsc", the NDEF message payload (with or
without NDEF encapsulation) can be delivered to wpa_supplicant using the
following wpa_cli command:
wps_nfc_tag_read <hexdump of payload>
If the NFC tag contains a configuration token, the network is added to
wpa_supplicant configuration. If the NFC tag contains a password token,
the token is added to the WPS Registrar component. This information can
then be used with wps_reg command (when the NFC password token was from
an AP) using a special value "nfc-pw" in place of the PIN parameter. If
the ER functionality has been started (wps_er_start), the NFC password
token is used to enable enrollment of a new station (that was the source
of the NFC password token).
"nfc_get_handover_req <NDEF> <WPS>" command can be used to build the
contents of a Handover Request Message for connection handover. The
first argument selects the format of the output data and the second
argument selects which type of connection handover is requested (WPS =
Wi-Fi handover as specified in WSC 2.0).
"nfc_get_handover_sel <NDEF> <WPS> [UUID|BSSID]" command can be used to
build the contents of a Handover Select Message for connection handover
when this does not depend on the contents of the Handover Request
Message. The first argument selects the format of the output data and
the second argument selects which type of connection handover is
requested (WPS = Wi-Fi handover as specified in WSC 2.0). If the options
UUID|BSSID argument is included, this is a request to build the handover
message for the specified AP when wpa_supplicant is operating as a WPS
ER.
"nfc_rx_handover_req <hexdump of payload>" is used to indicate receipt
of NFC connection handover request. The payload may include multiple
carriers the the applicable ones are matched based on the media
type. The reply data is contents for the Handover Select Message
(hexdump).
"nfc_rx_handover_sel <hexdump of payload>" is used to indicate receipt
of NFC connection handover select. The payload may include multiple
carriers the the applicable ones are matched based on the media
type.
"nfc_report_handover <INIT/RESP> WPS <carrier from handover request>
<carrier from handover select>" can be used as an alternative way for
reporting completed NFC connection handover. The first parameter
indicates whether the local device initiated or responded to the
connection handover and the carrier records are the selected carrier
from the handover request and select messages as a hexdump.
The "wps_er_nfc_config_token <WPS/NDEF> <UUID|BSSID>" command can be
used to build an NFC configuration token for the specified AP when
wpa_supplicant is operating as a WPS ER. The output value from this
command is a hexdump of the selected AP configuration (WPS parameter
requests this to include only the WPS attributes; NDEF parameter
requests additional NDEF encapsulation to be included). This data needs
to be written to an NFC tag with an external program. Once written, the
NFC configuration token can be used to touch an NFC interface on a
station to provision the credentials needed to access the network.