1 hostapd and Wi-Fi Protected Setup (WPS)
2 =======================================
4 This document describes how the WPS implementation in hostapd can be
5 configured and how an external component on an AP (e.g., web UI) is
6 used to enable enrollment of client devices.
12 Wi-Fi Protected Setup (WPS) is a mechanism for easy configuration of a
13 wireless network. It allows automated generation of random keys (WPA
14 passphrase/PSK) and configuration of an access point and client
15 devices. WPS includes number of methods for setting up connections
16 with PIN method and push-button configuration (PBC) being the most
17 commonly deployed options.
19 While WPS can enable more home networks to use encryption in the
20 wireless network, it should be noted that the use of the PIN and
21 especially PBC mechanisms for authenticating the initial key setup is
22 not very secure. As such, use of WPS may not be suitable for
23 environments that require secure network access without chance for
24 allowing outsiders to gain access during the setup phase.
26 WPS uses following terms to describe the entities participating in the
28 - access point: the WLAN access point
29 - Registrar: a device that control a network and can authorize
30 addition of new devices); this may be either in the AP ("internal
31 Registrar") or in an external device, e.g., a laptop, ("external
33 - Enrollee: a device that is being authorized to use the network
35 It should also be noted that the AP and a client device may change
36 roles (i.e., AP acts as an Enrollee and client device as a Registrar)
37 when WPS is used to configure the access point.
40 More information about WPS is available from Wi-Fi Alliance:
41 http://www.wi-fi.org/wifi-protected-setup
44 hostapd implementation
45 ----------------------
47 hostapd includes an optional WPS component that can be used as an
48 internal WPS Registrar to manage addition of new WPS enabled clients
49 to the network. In addition, WPS Enrollee functionality in hostapd can
50 be used to allow external WPS Registrars to configure the access
51 point, e.g., for initial network setup. In addition, hostapd can proxy a
52 WPS registration between a wireless Enrollee and an external Registrar
53 (e.g., Microsoft Vista or Atheros JumpStart) with UPnP.
59 WPS is an optional component that needs to be enabled in hostapd build
60 configuration (.config). Here is an example configuration that
61 includes WPS support and uses nl80211 driver interface:
63 CONFIG_DRIVER_NL80211=y
67 Following parameter can be used to enable support for NFC config method:
72 Following section shows an example runtime configuration
73 (hostapd.conf) that enables WPS:
75 # Configure the driver and network interface
79 # WPA2-Personal configuration for the AP
84 # Default WPA passphrase for legacy (non-WPS) clients
85 wpa_passphrase=12345678
86 # Enable random per-device PSK generation for WPS clients
87 # Please note that the file has to exists for hostapd to start (i.e., create an
88 # empty file as a starting point).
89 wpa_psk_file=/etc/hostapd.psk
91 # Enable control interface for PBC/PIN entry
92 ctrl_interface=/var/run/hostapd
94 # Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup)
97 # WPS configuration (AP configured, do not allow external WPS Registrars)
100 # If UUID is not configured, it will be generated based on local MAC address.
101 uuid=87654321-9abc-def0-1234-56789abc0000
102 wps_pin_requests=/var/run/hostapd.pin-req
103 device_name=Wireless AP
108 device_type=6-0050F204-1
110 config_methods=label display push_button keypad
112 # if external Registrars are allowed, UPnP support could be added:
114 #friendly_name=WPS Access Point
120 WPS requires either a device PIN code (usually, 8-digit number) or a
121 pushbutton event (for PBC) to allow a new WPS Enrollee to join the
122 network. hostapd uses the control interface as an input channel for
125 The PIN value used in the commands must be processed by an UI to
126 remove non-digit characters and potentially, to verify the checksum
127 digit. "hostapd_cli wps_check_pin <PIN>" can be used to do such
128 processing. It returns FAIL if the PIN is invalid, or FAIL-CHECKSUM if
129 the checksum digit is incorrect, or the processed PIN (non-digit
130 characters removed) if the PIN is valid.
132 When a client device (WPS Enrollee) connects to hostapd (WPS
133 Registrar) in order to start PIN mode negotiation for WPS, an
134 identifier (Enrollee UUID) is sent. hostapd will need to be configured
135 with a device password (PIN) for this Enrollee. This is an operation
136 that requires user interaction (assuming there are no pre-configured
137 PINs on the AP for a set of Enrollee).
139 The PIN request with information about the device is appended to the
140 wps_pin_requests file (/var/run/hostapd.pin-req in this example). In
141 addition, hostapd control interface event is sent as a notification of
142 a new device. The AP could use, e.g., a web UI for showing active
143 Enrollees to the user and request a PIN for an Enrollee.
145 The PIN request file has one line for every Enrollee that connected to
146 the AP, but for which there was no PIN. Following information is
147 provided for each Enrollee (separated with tabulators):
148 - timestamp (seconds from 1970-01-01)
158 Example line in the /var/run/hostapd.pin-req file:
159 1200188391 53b63a98-d29e-4457-a2ed-094d7e6a669c Intel(R) Centrino(R) Intel Corporation Intel(R) Centrino(R) - - 1-0050F204-1
161 Control interface data:
162 WPS-PIN-NEEDED [UUID-E|MAC Address|Device Name|Manufacturer|Model Name|Model Number|Serial Number|Device Category]
164 <2>WPS-PIN-NEEDED [53b63a98-d29e-4457-a2ed-094d7e6a669c|02:12:34:56:78:9a|Device|Manuf|Model|Model Number|Serial Number|1-0050F204-1]
166 When the user enters a PIN for a pending Enrollee, e.g., on the web
167 UI), hostapd needs to be notified of the new PIN over the control
168 interface. This can be done either by using the UNIX domain socket
169 -based control interface directly (src/common/wpa_ctrl.c provides
170 helper functions for using the interface) or by calling hostapd_cli.
172 Example command to add a PIN (12345670) for an Enrollee:
174 hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670
176 If the UUID-E is not available (e.g., Enrollee waits for the Registrar
177 to be selected before connecting), wildcard UUID may be used to allow
178 the PIN to be used once with any UUID:
180 hostapd_cli wps_pin any 12345670
182 To reduce likelihood of PIN being used with other devices or of
183 forgetting an active PIN available for potential attackers, expiration
184 time in seconds can be set for the new PIN (value 0 indicates no
187 hostapd_cli wps_pin any 12345670 300
189 If the MAC address of the enrollee is known, it should be configured
190 to allow the AP to advertise list of authorized enrollees:
192 hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c \
193 12345670 300 00:11:22:33:44:55
196 After this, the Enrollee can connect to the AP again and complete WPS
197 negotiation. At that point, a new, random WPA PSK is generated for the
198 client device and the client can then use that key to connect to the
199 AP to access the network.
202 If the AP includes a pushbutton, WPS PBC mode can be used. It is
203 enabled by pushing a button on both the AP and the client at about the
204 same time (2 minute window). hostapd needs to be notified about the AP
205 button pushed event over the control interface, e.g., by calling
210 At this point, the client has two minutes to complete WPS negotiation
211 which will generate a new WPA PSK in the same way as the PIN method
215 When an external Registrar is used, the AP can act as an Enrollee and
216 use its AP PIN. A static AP PIN (e.g., one one a label in the AP
217 device) can be configured in hostapd.conf (ap_pin parameter). A more
218 secure option is to use hostapd_cli wps_ap_pin command to enable the
219 AP PIN only based on user action (and even better security by using a
220 random AP PIN for each session, i.e., by using "wps_ap_pin random"
221 command with a timeout value). Following commands are available for
222 managing the dynamic AP PIN operations:
224 hostapd_cli wps_ap_pin disable
225 - disable AP PIN (i.e., do not allow external Registrars to use it to
226 learn the current AP settings or to reconfigure the AP)
228 hostapd_cli wps_ap_pin random [timeout]
229 - generate a random AP PIN and enable it
230 - if the optional timeout parameter is given, the AP PIN will be enabled
231 for the specified number of seconds
233 hostapd_cli wps_ap_pin get
234 - fetch the current AP PIN
236 hostapd_cli wps_ap_pin set <PIN> [timeout]
237 - set the AP PIN and enable it
238 - if the optional timeout parameter is given, the AP PIN will be enabled
239 for the specified number of seconds
241 hostapd_cli get_config
242 - display the current configuration
244 hostapd_cli wps_config <new SSID> <auth> <encr> <new key>
246 hostapd_cli wps_config testing WPA2PSK CCMP 12345678
247 hostapd_cli wps_config "no security" OPEN NONE ""
249 <auth> must be one of the following: OPEN WPAPSK WPA2PSK
250 <encr> must be one of the following: NONE WEP TKIP CCMP
253 Credential generation and configuration changes
254 -----------------------------------------------
256 By default, hostapd generates credentials for Enrollees and processing
257 AP configuration updates internally. However, it is possible to
258 control these operations from external programs, if desired.
260 The internal credential generation can be disabled with
261 skip_cred_build=1 option in the configuration. extra_cred option will
262 then need to be used to provide pre-configured Credential attribute(s)
263 for hostapd to use. The exact data from this binary file will be sent,
264 i.e., it will have to include valid WPS attributes. extra_cred can
265 also be used to add additional networks if the Registrar is used to
266 configure credentials for multiple networks.
268 Processing of received configuration updates can be disabled with
269 wps_cred_processing=1 option. When this is used, an external program
270 is responsible for creating hostapd configuration files and processing
271 configuration updates based on messages received from hostapd over
272 control interface. This will also include the initial configuration on
273 first successful registration if the AP is initially set in
276 Following control interface messages are sent out for external programs:
278 WPS-REG-SUCCESS <Enrollee MAC address <UUID-E>
280 <2>WPS-REG-SUCCESS 02:66:a0:ee:17:27 2b7093f1-d6fb-5108-adbb-bea66bb87333
282 This can be used to trigger change from unconfigured to configured
283 state (random configuration based on the first successful WPS
284 registration). In addition, this can be used to update AP UI about the
285 status of WPS registration progress.
288 WPS-NEW-AP-SETTINGS <hexdump of AP Setup attributes>
290 <2>WPS-NEW-AP-SETTINGS 10260001011045000c6a6b6d2d7770732d74657374100300020020100f00020008102700403065346230343536633236366665306433396164313535346131663462663731323433376163666462376633393965353466316631623032306164343438623510200006024231cede15101e000844
292 This can be used to update the externally stored AP configuration and
293 then update hostapd configuration (followed by restarting of hostapd).
299 WPS can be used with NFC-based configuration method. An NFC tag
300 containing a password token from the Enrollee can be used to
301 authenticate the connection instead of the PIN. In addition, an NFC tag
302 with a configuration token can be used to transfer AP settings without
303 going through the WPS protocol.
305 When the AP acts as an Enrollee, a local NFC tag with a password token
306 can be used by touching the NFC interface of an external Registrar. The
307 wps_nfc_token command is used to manage use of the NFC password token
308 from the AP. "wps_nfc_token enable" enables the use of the AP's NFC
309 password token (in place of AP PIN) and "wps_nfc_token disable" disables
310 the NFC password token.
312 The NFC password token that is either pre-configured in the
313 configuration file (wps_nfc_dev_pw_id, wps_nfc_dh_pubkey,
314 wps_nfc_dh_privkey, wps_nfc_dev_pw) or generated dynamically with
315 "wps_nfc_token <WPS|NDEF>" command. The nfc_pw_token tool from
316 wpa_supplicant can be used to generate NFC password tokens during
317 manufacturing (each AP needs to have its own random keys).
319 The "wps_nfc_config_token <WPS/NDEF>" command can be used to build an
320 NFC configuration token. The output value from this command is a hexdump
321 of the current AP configuration (WPS parameter requests this to include
322 only the WPS attributes; NDEF parameter requests additional NDEF
323 encapsulation to be included). This data needs to be written to an NFC
324 tag with an external program. Once written, the NFC configuration token
325 can be used to touch an NFC interface on a station to provision the
326 credentials needed to access the network.
328 When the NFC device on the AP reads an NFC tag with a MIME media type
329 "application/vnd.wfa.wsc", the NDEF message payload (with or without
330 NDEF encapsulation) can be delivered to hostapd using the
331 following hostapd_cli command:
333 wps_nfc_tag_read <hexdump of payload>
335 If the NFC tag contains a password token, the token is added to the
336 internal Registrar. This allows station Enrollee from which the password
337 token was received to run through WPS protocol to provision the
340 "nfc_get_handover_sel <NDEF> <WPS>" command can be used to build the
341 contents of a Handover Select Message for connection handover when this
342 does not depend on the contents of the Handover Request Message. The
343 first argument selects the format of the output data and the second
344 argument selects which type of connection handover is requested (WPS =
345 Wi-Fi handover as specified in WSC 2.0).
347 "nfc_report_handover <INIT/RESP> WPS <carrier from handover request>
348 <carrier from handover select>" is used to report completed NFC
349 connection handover. The first parameter indicates whether the local
350 device initiated or responded to the connection handover and the carrier
351 records are the selected carrier from the handover request and select
352 messages as a hexdump.