1hostapd and Wi-Fi Protected Setup (WPS)
2=======================================
3
4This document describes how the WPS implementation in hostapd can be
5configured and how an external component on an AP (e.g., web UI) is
6used to enable enrollment of client devices.
7
8
9Introduction to WPS
10-------------------
11
12Wi-Fi Protected Setup (WPS) is a mechanism for easy configuration of a
13wireless network. It allows automated generation of random keys (WPA
14passphrase/PSK) and configuration of an access point and client
15devices. WPS includes number of methods for setting up connections
16with PIN method and push-button configuration (PBC) being the most
17commonly deployed options.
18
19While WPS can enable more home networks to use encryption in the
20wireless network, it should be noted that the use of the PIN and
21especially PBC mechanisms for authenticating the initial key setup is
22not very secure. As such, use of WPS may not be suitable for
23environments that require secure network access without chance for
24allowing outsiders to gain access during the setup phase.
25
26WPS uses following terms to describe the entities participating in the
27network setup:
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
32  Registrar")
33- Enrollee: a device that is being authorized to use the network
34
35It should also be noted that the AP and a client device may change
36roles (i.e., AP acts as an Enrollee and client device as a Registrar)
37when WPS is used to configure the access point.
38
39
40More information about WPS is available from Wi-Fi Alliance:
41http://www.wi-fi.org/wifi-protected-setup
42
43
44hostapd implementation
45----------------------
46
47hostapd includes an optional WPS component that can be used as an
48internal WPS Registrar to manage addition of new WPS enabled clients
49to the network. In addition, WPS Enrollee functionality in hostapd can
50be used to allow external WPS Registrars to configure the access
51point, e.g., for initial network setup. In addition, hostapd can proxy a
52WPS registration between a wireless Enrollee and an external Registrar
53(e.g., Microsoft Vista or Atheros JumpStart) with UPnP.
54
55
56hostapd configuration
57---------------------
58
59WPS is an optional component that needs to be enabled in hostapd build
60configuration (.config). Here is an example configuration that
61includes WPS support and uses nl80211 driver interface:
62
63CONFIG_DRIVER_NL80211=y
64CONFIG_WPS=y
65CONFIG_WPS_UPNP=y
66
67Following parameter can be used to enable support for NFC config method:
68
69CONFIG_WPS_NFC=y
70
71
72Following section shows an example runtime configuration
73(hostapd.conf) that enables WPS:
74
75# Configure the driver and network interface
76driver=nl80211
77interface=wlan0
78
79# WPA2-Personal configuration for the AP
80ssid=wps-test
81wpa=2
82wpa_key_mgmt=WPA-PSK
83wpa_pairwise=CCMP
84# Default WPA passphrase for legacy (non-WPS) clients
85wpa_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).
89wpa_psk_file=/etc/hostapd.psk
90
91# Enable control interface for PBC/PIN entry
92ctrl_interface=/var/run/hostapd
93
94# Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup)
95eap_server=1
96
97# WPS configuration (AP configured, do not allow external WPS Registrars)
98wps_state=2
99ap_setup_locked=1
100# If UUID is not configured, it will be generated based on local MAC address.
101uuid=87654321-9abc-def0-1234-56789abc0000
102wps_pin_requests=/var/run/hostapd.pin-req
103device_name=Wireless AP
104manufacturer=Company
105model_name=WAP
106model_number=123
107serial_number=12345
108device_type=6-0050F204-1
109os_version=01020300
110config_methods=label display push_button keypad
111
112# if external Registrars are allowed, UPnP support could be added:
113#upnp_iface=br0
114#friendly_name=WPS Access Point
115
116
117External operations
118-------------------
119
120WPS requires either a device PIN code (usually, 8-digit number) or a
121pushbutton event (for PBC) to allow a new WPS Enrollee to join the
122network. hostapd uses the control interface as an input channel for
123these events.
124
125The PIN value used in the commands must be processed by an UI to
126remove non-digit characters and potentially, to verify the checksum
127digit. "hostapd_cli wps_check_pin <PIN>" can be used to do such
128processing. It returns FAIL if the PIN is invalid, or FAIL-CHECKSUM if
129the checksum digit is incorrect, or the processed PIN (non-digit
130characters removed) if the PIN is valid.
131
132When a client device (WPS Enrollee) connects to hostapd (WPS
133Registrar) in order to start PIN mode negotiation for WPS, an
134identifier (Enrollee UUID) is sent. hostapd will need to be configured
135with a device password (PIN) for this Enrollee. This is an operation
136that requires user interaction (assuming there are no pre-configured
137PINs on the AP for a set of Enrollee).
138
139The PIN request with information about the device is appended to the
140wps_pin_requests file (/var/run/hostapd.pin-req in this example). In
141addition, hostapd control interface event is sent as a notification of
142a new device. The AP could use, e.g., a web UI for showing active
143Enrollees to the user and request a PIN for an Enrollee.
144
145The PIN request file has one line for every Enrollee that connected to
146the AP, but for which there was no PIN. Following information is
147provided for each Enrollee (separated with tabulators):
148- timestamp (seconds from 1970-01-01)
149- Enrollee UUID
150- MAC address
151- Device name
152- Manufacturer
153- Model Name
154- Model Number
155- Serial Number
156- Device category
157
158Example line in the /var/run/hostapd.pin-req file:
1591200188391	53b63a98-d29e-4457-a2ed-094d7e6a669c	Intel(R) Centrino(R)	Intel Corporation	Intel(R) Centrino(R)	-	-	1-0050F204-1
160
161Control interface data:
162WPS-PIN-NEEDED [UUID-E|MAC Address|Device Name|Manufacturer|Model Name|Model Number|Serial Number|Device Category]
163For example:
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]
165
166When the user enters a PIN for a pending Enrollee, e.g., on the web
167UI), hostapd needs to be notified of the new PIN over the control
168interface. This can be done either by using the UNIX domain socket
169-based control interface directly (src/common/wpa_ctrl.c provides
170helper functions for using the interface) or by calling hostapd_cli.
171
172Example command to add a PIN (12345670) for an Enrollee:
173
174hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670
175
176If the UUID-E is not available (e.g., Enrollee waits for the Registrar
177to be selected before connecting), wildcard UUID may be used to allow
178the PIN to be used once with any UUID:
179
180hostapd_cli wps_pin any 12345670
181
182To reduce likelihood of PIN being used with other devices or of
183forgetting an active PIN available for potential attackers, expiration
184time in seconds can be set for the new PIN (value 0 indicates no
185expiration):
186
187hostapd_cli wps_pin any 12345670 300
188
189If the MAC address of the enrollee is known, it should be configured
190to allow the AP to advertise list of authorized enrollees:
191
192hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c \
193	12345670 300 00:11:22:33:44:55
194
195
196After this, the Enrollee can connect to the AP again and complete WPS
197negotiation. At that point, a new, random WPA PSK is generated for the
198client device and the client can then use that key to connect to the
199AP to access the network.
200
201
202If the AP includes a pushbutton, WPS PBC mode can be used. It is
203enabled by pushing a button on both the AP and the client at about the
204same time (2 minute window). hostapd needs to be notified about the AP
205button pushed event over the control interface, e.g., by calling
206hostapd_cli:
207
208hostapd_cli wps_pbc
209
210At this point, the client has two minutes to complete WPS negotiation
211which will generate a new WPA PSK in the same way as the PIN method
212described above.
213
214
215When an external Registrar is used, the AP can act as an Enrollee and
216use its AP PIN. A static AP PIN (e.g., one one a label in the AP
217device) can be configured in hostapd.conf (ap_pin parameter). A more
218secure option is to use hostapd_cli wps_ap_pin command to enable the
219AP PIN only based on user action (and even better security by using a
220random AP PIN for each session, i.e., by using "wps_ap_pin random"
221command with a timeout value). Following commands are available for
222managing the dynamic AP PIN operations:
223
224hostapd_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)
227
228hostapd_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
232
233hostapd_cli wps_ap_pin get
234- fetch the current AP PIN
235
236hostapd_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
240
241hostapd_cli get_config
242- display the current configuration
243
244hostapd_cli wps_config <new SSID> <auth> <encr> <new key>
245examples:
246  hostapd_cli wps_config testing WPA2PSK CCMP 12345678
247  hostapd_cli wps_config "no security" OPEN NONE ""
248
249<auth> must be one of the following: OPEN WPAPSK WPA2PSK
250<encr> must be one of the following: NONE WEP TKIP CCMP
251
252
253Credential generation and configuration changes
254-----------------------------------------------
255
256By default, hostapd generates credentials for Enrollees and processing
257AP configuration updates internally. However, it is possible to
258control these operations from external programs, if desired.
259
260The internal credential generation can be disabled with
261skip_cred_build=1 option in the configuration. extra_cred option will
262then need to be used to provide pre-configured Credential attribute(s)
263for hostapd to use. The exact data from this binary file will be sent,
264i.e., it will have to include valid WPS attributes. extra_cred can
265also be used to add additional networks if the Registrar is used to
266configure credentials for multiple networks.
267
268Processing of received configuration updates can be disabled with
269wps_cred_processing=1 option. When this is used, an external program
270is responsible for creating hostapd configuration files and processing
271configuration updates based on messages received from hostapd over
272control interface. This will also include the initial configuration on
273first successful registration if the AP is initially set in
274unconfigured state.
275
276Following control interface messages are sent out for external programs:
277
278WPS-REG-SUCCESS <Enrollee MAC address <UUID-E>
279For example:
280<2>WPS-REG-SUCCESS 02:66:a0:ee:17:27 2b7093f1-d6fb-5108-adbb-bea66bb87333
281
282This can be used to trigger change from unconfigured to configured
283state (random configuration based on the first successful WPS
284registration). In addition, this can be used to update AP UI about the
285status of WPS registration progress.
286
287
288WPS-NEW-AP-SETTINGS <hexdump of AP Setup attributes>
289For example:
290<2>WPS-NEW-AP-SETTINGS 10260001011045000c6a6b6d2d7770732d74657374100300020020100f00020008102700403065346230343536633236366665306433396164313535346131663462663731323433376163666462376633393965353466316631623032306164343438623510200006024231cede15101e000844
291
292This can be used to update the externally stored AP configuration and
293then update hostapd configuration (followed by restarting of hostapd).
294
295
296WPS with NFC
297------------
298
299WPS can be used with NFC-based configuration method. An NFC tag
300containing a password token from the Enrollee can be used to
301authenticate the connection instead of the PIN. In addition, an NFC tag
302with a configuration token can be used to transfer AP settings without
303going through the WPS protocol.
304
305When the AP acts as an Enrollee, a local NFC tag with a password token
306can be used by touching the NFC interface of an external Registrar. The
307wps_nfc_token command is used to manage use of the NFC password token
308from the AP. "wps_nfc_token enable" enables the use of the AP's NFC
309password token (in place of AP PIN) and "wps_nfc_token disable" disables
310the NFC password token.
311
312The NFC password token that is either pre-configured in the
313configuration file (wps_nfc_dev_pw_id, wps_nfc_dh_pubkey,
314wps_nfc_dh_privkey, wps_nfc_dev_pw) or generated dynamically with
315"wps_nfc_token <WPS|NDEF>" command. The nfc_pw_token tool from
316wpa_supplicant can be used to generate NFC password tokens during
317manufacturing (each AP needs to have its own random keys).
318
319The "wps_nfc_config_token <WPS/NDEF>" command can be used to build an
320NFC configuration token. The output value from this command is a hexdump
321of the current AP configuration (WPS parameter requests this to include
322only the WPS attributes; NDEF parameter requests additional NDEF
323encapsulation to be included). This data needs to be written to an NFC
324tag with an external program. Once written, the NFC configuration token
325can be used to touch an NFC interface on a station to provision the
326credentials needed to access the network.
327
328When 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
330NDEF encapsulation) can be delivered to hostapd using the
331following hostapd_cli command:
332
333wps_nfc_tag_read <hexdump of payload>
334
335If the NFC tag contains a password token, the token is added to the
336internal Registrar. This allows station Enrollee from which the password
337token was received to run through WPS protocol to provision the
338credential.
339
340"nfc_get_handover_sel <NDEF> <WPS>" command can be used to build the
341contents of a Handover Select Message for connection handover when this
342does not depend on the contents of the Handover Request Message. The
343first argument selects the format of the output data and the second
344argument selects which type of connection handover is requested (WPS =
345Wi-Fi handover as specified in WSC 2.0).
346
347"nfc_report_handover <INIT/RESP> WPS <carrier from handover request>
348<carrier from handover select>" is used to report completed NFC
349connection handover. The first parameter indicates whether the local
350device initiated or responded to the connection handover and the carrier
351records are the selected carrier from the handover request and select
352messages as a hexdump.
353