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 madwifi driver interface:
62
63CONFIG_DRIVER_MADWIFI=y
64CFLAGS += -I/usr/src/madwifi-0.9.3
65CONFIG_WPS=y
66CONFIG_WPS2=y
67CONFIG_WPS_UPNP=y
68
69Following parameter can be used to enable support for NFC config method:
70
71CONFIG_WPS_NFC=y
72
73
74Following section shows an example runtime configuration
75(hostapd.conf) that enables WPS:
76
77# Configure the driver and network interface
78driver=madwifi
79interface=ath0
80
81# WPA2-Personal configuration for the AP
82ssid=wps-test
83wpa=2
84wpa_key_mgmt=WPA-PSK
85wpa_pairwise=CCMP
86# Default WPA passphrase for legacy (non-WPS) clients
87wpa_passphrase=12345678
88# Enable random per-device PSK generation for WPS clients
89# Please note that the file has to exists for hostapd to start (i.e., create an
90# empty file as a starting point).
91wpa_psk_file=/etc/hostapd.psk
92
93# Enable control interface for PBC/PIN entry
94ctrl_interface=/var/run/hostapd
95
96# Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup)
97eap_server=1
98
99# WPS configuration (AP configured, do not allow external WPS Registrars)
100wps_state=2
101ap_setup_locked=1
102# If UUID is not configured, it will be generated based on local MAC address.
103uuid=87654321-9abc-def0-1234-56789abc0000
104wps_pin_requests=/var/run/hostapd.pin-req
105device_name=Wireless AP
106manufacturer=Company
107model_name=WAP
108model_number=123
109serial_number=12345
110device_type=6-0050F204-1
111os_version=01020300
112config_methods=label display push_button keypad
113
114# if external Registrars are allowed, UPnP support could be added:
115#upnp_iface=br0
116#friendly_name=WPS Access Point
117
118
119External operations
120-------------------
121
122WPS requires either a device PIN code (usually, 8-digit number) or a
123pushbutton event (for PBC) to allow a new WPS Enrollee to join the
124network. hostapd uses the control interface as an input channel for
125these events.
126
127The PIN value used in the commands must be processed by an UI to
128remove non-digit characters and potentially, to verify the checksum
129digit. "hostapd_cli wps_check_pin <PIN>" can be used to do such
130processing. It returns FAIL if the PIN is invalid, or FAIL-CHECKSUM if
131the checksum digit is incorrect, or the processed PIN (non-digit
132characters removed) if the PIN is valid.
133
134When a client device (WPS Enrollee) connects to hostapd (WPS
135Registrar) in order to start PIN mode negotiation for WPS, an
136identifier (Enrollee UUID) is sent. hostapd will need to be configured
137with a device password (PIN) for this Enrollee. This is an operation
138that requires user interaction (assuming there are no pre-configured
139PINs on the AP for a set of Enrollee).
140
141The PIN request with information about the device is appended to the
142wps_pin_requests file (/var/run/hostapd.pin-req in this example). In
143addition, hostapd control interface event is sent as a notification of
144a new device. The AP could use, e.g., a web UI for showing active
145Enrollees to the user and request a PIN for an Enrollee.
146
147The PIN request file has one line for every Enrollee that connected to
148the AP, but for which there was no PIN. Following information is
149provided for each Enrollee (separated with tabulators):
150- timestamp (seconds from 1970-01-01)
151- Enrollee UUID
152- MAC address
153- Device name
154- Manufacturer
155- Model Name
156- Model Number
157- Serial Number
158- Device category
159
160Example line in the /var/run/hostapd.pin-req file:
1611200188391	53b63a98-d29e-4457-a2ed-094d7e6a669c	Intel(R) Centrino(R)	Intel Corporation	Intel(R) Centrino(R)	-	-	1-0050F204-1
162
163Control interface data:
164WPS-PIN-NEEDED [UUID-E|MAC Address|Device Name|Manufacturer|Model Name|Model Number|Serial Number|Device Category]
165For example:
166<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]
167
168When the user enters a PIN for a pending Enrollee, e.g., on the web
169UI), hostapd needs to be notified of the new PIN over the control
170interface. This can be done either by using the UNIX domain socket
171-based control interface directly (src/common/wpa_ctrl.c provides
172helper functions for using the interface) or by calling hostapd_cli.
173
174Example command to add a PIN (12345670) for an Enrollee:
175
176hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670
177
178If the UUID-E is not available (e.g., Enrollee waits for the Registrar
179to be selected before connecting), wildcard UUID may be used to allow
180the PIN to be used once with any UUID:
181
182hostapd_cli wps_pin any 12345670
183
184To reduce likelihood of PIN being used with other devices or of
185forgetting an active PIN available for potential attackers, expiration
186time in seconds can be set for the new PIN (value 0 indicates no
187expiration):
188
189hostapd_cli wps_pin any 12345670 300
190
191If the MAC address of the enrollee is known, it should be configured
192to allow the AP to advertise list of authorized enrollees:
193
194hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c \
195	12345670 300 00:11:22:33:44:55
196
197
198After this, the Enrollee can connect to the AP again and complete WPS
199negotiation. At that point, a new, random WPA PSK is generated for the
200client device and the client can then use that key to connect to the
201AP to access the network.
202
203
204If the AP includes a pushbutton, WPS PBC mode can be used. It is
205enabled by pushing a button on both the AP and the client at about the
206same time (2 minute window). hostapd needs to be notified about the AP
207button pushed event over the control interface, e.g., by calling
208hostapd_cli:
209
210hostapd_cli wps_pbc
211
212At this point, the client has two minutes to complete WPS negotiation
213which will generate a new WPA PSK in the same way as the PIN method
214described above.
215
216
217When an external Registrar is used, the AP can act as an Enrollee and
218use its AP PIN. A static AP PIN (e.g., one one a label in the AP
219device) can be configured in hostapd.conf (ap_pin parameter). A more
220secure option is to use hostapd_cli wps_ap_pin command to enable the
221AP PIN only based on user action (and even better security by using a
222random AP PIN for each session, i.e., by using "wps_ap_pin random"
223command with a timeout value). Following commands are available for
224managing the dynamic AP PIN operations:
225
226hostapd_cli wps_ap_pin disable
227- disable AP PIN (i.e., do not allow external Registrars to use it to
228  learn the current AP settings or to reconfigure the AP)
229
230hostapd_cli wps_ap_pin random [timeout]
231- generate a random AP PIN and enable it
232- if the optional timeout parameter is given, the AP PIN will be enabled
233  for the specified number of seconds
234
235hostapd_cli wps_ap_pin get
236- fetch the current AP PIN
237
238hostapd_cli wps_ap_pin set <PIN> [timeout]
239- set the AP PIN and enable it
240- if the optional timeout parameter is given, the AP PIN will be enabled
241  for the specified number of seconds
242
243hostapd_cli get_config
244- display the current configuration
245
246hostapd_cli wps_config <new SSID> <auth> <encr> <new key>
247examples:
248  hostapd_cli wps_config testing WPA2PSK CCMP 12345678
249  hostapd_cli wps_config "no security" OPEN NONE ""
250
251<auth> must be one of the following: OPEN WPAPSK WPA2PSK
252<encr> must be one of the following: NONE WEP TKIP CCMP
253
254
255Credential generation and configuration changes
256-----------------------------------------------
257
258By default, hostapd generates credentials for Enrollees and processing
259AP configuration updates internally. However, it is possible to
260control these operations from external programs, if desired.
261
262The internal credential generation can be disabled with
263skip_cred_build=1 option in the configuration. extra_cred option will
264then need to be used to provide pre-configured Credential attribute(s)
265for hostapd to use. The exact data from this binary file will be sent,
266i.e., it will have to include valid WPS attributes. extra_cred can
267also be used to add additional networks if the Registrar is used to
268configure credentials for multiple networks.
269
270Processing of received configuration updates can be disabled with
271wps_cred_processing=1 option. When this is used, an external program
272is responsible for creating hostapd configuration files and processing
273configuration updates based on messages received from hostapd over
274control interface. This will also include the initial configuration on
275first successful registration if the AP is initially set in
276unconfigured state.
277
278Following control interface messages are sent out for external programs:
279
280WPS-REG-SUCCESS <Enrollee MAC address <UUID-E>
281For example:
282<2>WPS-REG-SUCCESS 02:66:a0:ee:17:27 2b7093f1-d6fb-5108-adbb-bea66bb87333
283
284This can be used to trigger change from unconfigured to configured
285state (random configuration based on the first successful WPS
286registration). In addition, this can be used to update AP UI about the
287status of WPS registration progress.
288
289
290WPS-NEW-AP-SETTINGS <hexdump of AP Setup attributes>
291For example:
292<2>WPS-NEW-AP-SETTINGS 10260001011045000c6a6b6d2d7770732d74657374100300020020100f00020008102700403065346230343536633236366665306433396164313535346131663462663731323433376163666462376633393965353466316631623032306164343438623510200006024231cede15101e000844
293
294This can be used to update the externally stored AP configuration and
295then update hostapd configuration (followed by restarting of hostapd).
296
297
298WPS with NFC
299------------
300
301WPS can be used with NFC-based configuration method. An NFC tag
302containing a password token from the Enrollee can be used to
303authenticate the connection instead of the PIN. In addition, an NFC tag
304with a configuration token can be used to transfer AP settings without
305going through the WPS protocol.
306
307When the AP acts as an Enrollee, a local NFC tag with a password token
308can be used by touching the NFC interface of an external Registrar. The
309wps_nfc_token command is used to manage use of the NFC password token
310from the AP. "wps_nfc_token enable" enables the use of the AP's NFC
311password token (in place of AP PIN) and "wps_nfc_token disable" disables
312the NFC password token.
313
314The NFC password token that is either pre-configured in the
315configuration file (wps_nfc_dev_pw_id, wps_nfc_dh_pubkey,
316wps_nfc_dh_privkey, wps_nfc_dev_pw) or generated dynamically with
317"wps_nfc_token <WPS|NDEF>" command. The nfc_pw_token tool from
318wpa_supplicant can be used to generate NFC password tokens during
319manufacturing (each AP needs to have its own random keys).
320
321The "wps_nfc_config_token <WPS/NDEF>" command can be used to build an
322NFC configuration token. The output value from this command is a hexdump
323of the current AP configuration (WPS parameter requests this to include
324only the WPS attributes; NDEF parameter requests additional NDEF
325encapsulation to be included). This data needs to be written to an NFC
326tag with an external program. Once written, the NFC configuration token
327can be used to touch an NFC interface on a station to provision the
328credentials needed to access the network.
329
330When the NFC device on the AP reads an NFC tag with a MIME media type
331"application/vnd.wfa.wsc", the NDEF message payload (with or without
332NDEF encapsulation) can be delivered to hostapd using the
333following hostapd_cli command:
334
335wps_nfc_tag_read <hexdump of payload>
336
337If the NFC tag contains a password token, the token is added to the
338internal Registrar. This allows station Enrollee from which the password
339token was received to run through WPS protocol to provision the
340credential.
341
342"nfc_get_handover_sel <NDEF> <WPS>" command can be used to build the
343contents of a Handover Select Message for connection handover when this
344does not depend on the contents of the Handover Request Message. The
345first argument selects the format of the output data and the second
346argument selects which type of connection handover is requested (WPS =
347Wi-Fi handover as specified in WSC 2.0).
348
349"nfc_report_handover <INIT/RESP> WPS <carrier from handover request>
350<carrier from handover select>" is used to report completed NFC
351connection handover. The first parameter indicates whether the local
352device initiated or responded to the connection handover and the carrier
353records are the selected carrier from the handover request and select
354messages as a hexdump.
355