1 hostapd and Wi-Fi Protected Setup (WPS) 2 ======================================= 3 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. 7 8 9 Introduction to WPS 10 ------------------- 11 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. 18 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. 25 26 WPS uses following terms to describe the entities participating in the 27 network 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 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. 38 39 40 More information about WPS is available from Wi-Fi Alliance: 41 http://www.wi-fi.org/wifi-protected-setup 42 43 44 hostapd implementation 45 ---------------------- 46 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. 54 55 56 hostapd configuration 57 --------------------- 58 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 madwifi driver interface: 62 63 CONFIG_DRIVER_MADWIFI=y 64 CFLAGS += -I/usr/src/madwifi-0.9.3 65 CONFIG_WPS=y 66 CONFIG_WPS_UPNP=y 67 68 Following parameter can be used to enable support for NFC config method: 69 70 CONFIG_WPS_NFC=y 71 72 73 Following section shows an example runtime configuration 74 (hostapd.conf) that enables WPS: 75 76 # Configure the driver and network interface 77 driver=madwifi 78 interface=ath0 79 80 # WPA2-Personal configuration for the AP 81 ssid=wps-test 82 wpa=2 83 wpa_key_mgmt=WPA-PSK 84 wpa_pairwise=CCMP 85 # Default WPA passphrase for legacy (non-WPS) clients 86 wpa_passphrase=12345678 87 # Enable random per-device PSK generation for WPS clients 88 # Please note that the file has to exists for hostapd to start (i.e., create an 89 # empty file as a starting point). 90 wpa_psk_file=/etc/hostapd.psk 91 92 # Enable control interface for PBC/PIN entry 93 ctrl_interface=/var/run/hostapd 94 95 # Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup) 96 eap_server=1 97 98 # WPS configuration (AP configured, do not allow external WPS Registrars) 99 wps_state=2 100 ap_setup_locked=1 101 # If UUID is not configured, it will be generated based on local MAC address. 102 uuid=87654321-9abc-def0-1234-56789abc0000 103 wps_pin_requests=/var/run/hostapd.pin-req 104 device_name=Wireless AP 105 manufacturer=Company 106 model_name=WAP 107 model_number=123 108 serial_number=12345 109 device_type=6-0050F204-1 110 os_version=01020300 111 config_methods=label display push_button keypad 112 113 # if external Registrars are allowed, UPnP support could be added: 114 #upnp_iface=br0 115 #friendly_name=WPS Access Point 116 117 118 External operations 119 ------------------- 120 121 WPS requires either a device PIN code (usually, 8-digit number) or a 122 pushbutton event (for PBC) to allow a new WPS Enrollee to join the 123 network. hostapd uses the control interface as an input channel for 124 these events. 125 126 The PIN value used in the commands must be processed by an UI to 127 remove non-digit characters and potentially, to verify the checksum 128 digit. "hostapd_cli wps_check_pin <PIN>" can be used to do such 129 processing. It returns FAIL if the PIN is invalid, or FAIL-CHECKSUM if 130 the checksum digit is incorrect, or the processed PIN (non-digit 131 characters removed) if the PIN is valid. 132 133 When a client device (WPS Enrollee) connects to hostapd (WPS 134 Registrar) in order to start PIN mode negotiation for WPS, an 135 identifier (Enrollee UUID) is sent. hostapd will need to be configured 136 with a device password (PIN) for this Enrollee. This is an operation 137 that requires user interaction (assuming there are no pre-configured 138 PINs on the AP for a set of Enrollee). 139 140 The PIN request with information about the device is appended to the 141 wps_pin_requests file (/var/run/hostapd.pin-req in this example). In 142 addition, hostapd control interface event is sent as a notification of 143 a new device. The AP could use, e.g., a web UI for showing active 144 Enrollees to the user and request a PIN for an Enrollee. 145 146 The PIN request file has one line for every Enrollee that connected to 147 the AP, but for which there was no PIN. Following information is 148 provided for each Enrollee (separated with tabulators): 149 - timestamp (seconds from 1970-01-01) 150 - Enrollee UUID 151 - MAC address 152 - Device name 153 - Manufacturer 154 - Model Name 155 - Model Number 156 - Serial Number 157 - Device category 158 159 Example line in the /var/run/hostapd.pin-req file: 160 1200188391 53b63a98-d29e-4457-a2ed-094d7e6a669c Intel(R) Centrino(R) Intel Corporation Intel(R) Centrino(R) - - 1-0050F204-1 161 162 Control interface data: 163 WPS-PIN-NEEDED [UUID-E|MAC Address|Device Name|Manufacturer|Model Name|Model Number|Serial Number|Device Category] 164 For example: 165 <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] 166 167 When the user enters a PIN for a pending Enrollee, e.g., on the web 168 UI), hostapd needs to be notified of the new PIN over the control 169 interface. This can be done either by using the UNIX domain socket 170 -based control interface directly (src/common/wpa_ctrl.c provides 171 helper functions for using the interface) or by calling hostapd_cli. 172 173 Example command to add a PIN (12345670) for an Enrollee: 174 175 hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670 176 177 If the UUID-E is not available (e.g., Enrollee waits for the Registrar 178 to be selected before connecting), wildcard UUID may be used to allow 179 the PIN to be used once with any UUID: 180 181 hostapd_cli wps_pin any 12345670 182 183 To reduce likelihood of PIN being used with other devices or of 184 forgetting an active PIN available for potential attackers, expiration 185 time in seconds can be set for the new PIN (value 0 indicates no 186 expiration): 187 188 hostapd_cli wps_pin any 12345670 300 189 190 If the MAC address of the enrollee is known, it should be configured 191 to allow the AP to advertise list of authorized enrollees: 192 193 hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c \ 194 12345670 300 00:11:22:33:44:55 195 196 197 After this, the Enrollee can connect to the AP again and complete WPS 198 negotiation. At that point, a new, random WPA PSK is generated for the 199 client device and the client can then use that key to connect to the 200 AP to access the network. 201 202 203 If the AP includes a pushbutton, WPS PBC mode can be used. It is 204 enabled by pushing a button on both the AP and the client at about the 205 same time (2 minute window). hostapd needs to be notified about the AP 206 button pushed event over the control interface, e.g., by calling 207 hostapd_cli: 208 209 hostapd_cli wps_pbc 210 211 At this point, the client has two minutes to complete WPS negotiation 212 which will generate a new WPA PSK in the same way as the PIN method 213 described above. 214 215 216 When an external Registrar is used, the AP can act as an Enrollee and 217 use its AP PIN. A static AP PIN (e.g., one one a label in the AP 218 device) can be configured in hostapd.conf (ap_pin parameter). A more 219 secure option is to use hostapd_cli wps_ap_pin command to enable the 220 AP PIN only based on user action (and even better security by using a 221 random AP PIN for each session, i.e., by using "wps_ap_pin random" 222 command with a timeout value). Following commands are available for 223 managing the dynamic AP PIN operations: 224 225 hostapd_cli wps_ap_pin disable 226 - disable AP PIN (i.e., do not allow external Registrars to use it to 227 learn the current AP settings or to reconfigure the AP) 228 229 hostapd_cli wps_ap_pin random [timeout] 230 - generate a random AP PIN and enable it 231 - if the optional timeout parameter is given, the AP PIN will be enabled 232 for the specified number of seconds 233 234 hostapd_cli wps_ap_pin get 235 - fetch the current AP PIN 236 237 hostapd_cli wps_ap_pin set <PIN> [timeout] 238 - set the AP PIN and enable it 239 - if the optional timeout parameter is given, the AP PIN will be enabled 240 for the specified number of seconds 241 242 hostapd_cli get_config 243 - display the current configuration 244 245 hostapd_cli wps_config <new SSID> <auth> <encr> <new key> 246 examples: 247 hostapd_cli wps_config testing WPA2PSK CCMP 12345678 248 hostapd_cli wps_config "no security" OPEN NONE "" 249 250 <auth> must be one of the following: OPEN WPAPSK WPA2PSK 251 <encr> must be one of the following: NONE WEP TKIP CCMP 252 253 254 Credential generation and configuration changes 255 ----------------------------------------------- 256 257 By default, hostapd generates credentials for Enrollees and processing 258 AP configuration updates internally. However, it is possible to 259 control these operations from external programs, if desired. 260 261 The internal credential generation can be disabled with 262 skip_cred_build=1 option in the configuration. extra_cred option will 263 then need to be used to provide pre-configured Credential attribute(s) 264 for hostapd to use. The exact data from this binary file will be sent, 265 i.e., it will have to include valid WPS attributes. extra_cred can 266 also be used to add additional networks if the Registrar is used to 267 configure credentials for multiple networks. 268 269 Processing of received configuration updates can be disabled with 270 wps_cred_processing=1 option. When this is used, an external program 271 is responsible for creating hostapd configuration files and processing 272 configuration updates based on messages received from hostapd over 273 control interface. This will also include the initial configuration on 274 first successful registration if the AP is initially set in 275 unconfigured state. 276 277 Following control interface messages are sent out for external programs: 278 279 WPS-REG-SUCCESS <Enrollee MAC address <UUID-E> 280 For example: 281 <2>WPS-REG-SUCCESS 02:66:a0:ee:17:27 2b7093f1-d6fb-5108-adbb-bea66bb87333 282 283 This can be used to trigger change from unconfigured to configured 284 state (random configuration based on the first successful WPS 285 registration). In addition, this can be used to update AP UI about the 286 status of WPS registration progress. 287 288 289 WPS-NEW-AP-SETTINGS <hexdump of AP Setup attributes> 290 For example: 291 <2>WPS-NEW-AP-SETTINGS 10260001011045000c6a6b6d2d7770732d74657374100300020020100f00020008102700403065346230343536633236366665306433396164313535346131663462663731323433376163666462376633393965353466316631623032306164343438623510200006024231cede15101e000844 292 293 This can be used to update the externally stored AP configuration and 294 then update hostapd configuration (followed by restarting of hostapd). 295 296 297 WPS with NFC 298 ------------ 299 300 WPS can be used with NFC-based configuration method. An NFC tag 301 containing a password token from the Enrollee can be used to 302 authenticate the connection instead of the PIN. In addition, an NFC tag 303 with a configuration token can be used to transfer AP settings without 304 going through the WPS protocol. 305 306 When the AP acts as an Enrollee, a local NFC tag with a password token 307 can be used by touching the NFC interface of an external Registrar. The 308 wps_nfc_token command is used to manage use of the NFC password token 309 from the AP. "wps_nfc_token enable" enables the use of the AP's NFC 310 password token (in place of AP PIN) and "wps_nfc_token disable" disables 311 the NFC password token. 312 313 The NFC password token that is either pre-configured in the 314 configuration file (wps_nfc_dev_pw_id, wps_nfc_dh_pubkey, 315 wps_nfc_dh_privkey, wps_nfc_dev_pw) or generated dynamically with 316 "wps_nfc_token <WPS|NDEF>" command. The nfc_pw_token tool from 317 wpa_supplicant can be used to generate NFC password tokens during 318 manufacturing (each AP needs to have its own random keys). 319 320 The "wps_nfc_config_token <WPS/NDEF>" command can be used to build an 321 NFC configuration token. The output value from this command is a hexdump 322 of the current AP configuration (WPS parameter requests this to include 323 only the WPS attributes; NDEF parameter requests additional NDEF 324 encapsulation to be included). This data needs to be written to an NFC 325 tag with an external program. Once written, the NFC configuration token 326 can be used to touch an NFC interface on a station to provision the 327 credentials needed to access the network. 328 329 When the NFC device on the AP reads an NFC tag with a MIME media type 330 "application/vnd.wfa.wsc", the NDEF message payload (with or without 331 NDEF encapsulation) can be delivered to hostapd using the 332 following hostapd_cli command: 333 334 wps_nfc_tag_read <hexdump of payload> 335 336 If the NFC tag contains a password token, the token is added to the 337 internal Registrar. This allows station Enrollee from which the password 338 token was received to run through WPS protocol to provision the 339 credential. 340 341 "nfc_get_handover_sel <NDEF> <WPS>" command can be used to build the 342 contents of a Handover Select Message for connection handover when this 343 does not depend on the contents of the Handover Request Message. The 344 first argument selects the format of the output data and the second 345 argument selects which type of connection handover is requested (WPS = 346 Wi-Fi handover as specified in WSC 2.0). 347 348 "nfc_report_handover <INIT/RESP> WPS <carrier from handover request> 349 <carrier from handover select>" is used to report completed NFC 350 connection handover. The first parameter indicates whether the local 351 device initiated or responded to the connection handover and the carrier 352 records are the selected carrier from the handover request and select 353 messages as a hexdump. 354
