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_WPS2=y 67 CONFIG_WPS_UPNP=y 68 69 Following parameter can be used to enable support for NFC config method: 70 71 CONFIG_WPS_NFC=y 72 73 74 Following section shows an example runtime configuration 75 (hostapd.conf) that enables WPS: 76 77 # Configure the driver and network interface 78 driver=madwifi 79 interface=ath0 80 81 # WPA2-Personal configuration for the AP 82 ssid=wps-test 83 wpa=2 84 wpa_key_mgmt=WPA-PSK 85 wpa_pairwise=CCMP 86 # Default WPA passphrase for legacy (non-WPS) clients 87 wpa_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). 91 wpa_psk_file=/etc/hostapd.psk 92 93 # Enable control interface for PBC/PIN entry 94 ctrl_interface=/var/run/hostapd 95 96 # Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup) 97 eap_server=1 98 99 # WPS configuration (AP configured, do not allow external WPS Registrars) 100 wps_state=2 101 ap_setup_locked=1 102 # If UUID is not configured, it will be generated based on local MAC address. 103 uuid=87654321-9abc-def0-1234-56789abc0000 104 wps_pin_requests=/var/run/hostapd.pin-req 105 device_name=Wireless AP 106 manufacturer=Company 107 model_name=WAP 108 model_number=123 109 serial_number=12345 110 device_type=6-0050F204-1 111 os_version=01020300 112 config_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 117 118 119 External operations 120 ------------------- 121 122 WPS requires either a device PIN code (usually, 8-digit number) or a 123 pushbutton event (for PBC) to allow a new WPS Enrollee to join the 124 network. hostapd uses the control interface as an input channel for 125 these events. 126 127 The PIN value used in the commands must be processed by an UI to 128 remove non-digit characters and potentially, to verify the checksum 129 digit. "hostapd_cli wps_check_pin <PIN>" can be used to do such 130 processing. It returns FAIL if the PIN is invalid, or FAIL-CHECKSUM if 131 the checksum digit is incorrect, or the processed PIN (non-digit 132 characters removed) if the PIN is valid. 133 134 When a client device (WPS Enrollee) connects to hostapd (WPS 135 Registrar) in order to start PIN mode negotiation for WPS, an 136 identifier (Enrollee UUID) is sent. hostapd will need to be configured 137 with a device password (PIN) for this Enrollee. This is an operation 138 that requires user interaction (assuming there are no pre-configured 139 PINs on the AP for a set of Enrollee). 140 141 The PIN request with information about the device is appended to the 142 wps_pin_requests file (/var/run/hostapd.pin-req in this example). In 143 addition, hostapd control interface event is sent as a notification of 144 a new device. The AP could use, e.g., a web UI for showing active 145 Enrollees to the user and request a PIN for an Enrollee. 146 147 The PIN request file has one line for every Enrollee that connected to 148 the AP, but for which there was no PIN. Following information is 149 provided 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 159 160 Example line in the /var/run/hostapd.pin-req file: 161 1200188391 53b63a98-d29e-4457-a2ed-094d7e6a669c Intel(R) Centrino(R) Intel Corporation Intel(R) Centrino(R) - - 1-0050F204-1 162 163 Control interface data: 164 WPS-PIN-NEEDED [UUID-E|MAC Address|Device Name|Manufacturer|Model Name|Model Number|Serial Number|Device Category] 165 For 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] 167 168 When the user enters a PIN for a pending Enrollee, e.g., on the web 169 UI), hostapd needs to be notified of the new PIN over the control 170 interface. This can be done either by using the UNIX domain socket 171 -based control interface directly (src/common/wpa_ctrl.c provides 172 helper functions for using the interface) or by calling hostapd_cli. 173 174 Example command to add a PIN (12345670) for an Enrollee: 175 176 hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670 177 178 If the UUID-E is not available (e.g., Enrollee waits for the Registrar 179 to be selected before connecting), wildcard UUID may be used to allow 180 the PIN to be used once with any UUID: 181 182 hostapd_cli wps_pin any 12345670 183 184 To reduce likelihood of PIN being used with other devices or of 185 forgetting an active PIN available for potential attackers, expiration 186 time in seconds can be set for the new PIN (value 0 indicates no 187 expiration): 188 189 hostapd_cli wps_pin any 12345670 300 190 191 If the MAC address of the enrollee is known, it should be configured 192 to allow the AP to advertise list of authorized enrollees: 193 194 hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c \ 195 12345670 300 00:11:22:33:44:55 196 197 198 After this, the Enrollee can connect to the AP again and complete WPS 199 negotiation. At that point, a new, random WPA PSK is generated for the 200 client device and the client can then use that key to connect to the 201 AP to access the network. 202 203 204 If the AP includes a pushbutton, WPS PBC mode can be used. It is 205 enabled by pushing a button on both the AP and the client at about the 206 same time (2 minute window). hostapd needs to be notified about the AP 207 button pushed event over the control interface, e.g., by calling 208 hostapd_cli: 209 210 hostapd_cli wps_pbc 211 212 At this point, the client has two minutes to complete WPS negotiation 213 which will generate a new WPA PSK in the same way as the PIN method 214 described above. 215 216 217 When an external Registrar is used, the AP can act as an Enrollee and 218 use its AP PIN. A static AP PIN (e.g., one one a label in the AP 219 device) can be configured in hostapd.conf (ap_pin parameter). A more 220 secure option is to use hostapd_cli wps_ap_pin command to enable the 221 AP PIN only based on user action (and even better security by using a 222 random AP PIN for each session, i.e., by using "wps_ap_pin random" 223 command with a timeout value). Following commands are available for 224 managing the dynamic AP PIN operations: 225 226 hostapd_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) 229 230 hostapd_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 234 235 hostapd_cli wps_ap_pin get 236 - fetch the current AP PIN 237 238 hostapd_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 242 243 hostapd_cli get_config 244 - display the current configuration 245 246 hostapd_cli wps_config <new SSID> <auth> <encr> <new key> 247 examples: 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 253 254 255 Credential generation and configuration changes 256 ----------------------------------------------- 257 258 By default, hostapd generates credentials for Enrollees and processing 259 AP configuration updates internally. However, it is possible to 260 control these operations from external programs, if desired. 261 262 The internal credential generation can be disabled with 263 skip_cred_build=1 option in the configuration. extra_cred option will 264 then need to be used to provide pre-configured Credential attribute(s) 265 for hostapd to use. The exact data from this binary file will be sent, 266 i.e., it will have to include valid WPS attributes. extra_cred can 267 also be used to add additional networks if the Registrar is used to 268 configure credentials for multiple networks. 269 270 Processing of received configuration updates can be disabled with 271 wps_cred_processing=1 option. When this is used, an external program 272 is responsible for creating hostapd configuration files and processing 273 configuration updates based on messages received from hostapd over 274 control interface. This will also include the initial configuration on 275 first successful registration if the AP is initially set in 276 unconfigured state. 277 278 Following control interface messages are sent out for external programs: 279 280 WPS-REG-SUCCESS <Enrollee MAC address <UUID-E> 281 For example: 282 <2>WPS-REG-SUCCESS 02:66:a0:ee:17:27 2b7093f1-d6fb-5108-adbb-bea66bb87333 283 284 This can be used to trigger change from unconfigured to configured 285 state (random configuration based on the first successful WPS 286 registration). In addition, this can be used to update AP UI about the 287 status of WPS registration progress. 288 289 290 WPS-NEW-AP-SETTINGS <hexdump of AP Setup attributes> 291 For example: 292 <2>WPS-NEW-AP-SETTINGS 10260001011045000c6a6b6d2d7770732d74657374100300020020100f00020008102700403065346230343536633236366665306433396164313535346131663462663731323433376163666462376633393965353466316631623032306164343438623510200006024231cede15101e000844 293 294 This can be used to update the externally stored AP configuration and 295 then update hostapd configuration (followed by restarting of hostapd). 296 297 298 WPS with NFC 299 ------------ 300 301 WPS can be used with NFC-based configuration method. An NFC tag 302 containing a password token from the Enrollee can be used to 303 authenticate the connection instead of the PIN. In addition, an NFC tag 304 with a configuration token can be used to transfer AP settings without 305 going through the WPS protocol. 306 307 When the AP acts as an Enrollee, a local NFC tag with a password token 308 can be used by touching the NFC interface of an external Registrar. The 309 wps_nfc_token command is used to manage use of the NFC password token 310 from the AP. "wps_nfc_token enable" enables the use of the AP's NFC 311 password token (in place of AP PIN) and "wps_nfc_token disable" disables 312 the NFC password token. 313 314 The NFC password token that is either pre-configured in the 315 configuration file (wps_nfc_dev_pw_id, wps_nfc_dh_pubkey, 316 wps_nfc_dh_privkey, wps_nfc_dev_pw) or generated dynamically with 317 "wps_nfc_token <WPS|NDEF>" command. The nfc_pw_token tool from 318 wpa_supplicant can be used to generate NFC password tokens during 319 manufacturing (each AP needs to have its own random keys). 320 321 The "wps_nfc_config_token <WPS/NDEF>" command can be used to build an 322 NFC configuration token. The output value from this command is a hexdump 323 of the current AP configuration (WPS parameter requests this to include 324 only the WPS attributes; NDEF parameter requests additional NDEF 325 encapsulation to be included). This data needs to be written to an NFC 326 tag with an external program. Once written, the NFC configuration token 327 can be used to touch an NFC interface on a station to provision the 328 credentials needed to access the network. 329 330 When 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 332 NDEF encapsulation) can be delivered to hostapd using the 333 following hostapd_cli command: 334 335 wps_nfc_tag_read <hexdump of payload> 336 337 If the NFC tag contains a password token, the token is added to the 338 internal Registrar. This allows station Enrollee from which the password 339 token was received to run through WPS protocol to provision the 340 credential. 341 342 "nfc_get_handover_sel <NDEF> <WPS>" command can be used to build the 343 contents of a Handover Select Message for connection handover when this 344 does not depend on the contents of the Handover Request Message. The 345 first argument selects the format of the output data and the second 346 argument selects which type of connection handover is requested (WPS = 347 Wi-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 351 connection handover. The first parameter indicates whether the local 352 device initiated or responded to the connection handover and the carrier 353 records are the selected carrier from the handover request and select 354 messages as a hexdump. 355
