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_WPS_UPNP=y 67 68 69Following section shows an example runtime configuration 70(hostapd.conf) that enables WPS: 71 72# Configure the driver and network interface 73driver=madwifi 74interface=ath0 75 76# WPA2-Personal configuration for the AP 77ssid=wps-test 78wpa=2 79wpa_key_mgmt=WPA-PSK 80wpa_pairwise=CCMP 81# Default WPA passphrase for legacy (non-WPS) clients 82wpa_passphrase=12345678 83# Enable random per-device PSK generation for WPS clients 84# Please note that the file has to exists for hostapd to start (i.e., create an 85# empty file as a starting point). 86wpa_psk_file=/etc/hostapd.psk 87 88# Enable control interface for PBC/PIN entry 89ctrl_interface=/var/run/hostapd 90 91# Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup) 92eap_server=1 93 94# WPS configuration (AP configured, do not allow external WPS Registrars) 95wps_state=2 96ap_setup_locked=1 97# If UUID is not configured, it will be generated based on local MAC address. 98uuid=87654321-9abc-def0-1234-56789abc0000 99wps_pin_requests=/var/run/hostapd.pin-req 100device_name=Wireless AP 101manufacturer=Company 102model_name=WAP 103model_number=123 104serial_number=12345 105device_type=6-0050F204-1 106os_version=01020300 107config_methods=label display push_button keypad 108 109# if external Registrars are allowed, UPnP support could be added: 110#upnp_iface=br0 111#friendly_name=WPS Access Point 112 113 114External operations 115------------------- 116 117WPS requires either a device PIN code (usually, 8-digit number) or a 118pushbutton event (for PBC) to allow a new WPS Enrollee to join the 119network. hostapd uses the control interface as an input channel for 120these events. 121 122When a client device (WPS Enrollee) connects to hostapd (WPS 123Registrar) in order to start PIN mode negotiation for WPS, an 124identifier (Enrollee UUID) is sent. hostapd will need to be configured 125with a device password (PIN) for this Enrollee. This is an operation 126that requires user interaction (assuming there are no pre-configured 127PINs on the AP for a set of Enrollee). 128 129The PIN request with information about the device is appended to the 130wps_pin_requests file (/var/run/hostapd.pin-req in this example). In 131addition, hostapd control interface event is sent as a notification of 132a new device. The AP could use, e.g., a web UI for showing active 133Enrollees to the user and request a PIN for an Enrollee. 134 135The PIN request file has one line for every Enrollee that connected to 136the AP, but for which there was no PIN. Following information is 137provided for each Enrollee (separated with tabulators): 138- timestamp (seconds from 1970-01-01) 139- Enrollee UUID 140- MAC address 141- Device name 142- Manufacturer 143- Model Name 144- Model Number 145- Serial Number 146- Device category 147 148Example line in the /var/run/hostapd.pin-req file: 1491200188391 53b63a98-d29e-4457-a2ed-094d7e6a669c Intel(R) Centrino(R) Intel Corporation Intel(R) Centrino(R) - - 1-0050F204-1 150 151Control interface data: 152WPS-PIN-NEEDED [UUID-E|MAC Address|Device Name|Manufacturer|Model Name|Model Number|Serial Number|Device Category] 153For example: 154<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] 155 156When the user enters a PIN for a pending Enrollee, e.g., on the web 157UI), hostapd needs to be notified of the new PIN over the control 158interface. This can be done either by using the UNIX domain socket 159-based control interface directly (src/common/wpa_ctrl.c provides 160helper functions for using the interface) or by calling hostapd_cli. 161 162Example command to add a PIN (12345670) for an Enrollee: 163 164hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670 165 166If the UUID-E is not available (e.g., Enrollee waits for the Registrar 167to be selected before connecting), wildcard UUID may be used to allow 168the PIN to be used once with any UUID: 169 170hostapd_cli wps_pin any 12345670 171 172To reduce likelihood of PIN being used with other devices or of 173forgetting an active PIN available for potential attackers, expiration 174time can be set for the new PIN: 175 176hostapd_cli wps_pin any 12345670 300 177 178 179After this, the Enrollee can connect to the AP again and complete WPS 180negotiation. At that point, a new, random WPA PSK is generated for the 181client device and the client can then use that key to connect to the 182AP to access the network. 183 184 185If the AP includes a pushbutton, WPS PBC mode can be used. It is 186enabled by pushing a button on both the AP and the client at about the 187same time (2 minute window). hostapd needs to be notified about the AP 188button pushed event over the control interface, e.g., by calling 189hostapd_cli: 190 191hostapd_cli wps_pbc 192 193At this point, the client has two minutes to complete WPS negotiation 194which will generate a new WPA PSK in the same way as the PIN method 195described above. 196 197 198When an external Registrar is used, the AP can act as an Enrollee and 199use its AP PIN. A static AP PIN (e.g., one one a label in the AP 200device) can be configured in hostapd.conf (ap_pin parameter). A more 201secure option is to use hostapd_cli wps_ap_pin command to enable the 202AP PIN only based on user action (and even better security by using a 203random AP PIN for each session, i.e., by using "wps_ap_pin random" 204command with a timeout value). Following commands are available for 205managing the dynamic AP PIN operations: 206 207hostapd_cli wps_ap_pin disable 208- disable AP PIN (i.e., do not allow external Registrars to use it to 209 learn the current AP settings or to reconfigure the AP) 210 211hostapd_cli wps_ap_pin random [timeout] 212- generate a random AP PIN and enable it 213- if the optional timeout parameter is given, the AP PIN will be enabled 214 for the specified number of seconds 215 216hostapd_cli wps_ap_pin get 217- fetch the current AP PIN 218 219hostapd_cli wps_ap_pin set <PIN> [timeout] 220- set the AP PIN and enable it 221- if the optional timeout parameter is given, the AP PIN will be enabled 222 for the specified number of seconds 223 224 225Credential generation and configuration changes 226----------------------------------------------- 227 228By default, hostapd generates credentials for Enrollees and processing 229AP configuration updates internally. However, it is possible to 230control these operations from external programs, if desired. 231 232The internal credential generation can be disabled with 233skip_cred_build=1 option in the configuration. extra_cred option will 234then need to be used to provide pre-configured Credential attribute(s) 235for hostapd to use. The exact data from this binary file will be sent, 236i.e., it will have to include valid WPS attributes. extra_cred can 237also be used to add additional networks if the Registrar is used to 238configure credentials for multiple networks. 239 240Processing of received configuration updates can be disabled with 241wps_cred_processing=1 option. When this is used, an external program 242is responsible for creating hostapd configuration files and processing 243configuration updates based on messages received from hostapd over 244control interface. This will also include the initial configuration on 245first successful registration if the AP is initially set in 246unconfigured state. 247 248Following control interface messages are sent out for external programs: 249 250WPS-REG-SUCCESS <Enrollee MAC address <UUID-E> 251For example: 252<2>WPS-REG-SUCCESS 02:66:a0:ee:17:27 2b7093f1-d6fb-5108-adbb-bea66bb87333 253 254This can be used to tricker change from unconfigured to configured 255state (random configuration based on the first successful WPS 256registration). In addition, this can be used to update AP UI about the 257status of WPS registration progress. 258 259 260WPS-NEW-AP-SETTINGS <hexdump of AP Setup attributes> 261For example: 262<2>WPS-NEW-AP-SETTINGS 10260001011045000c6a6b6d2d7770732d74657374100300020020100f00020008102700403065346230343536633236366665306433396164313535346131663462663731323433376163666462376633393965353466316631623032306164343438623510200006024231cede15101e000844 263 264This can be used to update the externally stored AP configuration and 265then update hostapd configuration (followed by restarting of hostapd). 266