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_EAP=y 66CONFIG_WPS=y 67CONFIG_WPS_UPNP=y 68 69 70Following section shows an example runtime configuration 71(hostapd.conf) that enables WPS: 72 73# Configure the driver and network interface 74driver=madwifi 75interface=ath0 76 77# WPA2-Personal configuration for the AP 78ssid=wps-test 79wpa=2 80wpa_key_mgmt=WPA-PSK 81wpa_pairwise=CCMP 82# Default WPA passphrase for legacy (non-WPS) clients 83wpa_passphrase=12345678 84# Enable random per-device PSK generation for WPS clients 85# Please note that the file has to exists for hostapd to start (i.e., create an 86# empty file as a starting point). 87wpa_psk_file=/etc/hostapd.psk 88 89# Enable control interface for PBC/PIN entry 90ctrl_interface=/var/run/hostapd 91 92# Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup) 93eap_server=1 94 95# WPS configuration (AP configured, do not allow external WPS Registrars) 96wps_state=2 97ap_setup_locked=1 98# If UUID is not configured, it will be generated based on local MAC address. 99uuid=87654321-9abc-def0-1234-56789abc0000 100wps_pin_requests=/var/run/hostapd.pin-req 101device_name=Wireless AP 102manufacturer=Company 103model_name=WAP 104model_number=123 105serial_number=12345 106device_type=6-0050F204-1 107os_version=01020300 108config_methods=label display push_button keypad 109 110# if external Registrars are allowed, UPnP support could be added: 111#upnp_iface=br0 112#friendly_name=WPS Access Point 113 114 115External operations 116------------------- 117 118WPS requires either a device PIN code (usually, 8-digit number) or a 119pushbutton event (for PBC) to allow a new WPS Enrollee to join the 120network. hostapd uses the control interface as an input channel for 121these events. 122 123When a client device (WPS Enrollee) connects to hostapd (WPS 124Registrar) in order to start PIN mode negotiation for WPS, an 125identifier (Enrollee UUID) is sent. hostapd will need to be configured 126with a device password (PIN) for this Enrollee. This is an operation 127that requires user interaction (assuming there are no pre-configured 128PINs on the AP for a set of Enrollee). 129 130The PIN request with information about the device is appended to the 131wps_pin_requests file (/var/run/hostapd.pin-req in this example). In 132addition, hostapd control interface event is sent as a notification of 133a new device. The AP could use, e.g., a web UI for showing active 134Enrollees to the user and request a PIN for an Enrollee. 135 136The PIN request file has one line for every Enrollee that connected to 137the AP, but for which there was no PIN. Following information is 138provided for each Enrollee (separated with tabulators): 139- timestamp (seconds from 1970-01-01) 140- Enrollee UUID 141- MAC address 142- Device name 143- Manufacturer 144- Model Name 145- Model Number 146- Serial Number 147- Device category 148 149Example line in the /var/run/hostapd.pin-req file: 1501200188391 53b63a98-d29e-4457-a2ed-094d7e6a669c Intel(R) Centrino(R) Intel Corporation Intel(R) Centrino(R) - - 1-0050F204-1 151 152Control interface data: 153WPS-PIN-NEEDED [UUID-E|MAC Address|Device Name|Manufacturer|Model Name|Model Number|Serial Number|Device Category] 154For example: 155<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] 156 157When the user enters a PIN for a pending Enrollee, e.g., on the web 158UI), hostapd needs to be notified of the new PIN over the control 159interface. This can be done either by using the UNIX domain socket 160-based control interface directly (src/common/wpa_ctrl.c provides 161helper functions for using the interface) or by calling hostapd_cli. 162 163Example command to add a PIN (12345670) for an Enrollee: 164 165hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670 166 167If the UUID-E is not available (e.g., Enrollee waits for the Registrar 168to be selected before connecting), wildcard UUID may be used to allow 169the PIN to be used once with any UUID: 170 171hostapd_cli wps_pin any 12345670 172 173To reduce likelihood of PIN being used with other devices or of 174forgetting an active PIN available for potential attackers, expiration 175time can be set for the new PIN: 176 177hostapd_cli wps_pin any 12345670 300 178 179 180After this, the Enrollee can connect to the AP again and complete WPS 181negotiation. At that point, a new, random WPA PSK is generated for the 182client device and the client can then use that key to connect to the 183AP to access the network. 184 185 186If the AP includes a pushbutton, WPS PBC mode can be used. It is 187enabled by pushing a button on both the AP and the client at about the 188same time (2 minute window). hostapd needs to be notified about the AP 189button pushed event over the control interface, e.g., by calling 190hostapd_cli: 191 192hostapd_cli wps_pbc 193 194At this point, the client has two minutes to complete WPS negotiation 195which will generate a new WPA PSK in the same way as the PIN method 196described above. 197 198 199Credential generation and configuration changes 200----------------------------------------------- 201 202By default, hostapd generates credentials for Enrollees and processing 203AP configuration updates internally. However, it is possible to 204control these operations from external programs, if desired. 205 206The internal credential generation can be disabled with 207skip_cred_build=1 option in the configuration. extra_cred option will 208then need to be used to provide pre-configured Credential attribute(s) 209for hostapd to use. The exact data from this binary file will be sent, 210i.e., it will have to include valid WPS attributes. extra_cred can 211also be used to add additional networks if the Registrar is used to 212configure credentials for multiple networks. 213 214Processing of received configuration updates can be disabled with 215wps_cred_processing=1 option. When this is used, an external program 216is responsible for creating hostapd configuration files and processing 217configuration updates based on messages received from hostapd over 218control interface. This will also include the initial configuration on 219first successful registration if the AP is initially set in 220unconfigured state. 221 222Following control interface messages are sent out for external programs: 223 224WPS-REG-SUCCESS <Enrollee MAC address <UUID-E> 225For example: 226<2>WPS-REG-SUCCESS 02:66:a0:ee:17:27 2b7093f1-d6fb-5108-adbb-bea66bb87333 227 228This can be used to tricker change from unconfigured to configured 229state (random configuration based on the first successful WPS 230registration). In addition, this can be used to update AP UI about the 231status of WPS registration progress. 232 233 234WPS-NEW-AP-SETTINGS <hexdump of AP Setup attributes> 235For example: 236<2>WPS-NEW-AP-SETTINGS 10260001011045000c6a6b6d2d7770732d74657374100300020020100f00020008102700403065346230343536633236366665306433396164313535346131663462663731323433376163666462376633393965353466316631623032306164343438623510200006024231cede15101e000844 237 238This can be used to update the externally stored AP configuration and 239then update hostapd configuration (followed by restarting of hostapd). 240