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 70 Following section shows an example runtime configuration 71 (hostapd.conf) that enables WPS: 72 73 # Configure the driver and network interface 74 driver=madwifi 75 interface=ath0 76 77 # WPA2-Personal configuration for the AP 78 ssid=wps-test 79 wpa=2 80 wpa_key_mgmt=WPA-PSK 81 wpa_pairwise=CCMP 82 # Default WPA passphrase for legacy (non-WPS) clients 83 wpa_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). 87 wpa_psk_file=/etc/hostapd.psk 88 89 # Enable control interface for PBC/PIN entry 90 ctrl_interface=/var/run/hostapd 91 92 # Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup) 93 eap_server=1 94 95 # WPS configuration (AP configured, do not allow external WPS Registrars) 96 wps_state=2 97 ap_setup_locked=1 98 # If UUID is not configured, it will be generated based on local MAC address. 99 uuid=87654321-9abc-def0-1234-56789abc0000 100 wps_pin_requests=/var/run/hostapd.pin-req 101 device_name=Wireless AP 102 manufacturer=Company 103 model_name=WAP 104 model_number=123 105 serial_number=12345 106 device_type=6-0050F204-1 107 os_version=01020300 108 config_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 113 114 115 External operations 116 ------------------- 117 118 WPS requires either a device PIN code (usually, 8-digit number) or a 119 pushbutton event (for PBC) to allow a new WPS Enrollee to join the 120 network. hostapd uses the control interface as an input channel for 121 these events. 122 123 The PIN value used in the commands must be processed by an UI to 124 remove non-digit characters and potentially, to verify the checksum 125 digit. "hostapd_cli wps_check_pin <PIN>" can be used to do such 126 processing. It returns FAIL if the PIN is invalid, or FAIL-CHECKSUM if 127 the checksum digit is incorrect, or the processed PIN (non-digit 128 characters removed) if the PIN is valid. 129 130 When a client device (WPS Enrollee) connects to hostapd (WPS 131 Registrar) in order to start PIN mode negotiation for WPS, an 132 identifier (Enrollee UUID) is sent. hostapd will need to be configured 133 with a device password (PIN) for this Enrollee. This is an operation 134 that requires user interaction (assuming there are no pre-configured 135 PINs on the AP for a set of Enrollee). 136 137 The PIN request with information about the device is appended to the 138 wps_pin_requests file (/var/run/hostapd.pin-req in this example). In 139 addition, hostapd control interface event is sent as a notification of 140 a new device. The AP could use, e.g., a web UI for showing active 141 Enrollees to the user and request a PIN for an Enrollee. 142 143 The PIN request file has one line for every Enrollee that connected to 144 the AP, but for which there was no PIN. Following information is 145 provided for each Enrollee (separated with tabulators): 146 - timestamp (seconds from 1970-01-01) 147 - Enrollee UUID 148 - MAC address 149 - Device name 150 - Manufacturer 151 - Model Name 152 - Model Number 153 - Serial Number 154 - Device category 155 156 Example line in the /var/run/hostapd.pin-req file: 157 1200188391 53b63a98-d29e-4457-a2ed-094d7e6a669c Intel(R) Centrino(R) Intel Corporation Intel(R) Centrino(R) - - 1-0050F204-1 158 159 Control interface data: 160 WPS-PIN-NEEDED [UUID-E|MAC Address|Device Name|Manufacturer|Model Name|Model Number|Serial Number|Device Category] 161 For example: 162 <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] 163 164 When the user enters a PIN for a pending Enrollee, e.g., on the web 165 UI), hostapd needs to be notified of the new PIN over the control 166 interface. This can be done either by using the UNIX domain socket 167 -based control interface directly (src/common/wpa_ctrl.c provides 168 helper functions for using the interface) or by calling hostapd_cli. 169 170 Example command to add a PIN (12345670) for an Enrollee: 171 172 hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670 173 174 If the UUID-E is not available (e.g., Enrollee waits for the Registrar 175 to be selected before connecting), wildcard UUID may be used to allow 176 the PIN to be used once with any UUID: 177 178 hostapd_cli wps_pin any 12345670 179 180 To reduce likelihood of PIN being used with other devices or of 181 forgetting an active PIN available for potential attackers, expiration 182 time in seconds can be set for the new PIN (value 0 indicates no 183 expiration): 184 185 hostapd_cli wps_pin any 12345670 300 186 187 If the MAC address of the enrollee is known, it should be configured 188 to allow the AP to advertise list of authorized enrollees: 189 190 hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c \ 191 12345670 300 00:11:22:33:44:55 192 193 194 After this, the Enrollee can connect to the AP again and complete WPS 195 negotiation. At that point, a new, random WPA PSK is generated for the 196 client device and the client can then use that key to connect to the 197 AP to access the network. 198 199 200 If the AP includes a pushbutton, WPS PBC mode can be used. It is 201 enabled by pushing a button on both the AP and the client at about the 202 same time (2 minute window). hostapd needs to be notified about the AP 203 button pushed event over the control interface, e.g., by calling 204 hostapd_cli: 205 206 hostapd_cli wps_pbc 207 208 At this point, the client has two minutes to complete WPS negotiation 209 which will generate a new WPA PSK in the same way as the PIN method 210 described above. 211 212 213 When an external Registrar is used, the AP can act as an Enrollee and 214 use its AP PIN. A static AP PIN (e.g., one one a label in the AP 215 device) can be configured in hostapd.conf (ap_pin parameter). A more 216 secure option is to use hostapd_cli wps_ap_pin command to enable the 217 AP PIN only based on user action (and even better security by using a 218 random AP PIN for each session, i.e., by using "wps_ap_pin random" 219 command with a timeout value). Following commands are available for 220 managing the dynamic AP PIN operations: 221 222 hostapd_cli wps_ap_pin disable 223 - disable AP PIN (i.e., do not allow external Registrars to use it to 224 learn the current AP settings or to reconfigure the AP) 225 226 hostapd_cli wps_ap_pin random [timeout] 227 - generate a random AP PIN and enable it 228 - if the optional timeout parameter is given, the AP PIN will be enabled 229 for the specified number of seconds 230 231 hostapd_cli wps_ap_pin get 232 - fetch the current AP PIN 233 234 hostapd_cli wps_ap_pin set <PIN> [timeout] 235 - set the AP PIN and enable it 236 - if the optional timeout parameter is given, the AP PIN will be enabled 237 for the specified number of seconds 238 239 hostapd_cli get_config 240 - display the current configuration 241 242 hostapd_cli wps_config <new SSID> <auth> <encr> <new key> 243 examples: 244 hostapd_cli wps_config testing WPA2PSK CCMP 12345678 245 hostapd_cli wps_config "no security" OPEN NONE "" 246 247 <auth> must be one of the following: OPEN WPAPSK WPA2PSK 248 <encr> must be one of the following: NONE WEP TKIP CCMP 249 250 251 Credential generation and configuration changes 252 ----------------------------------------------- 253 254 By default, hostapd generates credentials for Enrollees and processing 255 AP configuration updates internally. However, it is possible to 256 control these operations from external programs, if desired. 257 258 The internal credential generation can be disabled with 259 skip_cred_build=1 option in the configuration. extra_cred option will 260 then need to be used to provide pre-configured Credential attribute(s) 261 for hostapd to use. The exact data from this binary file will be sent, 262 i.e., it will have to include valid WPS attributes. extra_cred can 263 also be used to add additional networks if the Registrar is used to 264 configure credentials for multiple networks. 265 266 Processing of received configuration updates can be disabled with 267 wps_cred_processing=1 option. When this is used, an external program 268 is responsible for creating hostapd configuration files and processing 269 configuration updates based on messages received from hostapd over 270 control interface. This will also include the initial configuration on 271 first successful registration if the AP is initially set in 272 unconfigured state. 273 274 Following control interface messages are sent out for external programs: 275 276 WPS-REG-SUCCESS <Enrollee MAC address <UUID-E> 277 For example: 278 <2>WPS-REG-SUCCESS 02:66:a0:ee:17:27 2b7093f1-d6fb-5108-adbb-bea66bb87333 279 280 This can be used to trigger change from unconfigured to configured 281 state (random configuration based on the first successful WPS 282 registration). In addition, this can be used to update AP UI about the 283 status of WPS registration progress. 284 285 286 WPS-NEW-AP-SETTINGS <hexdump of AP Setup attributes> 287 For example: 288 <2>WPS-NEW-AP-SETTINGS 10260001011045000c6a6b6d2d7770732d74657374100300020020100f00020008102700403065346230343536633236366665306433396164313535346131663462663731323433376163666462376633393965353466316631623032306164343438623510200006024231cede15101e000844 289 290 This can be used to update the externally stored AP configuration and 291 then update hostapd configuration (followed by restarting of hostapd). 292
