1wpa_supplicant and Wi-Fi Protected Setup (WPS) 2============================================== 3 4This document describes how the WPS implementation in wpa_supplicant 5can be configured and how an external component on the client (e.g., 6management GUI) is used to enable WPS enrollment and registrar 7registration. 8 9 10Introduction to WPS 11------------------- 12 13Wi-Fi Protected Setup (WPS) is a mechanism for easy configuration of a 14wireless network. It allows automated generation of random keys (WPA 15passphrase/PSK) and configuration of an access point and client 16devices. WPS includes number of methods for setting up connections 17with PIN method and push-button configuration (PBC) being the most 18commonly deployed options. 19 20While WPS can enable more home networks to use encryption in the 21wireless network, it should be noted that the use of the PIN and 22especially PBC mechanisms for authenticating the initial key setup is 23not very secure. As such, use of WPS may not be suitable for 24environments that require secure network access without chance for 25allowing outsiders to gain access during the setup phase. 26 27WPS uses following terms to describe the entities participating in the 28network setup: 29- access point: the WLAN access point 30- Registrar: a device that control a network and can authorize 31 addition of new devices); this may be either in the AP ("internal 32 Registrar") or in an external device, e.g., a laptop, ("external 33 Registrar") 34- Enrollee: a device that is being authorized to use the network 35 36It should also be noted that the AP and a client device may change 37roles (i.e., AP acts as an Enrollee and client device as a Registrar) 38when WPS is used to configure the access point. 39 40 41More information about WPS is available from Wi-Fi Alliance: 42http://www.wi-fi.org/wifi-protected-setup 43 44 45wpa_supplicant implementation 46----------------------------- 47 48wpa_supplicant includes an optional WPS component that can be used as 49an Enrollee to enroll new network credential or as a Registrar to 50configure an AP. The current version of wpa_supplicant does not 51support operation as an external WLAN Management Registrar for adding 52new client devices or configuring the AP over UPnP. 53 54 55wpa_supplicant configuration 56---------------------------- 57 58WPS is an optional component that needs to be enabled in 59wpa_supplicant build configuration (.config). Here is an example 60configuration that includes WPS support and Linux wireless extensions 61-based driver interface: 62 63CONFIG_DRIVER_WEXT=y 64CONFIG_EAP=y 65CONFIG_WPS=y 66 67 68WPS needs the Universally Unique IDentifier (UUID; see RFC 4122) for 69the device. This is configured in the runtime configuration for 70wpa_supplicant (if not set, UUID will be generated based on local MAC 71address): 72 73# example UUID for WPS 74uuid=12345678-9abc-def0-1234-56789abcdef0 75 76The network configuration blocks needed for WPS are added 77automatically based on control interface commands, so they do not need 78to be added explicitly in the configuration file. 79 80WPS registration will generate new network blocks for the acquired 81credentials. If these are to be stored for future use (after 82restarting wpa_supplicant), wpa_supplicant will need to be configured 83to allow configuration file updates: 84 85update_config=1 86 87 88 89External operations 90------------------- 91 92WPS requires either a device PIN code (usually, 8-digit number) or a 93pushbutton event (for PBC) to allow a new WPS Enrollee to join the 94network. wpa_supplicant uses the control interface as an input channel 95for these events. 96 97If the client device has a display, a random PIN has to be generated 98for each WPS registration session. wpa_supplicant can do this with a 99control interface request, e.g., by calling wpa_cli: 100 101wpa_cli wps_pin any 102 103This will return the generated 8-digit PIN which will then need to be 104entered at the Registrar to complete WPS registration. At that point, 105the client will be enrolled with credentials needed to connect to the 106AP to access the network. 107 108 109If the client device does not have a display that could show the 110random PIN, a hardcoded PIN that is printed on a label can be 111used. wpa_supplicant is notified this with a control interface 112request, e.g., by calling wpa_cli: 113 114wpa_cli wps_pin any 12345670 115 116This starts the WPS negotiation in the same way as above with the 117generated PIN. 118 119 120If the client design wants to support optional WPS PBC mode, this can 121be enabled by either a physical button in the client device or a 122virtual button in the user interface. The PBC operation requires that 123a button is also pressed at the AP/Registrar at about the same time (2 124minute window). wpa_supplicant is notified of the local button event 125over the control interface, e.g., by calling wpa_cli: 126 127wpa_cli wps_pbc 128 129At this point, the AP/Registrar has two minutes to complete WPS 130negotiation which will generate a new WPA PSK in the same way as the 131PIN method described above. 132 133 134If the client wants to operate in the Registrar role to configure an 135AP, wpa_supplicant is notified over the control interface, e.g., with 136wpa_cli: 137 138wpa_cli wps_reg <AP BSSID> <AP PIN> 139(example: wpa_cli wps_reg 02:34:56:78:9a:bc 12345670) 140 141This is currently only used to fetch the current AP settings instead 142of actually changing them. The main difference with the wps_pin 143command is that wps_reg uses the AP PIN (e.g., from a label on the AP) 144instead of a PIN generated at the client. 145 146 147Scanning 148-------- 149 150Scan results ('wpa_cli scan_results' or 'wpa_cli bss <idx>') include a 151flags field that is used to indicate whether the BSS support WPS. If 152the AP support WPS, but has not recently activated a Registrar, [WPS] 153flag will be included. If PIN method has been recently selected, 154[WPS-PIN] is shown instead. Similarly, [WPS-PBC] is shown if PBC mode 155is in progress. GUI programs can use these as triggers for suggesting 156a guided WPS configuration to the user. In addition, control interface 157monitor events WPS-AP-AVAILABLE{,-PBC,-PIN} can be used to find out if 158there are WPS enabled APs in scan results without having to go through 159all the details in the GUI. These notification could be used, e.g., to 160suggest possible WPS connection to the user. 161 162 163wpa_gui 164------- 165 166wpa_gui-qt4 directory contains a sample GUI that shows an example of 167how WPS support can be integrated into the GUI. Its main window has a 168WPS tab that guides user through WPS registration with automatic AP 169selection. In addition, it shows how WPS can be started manually by 170selecting an AP from scan results. 171 172 173Credential processing 174--------------------- 175 176By default, wpa_supplicant processes received credentials and updates 177its configuration internally. However, it is possible to 178control these operations from external programs, if desired. 179 180This internal processing can be disabled with wps_cred_processing=1 181option. When this is used, an external program is responsible for 182processing the credential attributes and updating wpa_supplicant 183configuration based on them. 184 185Following control interface messages are sent out for external programs: 186 187WPS-CRED-RECEIVED <hexdump of Credential attribute(s)> 188For example: 189<2>WPS-CRED-RECEIVED 100e006f10260001011045000c6a6b6d2d7770732d74657374100300020020100f000200081027004030653462303435366332363666653064333961643135353461316634626637313234333761636664623766333939653534663166316230323061643434386235102000060266a0ee1727 190