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Since the Registrar may not yet know the UUID-E when a new PIN is entered, use of a wildcard PIN that works with any UUID-E can be useful. Such a PIN will be bound to the first Enrollee trying to use it and it will be invalidated after the first use.
180 lines
6.4 KiB
Plaintext
180 lines
6.4 KiB
Plaintext
hostapd and Wi-Fi Protected Setup (WPS)
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=======================================
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This document describes how the WPS implementation in hostapd can be
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configured and how an external component on an AP (e.g., web UI) is
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used to enable enrollment of client devices.
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Introduction to WPS
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-------------------
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Wi-Fi Protected Setup (WPS) is a mechanism for easy configuration of a
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wireless network. It allows automated generation of random keys (WPA
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passphrase/PSK) and configuration of an access point and client
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devices. WPS includes number of methods for setting up connections
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with PIN method and push-button configuration (PBC) being the most
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commonly deployed options.
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While WPS can enable more home networks to use encryption in the
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wireless network, it should be noted that the use of the PIN and
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especially PBC mechanisms for authenticating the initial key setup is
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not very secure. As such, use of WPS may not be suitable for
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environments that require secure network access without chance for
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allowing outsiders to gain access during the setup phase.
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WPS uses following terms to describe the entities participating in the
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network setup:
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- access point: the WLAN access point
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- Registrar: a device that control a network and can authorize
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addition of new devices); this may be either in the AP ("internal
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Registrar") or in an external device, e.g., a laptop, ("external
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Registrar")
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- Enrollee: a device that is being authorized to use the network
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It should also be noted that the AP and a client device may change
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roles (i.e., AP acts as an Enrollee and client device as a Registrar)
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when WPS is used to configure the access point.
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More information about WPS is available from Wi-Fi Alliance:
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http://www.wi-fi.org/wifi-protected-setup
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hostapd implementation
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----------------------
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hostapd includes an optional WPS component that can be used as an
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internal WPS Registrar to manage addition of new WPS enabled clients
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to the network. In addition, WPS Enrollee functionality in hostapd can
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be used to allow external WPS Registrars to configure the access
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point, e.g., for initial network setup. The current version of hostapd
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does not support use of external WPS Registrars for adding new client
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devices.
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hostapd configuration
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---------------------
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WPS is an optional component that needs to be enabled in hostapd build
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configuration (.config). Here is an example configuration that
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includes WPS support and uses madwifi driver interface:
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CONFIG_DRIVER_MADWIFI=y
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CFLAGS += -I/usr/src/madwifi-0.9.3
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CONFIG_EAP=y
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CONFIG_WPS=y
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Following section shows an example runtime configuration
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(hostapd.conf) that enables WPS:
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# Configure the driver and network interface
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driver=madwifi
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interface=ath0
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# WPA2-Personal configuration for the AP
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ssid=wps-test
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wpa=2
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wpa_key_mgmt=WPA-PSK
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wpa_pairwise=CCMP
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# Default WPA passphrase for legacy (non-WPS) clients
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wpa_passphrase=12345678
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# Enable random per-device PSK generation for WPS clients
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# Please note that the file has to exists for hostapd to start (i.e., create an
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# empty file as a starting point).
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wpa_psk_file=/etc/hostapd.psk
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# Enable control interface for PBC/PIN entry
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ctrl_interface=/var/run/hostapd
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# Enable internal EAP server for EAP-WSC (part of Wi-Fi Protected Setup)
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eap_server=1
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# WPS configuration (AP configured, do not allow external WPS Registrars)
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wps_state=2
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ap_setup_locked=1
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uuid=87654321-9abc-def0-1234-56789abc0000
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wps_pin_requests=/var/run/hostapd.pin-req
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device_name=Wireless AP
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manufacturer=Company
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model_name=WAP
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model_number=123
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serial_number=12345
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device_type=6-0050F204-1
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os_version=01020300
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config_methods=label display push_button keypad
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External operations
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-------------------
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WPS requires either a device PIN code (usually, 8-digit number) or a
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pushbutton event (for PBC) to allow a new WPS Enrollee to join the
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network. hostapd uses the control interface as an input channel for
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these events.
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When a client device (WPS Enrollee) connects to hostapd (WPS
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Registrar) in order to start PIN mode negotiation for WPS, an
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identifier (Enrollee UUID) is sent. hostapd will need to be configured
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with a device password (PIN) for this Enrollee. This is an operation
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that requires user interaction (assuming there are no pre-configured
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PINs on the AP for a set of Enrollee).
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The PIN request with information about the device is appended to the
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wps_pin_requests file (/var/run/hostapd.pin-req in this example). In
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addition, hostapd control interface event is sent as a notification of
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a new device. The AP could use, e.g., a web UI for showing active
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Enrollees to the user and request a PIN for an Enrollee.
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The PIN request file has one line for every Enrollee that connected to
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the AP, but for which there was no PIN. Following information is
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provided for each Enrollee (separated with tabulators):
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- timestamp (seconds from 1970-01-01)
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- Enrollee UUID
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- MAC address
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- Device name
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- Manufacturer
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- Model Name
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- Model Number
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- Serial Number
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- Device category
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Example line in the /var/run/hostapd.pin-req file:
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1200188391 53b63a98-d29e-4457-a2ed-094d7e6a669c Intel(R) Centrino(R) Intel Corporation Intel(R) Centrino(R) - - 1-0050F204-1
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When the user enters a PIN for a pending Enrollee, e.g., on the web
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UI), hostapd needs to be notified of the new PIN over the control
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interface. This can be done either by using the UNIX domain socket
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-based control interface directly (src/common/wpa_ctrl.c provides
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helper functions for using the interface) or by calling hostapd_cli.
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Example command to add a PIN (12345670) for an Enrollee:
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hostapd_cli wps_pin 53b63a98-d29e-4457-a2ed-094d7e6a669c 12345670
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If the UUID-E is not available (e.g., Enrollee waits for the Registrar
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to be selected before connecting), wildcard UUID may be used to allow the PIN to be used once with any UUID:
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hostapd_cli wps_pin any 12345670
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After this, the Enrollee can connect to the AP again and complete WPS
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negotiation. At that point, a new, random WPA PSK is generated for the
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client device and the client can then use that key to connect to the
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AP to access the network.
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If the AP includes a pushbutton, WPS PBC mode can be used. It is
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enabled by pushing a button on both the AP and the client at about the
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same time (2 minute window). hostapd needs to be notified about the AP
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button pushed event over the control interface, e.g., by calling
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hostapd_cli:
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hostapd_cli wps_pbc
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At this point, the client has two minutes to complete WPS negotiation
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which will generate a new WPA PSK in the same way as the PIN method
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described above.
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