185 lines
6.9 KiB
Plaintext
185 lines
6.9 KiB
Plaintext
wpa_supplicant and Wi-Fi Protected Setup (WPS)
|
|
==============================================
|
|
|
|
This document describes how the WPS implementation in wpa_supplicant
|
|
can be configured and how an external component on the client (e.g.,
|
|
management GUI) is used to enable WPS enrollment and registrar
|
|
registration.
|
|
|
|
|
|
Introduction to WPS
|
|
-------------------
|
|
|
|
Wi-Fi Protected Setup (WPS) is a mechanism for easy configuration of a
|
|
wireless network. It allows automated generation of random keys (WPA
|
|
passphrase/PSK) and configuration of an access point and client
|
|
devices. WPS includes number of methods for setting up connections
|
|
with PIN method and push-button configuration (PBC) being the most
|
|
commonly deployed options.
|
|
|
|
While WPS can enable more home networks to use encryption in the
|
|
wireless network, it should be noted that the use of the PIN and
|
|
especially PBC mechanisms for authenticating the initial key setup is
|
|
not very secure. As such, use of WPS may not be suitable for
|
|
environments that require secure network access without chance for
|
|
allowing outsiders to gain access during the setup phase.
|
|
|
|
WPS uses following terms to describe the entities participating in the
|
|
network setup:
|
|
- access point: the WLAN access point
|
|
- Registrar: a device that control a network and can authorize
|
|
addition of new devices); this may be either in the AP ("internal
|
|
Registrar") or in an external device, e.g., a laptop, ("external
|
|
Registrar")
|
|
- Enrollee: a device that is being authorized to use the network
|
|
|
|
It should also be noted that the AP and a client device may change
|
|
roles (i.e., AP acts as an Enrollee and client device as a Registrar)
|
|
when WPS is used to configure the access point.
|
|
|
|
|
|
More information about WPS is available from Wi-Fi Alliance:
|
|
http://www.wi-fi.org/wifi-protected-setup
|
|
|
|
|
|
wpa_supplicant implementation
|
|
-----------------------------
|
|
|
|
wpa_supplicant includes an optional WPS component that can be used as
|
|
an Enrollee to enroll new network credential or as a Registrar to
|
|
configure an AP. The current version of wpa_supplicant does not
|
|
support operation as an external WLAN Management Registrar for adding
|
|
new client devices or configuring the AP over UPnP.
|
|
|
|
|
|
wpa_supplicant configuration
|
|
----------------------------
|
|
|
|
WPS is an optional component that needs to be enabled in
|
|
wpa_supplicant build configuration (.config). Here is an example
|
|
configuration that includes WPS support and Linux wireless extensions
|
|
-based driver interface:
|
|
|
|
CONFIG_DRIVER_WEXT=y
|
|
CONFIG_EAP=y
|
|
CONFIG_WPS=y
|
|
|
|
|
|
WPS needs the Universally Unique IDentifier (UUID; see RFC 4122) for
|
|
the device. This is configured in the runtime configuration for
|
|
wpa_supplicant (if not set, UUID will be generated based on local MAC
|
|
address):
|
|
|
|
# example UUID for WPS
|
|
uuid=12345678-9abc-def0-1234-56789abcdef0
|
|
|
|
The network configuration blocks needed for WPS are added
|
|
automatically based on control interface commands, so they do not need
|
|
to be added explicitly in the configuration file.
|
|
|
|
WPS registration will generate new network blocks for the acquired
|
|
credentials. If these are to be stored for future use (after
|
|
restarting wpa_supplicant), wpa_supplicant will need to be configured
|
|
to allow configuration file updates:
|
|
|
|
update_config=1
|
|
|
|
|
|
|
|
External operations
|
|
-------------------
|
|
|
|
WPS requires either a device PIN code (usually, 8-digit number) or a
|
|
pushbutton event (for PBC) to allow a new WPS Enrollee to join the
|
|
network. wpa_supplicant uses the control interface as an input channel
|
|
for these events.
|
|
|
|
If the client device has a display, a random PIN has to be generated
|
|
for each WPS registration session. wpa_supplicant can do this with a
|
|
control interface request, e.g., by calling wpa_cli:
|
|
|
|
wpa_cli wps_pin any
|
|
|
|
This will return the generated 8-digit PIN which will then need to be
|
|
entered at the Registrar to complete WPS registration. At that point,
|
|
the client will be enrolled with credentials needed to connect to the
|
|
AP to access the network.
|
|
|
|
|
|
If the client device does not have a display that could show the
|
|
random PIN, a hardcoded PIN that is printed on a label can be
|
|
used. wpa_supplicant is notified this with a control interface
|
|
request, e.g., by calling wpa_cli:
|
|
|
|
wpa_cli wps_pin any 12345670
|
|
|
|
This starts the WPS negotiation in the same way as above with the
|
|
generated PIN.
|
|
|
|
|
|
If the client design wants to support optional WPS PBC mode, this can
|
|
be enabled by either a physical button in the client device or a
|
|
virtual button in the user interface. The PBC operation requires that
|
|
a button is also pressed at the AP/Registrar at about the same time (2
|
|
minute window). wpa_supplicant is notified of the local button event
|
|
over the control interface, e.g., by calling wpa_cli:
|
|
|
|
wpa_cli wps_pbc
|
|
|
|
At this point, the AP/Registrar has two minutes to complete WPS
|
|
negotiation which will generate a new WPA PSK in the same way as the
|
|
PIN method described above.
|
|
|
|
|
|
If the client wants to operation in the Registrar role to configure an
|
|
AP, wpa_supplicant is notified over the control interface, e.g., with
|
|
wpa_cli:
|
|
|
|
wpa_cli wps_reg <AP BSSID> <AP PIN>
|
|
(example: wpa_cli wps_reg 02:34:56:78:9a:bc 12345670)
|
|
|
|
|
|
Scanning
|
|
--------
|
|
|
|
Scan results ('wpa_cli scan_results' or 'wpa_cli bss <idx>') include a
|
|
flags field that is used to indicate whether the BSS support WPS. If
|
|
the AP support WPS, but has not recently activated a Registrar, [WPS]
|
|
flag will be included. If PIN method has been recently selected,
|
|
[WPS-PIN] is shown instead. Similarly, [WPS-PBC] is shown if PBC mode
|
|
is in progress. GUI programs can use these as triggers for suggesting
|
|
a guided WPS configuration to the user. In addition, control interface
|
|
monitor events WPS-AP-AVAILABLE{,-PBC,-PIN} can be used to find out if
|
|
there are WPS enabled APs in scan results without having to go through
|
|
all the details in the GUI. These notification could be used, e.g., to
|
|
suggest possible WPS connection to the user.
|
|
|
|
|
|
wpa_gui
|
|
-------
|
|
|
|
wpa_gui-qt4 directory contains a sample GUI that shows an example of
|
|
how WPS support can be integrated into the GUI. Its main window has a
|
|
WPS tab that guides user through WPS registration with automatic AP
|
|
selection. In addition, it shows how WPS can be started manually by
|
|
selecting an AP from scan results.
|
|
|
|
|
|
Credential processing
|
|
---------------------
|
|
|
|
By default, wpa_supplicant processes received credentials and updates
|
|
its configuration internally. However, it is possible to
|
|
control these operations from external programs, if desired.
|
|
|
|
This internal processing can be disabled with wps_cred_processing=1
|
|
option. When this is used, an external program is responsible for
|
|
processing the credential attributes and updating wpa_supplicant
|
|
configuration based on them.
|
|
|
|
Following control interface messages are sent out for external programs:
|
|
|
|
WPS-CRED-RECEIVED <hexdump of Credential attribute(s)>
|
|
For example:
|
|
<2>WPS-CRED-RECEIVED 100e006f10260001011045000c6a6b6d2d7770732d74657374100300020020100f000200081027004030653462303435366332363666653064333961643135353461316634626637313234333761636664623766333939653534663166316230323061643434386235102000060266a0ee1727
|