work. However, the transmission range and number of participating stations are
greatly limited in ad-hoc networks. They also do not support WPA authentication.
If you intend to use WPA security, you should not use Ad-Hoc_Mode.
Master Mode
In master mode your network card is used as the access point. It works only if your
WLAN card supports this mode. Find out the details of your WLAN card on
http://linux-wless.passys.nl.
24.3 Authentication
Because a wireless network is much easier to intercept and compromise than a wired
network, the various standards include authentication and encryption methods. In the
original version of the IEEE 802.11 standard, these are described under the term WEP
(Wired Equivalent Privacy). However, because WEP has proven to be insecure (see
Section 24.6.3, “Security” (page 445)), the WLAN industry (joined under the name Wi-
Fi Alliance) has dened an extension called WPA, which is supposed to eliminate the
weaknesses of WEP. The later IEEE 802.11i standard includes WPA and some other
authentication and encryption methods. IEEE 802.11i is also referred to as WPA2, be-
cause WPA is based on a draft version of 802.11i.
To make sure that only authorized stations can connect, various authentication mecha-
nisms are used in managed networks:
None (Open)
An open system is a system that does not require authentication. Any station can
join the network. Nevertheless, WEP encryption can be used, see Section 24.4,
“Encryption” (page 434).
Shared Key (according to IEEE 802.11)
In this procedure, the WEP key is used for the authentication. However, this proce-
dure is not recommended, because it makes the WEP key more susceptible to at-
tacks. All an attacker needs to do is to listen long enough to the communication
between the station and the access point. During the authentication process, both
sides exchange the same information, once in encrypted form and once in unen-
crypted form. This makes it possible for the key to be reconstructed with suitable
tools. Because this method makes use of the WEP key for the authentication and
for the encryption, it does not enhance the security of the network. A station that
has the correct WEP key can authenticate, encrypt, and decrypt. A station that does
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