ZyXEL Communications P-870HW-51A V2, Руководство пользователя

Страница: 77 / 150

Chapter 7 Wireless LAN
P-870HW-51a v2 User’s Guide
77
Wireless Security
By their nature, radio communications are simple to intercept. For wireless data networks, this
means that anyone within range of a wireless network without security can not only read the
data passing over the airwaves, but also join the network. Once an unauthorized person has
access to the network s/he can either steal information or introduce malware (malicious
software) intended to compromise the network. For these reasons, a variety of security
systems have been developed to ensure that only authorized people can use a wireless data
network, or understand the data carried on it.
These security standards do two things. First, they authenticate. This means that only people
presenting the right credentials (often a username and password, or a “key” phrase) can access
the network. Second, they encrypt. This means that the information sent over the air is
encoded. Only people with the code key can understand the information, and only people who
have been authenticated are given the code key.
These security standards vary in effectiveness. Some can be broken, such as the old Wired
Equivalent Protocol (WEP). Using WEP is better than using no security at all, but it will not
keep a determined attacker out. Other security standards are secure in themselves but can be
broken if a user does not use them properly. For example, the WPA-PSK security standard is
perfectly secure if you use a long key which is difficult for an attacker’s software to guess - for
example, a twenty-letter long string of apparently random numbers and letters - but it is not
very secure if you use a short key which is very easy to guess - for example, a three-letter word
from the dictionary.
Because of the damage that can be done by a malicious attacker, it’s not just people who have
sensitive information on their network who should use security. Everybody who uses any
wireless network should ensure that effective security is in place.
A good way to come up with effective security keys, passwords and so on is to use obscure
information that you personally will easily remember, and to enter it in a way that appears
random and does not include real words. For example, if your mother owns a 1970 Dodge
Challenger and her favorite movie is Vanishing Point (which you know was made in 1971)
you could use “70dodchal71vanpoi” as your security key.
Signal Problems
Because wireless networks are radio networks, their signals are subject to limitations of
distance, interference and absorption.
Problems with distance occur when the two radios are too far apart. Problems with
interference occur when other radio waves interrupt the data signal. Interference may come
from other radio transmissions, such as military or air traffic control communications, or from
machines that are coincidental emitters such as electric motors or microwaves. Problems with
absorption occur when physical objects (such as thick walls) are between the two radios,
muffling the signal.
7.3 Before You Begin
Before you start using these screens, ask yourself the following questions. See Section 7.2 on
page 76 if some of the terms used here do not make sense to you.