In The Beginning
In early 2002, I concluded that having a laptop was probably a
good idea. And a few months later, having a wireless link at home
seemed an even better idea. Trailing a long cable around behind
the laptop just wasn't all that great an idea. Thus began the saga
of exploring the 802.11b networking scene.
I was aware of the security concerns with a wireless link. As the
signals are broadcast, anybody within receiving distance can
receive the transmissions, and/or use the network. While the
snooping can be defeated by using ssh or other encryption methods,
illicit use of the network (and specifically the connection to
the internet) is more difficult. So the first step was to look
at what the hardware has on offer.
There are two basic styles of networking for a small area (read home)
environment. One is
which involves just PCs with net cards connecting to one another.
The second is
which uses an
as a wireless hub and connection to a wired network. (Access points
may be configured to connect to other access points too, but I
don't need that.) As connection to the wired network was the
most important requirement, the managed mode of operation was
the style to adopt.
So there is a need for an acess point, and a wireless card for the
laptop. But the access point needs to be plugged into something,
so a net card was also required. For reasons to be explained later,
the access point is not connected directly to the wired network.
Access and Privacy
As wireless is a broadcast system, anybody nearby can receive
the transmissions. There are two major consequences of this:-
The first is a problem of authentication - allowing only authorised
access to the network. The second is one of privacy. The 802.11
standards have facilities to control both of these.
Access is provided to the internet and/or internal network
Wireless traffic can be monitored/snooped
Privacy requires some form of encryption, to make the data appear
garbled without possessing the secret key. In the 802.11 world,
this is implemented via WEP - Wired Equivalent Privacy. The same secret
key is required at each end of the link. Which means that a key
is set at the access point, and each legitimate user needs to also
have a copy of the key.
WEP is available in 3 key lenghts - the number of bits used in the key.
In a good system, the longer the key length, the more secure the
system is against brute force attacks. A brute force attack is
enumerating all possible keys until the garbled messages appear in
the clear. The WEP key length can be set at 64, 128 or 256 bits.
The 256 bit length is not as commonly supported as the other two.
The 802.11 specification breaks the key length into two parts.
Twenty four of the bits are "factory set", and the remaining ones
are set by the administrator and distributed to authorised users.
There are several methods to control authorised access to the
access point. These are
MAC address (the 48 bit globally unique ethernet hardware address)
filtering restricts which stations the access point will accept,
or reject, depending upon its configuration.
MAC address filtering
The ESSID is an up to 32 character string used to provide a name
to the network. The idea is that in an area where independent
network signals overlap, the name will allow stations to connect
with their network.
The shared secret is just that - a key which both ends know,
and which is used during the initial exchange when a station is
creating a connection to the base station. If the key tests
pass, the station is accepted as legitimate.
Unfortunately, the implementation of WEP is flawed, and it is
quite easy to determine the key. There are a number of programs
available on the net to do this. It's a topic to be covered later.
Version: $Revision: 1.3 $;
Updated at 15:47 EST on Tue Apr 11, 2006
Copyright (C) 2002 - 2006, Lindsay Harris