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Communication Security: Wireless • Chapter 4 241

WEP provides for two key sizes: 40-bit and 104-bit.These keys are
concatenated to a 24-bit IV to provide either a 64- or 128-bit key for
encryption.

WEP uses the RC4 stream algorithm to encrypt its data.
802.11 networks use two types of authentication: open system and shared-
key.
There are two types of 802.11 network modes: ad hoc and infrastructure.
Ad hoc 802.11 networks are peer-to-peer in design and can be
implemented by two clients with wireless network cards.The
infrastructure mode of 802.11 uses APs to provide wireless connectivity to
a wired network beyond the AP.

To protect against some rudimentary attacks that insert known text into
the stream to attempt to reveal the key stream,WEP incorporates a
checksum in each frame.Any frame not found to be valid through the
checksum is discarded.

Used on its own,WEP does not provide adequate WLAN security.
WEP must be implemented on every client as well as every AP to be
effective.
WEP keys are user definable and unlimited.They do not have to be
predefined and can and should be changed often.

Despite its drawbacks, you should implement the strongest version of WEP
available and keep abreast of the latest upgrades to the standards.

Wireless communication relies on radio frequencies that are susceptible to
electromagnetic and radio frequency interferences (EMI and RFI). Spread
Spectrum technologies reduce the effects of EMI and RFI.

An Ad-hoc Wireless Network is created when two or more wireless
devices are connected. In an Ad-hoc network there is no AP.
Frequency Hopping Spread Spectrum (FHSS) is used in Bluetooth and
Home RF wireless networks. It transmits RF signals by using rapid
frequency switching. It has a frequency range of 2.4 GHz and has limited
transmission speeds from 1.6 Mbps to 10 Mbps.

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