Abstract :
802.11 wireless LAN security or lack of
it remains at the top of most LAN administrators list of worries. The security for 802.11 is provided by
the Wired Equivalency Policy (WEP) at the MAC layer for authentication and
encryption The original goals of IEEE in defining WEP was to provide the
equivalent security of an "unencrypted" wired network. The difference is the
wired networks are somewhat protected by physical buildings they are housed in.
On the wireless side, the same physical layer is open in the airwaves.
WEP provides authentication to the
network and encryption of transmitted data across the network. WEP can be set either to either an open
network or utilizing a shared key system. The shared key system used with WEP
as well as the WEP encryption algorithm are the most widely discussed
vulnerabilities of WEP. Several manufacturers' implementations introduce additional vulnerabilities to the
already beleaguered standard.
WEP uses the RC4 algorithm known as a
stream cipher for encrypting data. Several manufacturers tout larger 128-bit
keys, the actual size available is 104 bits. The problem with the key is not the length, but lies within the
actual design of WEP that allows secret identification. A paper written by
Jesse Walker, "Unsafe at any key length" provides insight to the
specifics of the design vulnerabilities and explains the exploitation of WEP.
1) The wireless station begins the
process by sending an authentication frame to the AP it is trying to associate
with.
2) The receiving AP sends a reply to
the wireless station with its own authentication frame containing 128 octets of challenge text.
3) The wireless station then encrypts
the challenge text with the shared key and sends the result back to the AP.
4) The AP then decrypts the encrypted
challenge using the same shared key and compares it to the original challenge
text. If the there is a match, an ACK is sent back to the wireless station,
otherwise a notification is sent back rejecting the authentication.
Wireless LAN Deployment
The biggest difference in deployment of Wireless LANs over their
wired counterpart are due to the physical layer operates in the airwaves and is
affected by transmission and reception factors such as attenuation, radio
frequency (RF) noise and interference, and building and structural interference.
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