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Perils of the Ether
Joseph Ritchey


The idea of a wireless world is great. I would like nothing better than to be able to connect to the Internet from anywhere. We are still a few years away from having the infrastructure for anywhere connectivity, but before Wi-Fi can reach that level security issues are going to have to be addressed.

WEP (Wired Equivalent Privacy) is the base security for the 802.11 standard. WEP has three main goals: Confidentiality, Access control and Data Integrity. In a WEP enabled device, the wireless NIC encrypts the payload (frame body and CRC) of each 802.11 frame before transmission using an RC4 stream cipher The receiving station, such as an access point or another radio NIC, performs decryption upon arrival of the frame. As a result, 802.11 WEP only encrypts data between 802.11 stations. Once the frame enters the wired side of the network, such as between access points, WEP no longer applies.

As part of the encryption process, WEP prepares a key schedule ("seed") by concatenating the shared secret key supplied by the user of the sending station with a random-generated 24-bit initialization vector (IV). WEP includes the IV in the clear (unencrypted) within the first few bytes of the frame body. The receiving station uses this IV along with the shared secret key supplied by the user of the receiving station to decrypt the payload portion of the frame body.

WEP specifies a shared key to encrypt and decrypt the data. Some vendors also include 128 bit keys (know as "WEP2") in their products. With WEP, the receiving station must use the same key for decryption. Each radio NIC and access point, therefore, must be manually configured with the same key.

With having to manually configure each NIC with the encryption key problems arise. If the network admin wants to change the encryption key, then the admin has to change the key on all the systems manually.WEP biggest drawback is not in the RC4 cipher, but the 24-bit initialization vector. WEP eventually uses the same IV for different data packets. If a cracker collects enough frames based on the same IV, that cracker can eventually discover the share key.

802.11 doesn't provide any support for mechanisms that allow the exchange of keys among stations. As a result, network admins generally use the same keys for weeks, months, and even years. This permits crackers to monitor and crack into WEP-enabled networks.

The catch-22 of wireless networks is the unlicensed spectrum that they use. The most popular wireless spectrum currently used by Wi-Fi is the 2.4Ghz band. The 2.4Ghz band allows ordinary folks to use this radio frequency for residential application like cordless phones, microwaves, etc. All of these other devices using the 2.4Ghz band create noise, that interferes with the quality of WLAN signals. Newer Wi-Fi devices will eventually use the 5 and 5.4Ghz bands, because there is less noise to contend with and larger bandwidth. Additional because Wi-Fi networks are so easily disrupted by noise a malicious person could disrupt a Wi-Fi network. A Wi-Fi network could conceivably be jammed with just a cordless phone. By creating enough noise a malicious individual could render the network unusable.

Comments to: Joseph Ritchey


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