ZyXEL Communications P-334WT Support Notes page 188

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Setup WEP
Wired Equivalent Privacy)
Introduction
Setting up the Access Point
Setting up the Station
Introduction
The 802.11 standard describes the communication that occurs in wireless LANs.
The Wired Equivalent Privacy (WEP) algorithm is used to protect wireless communication from eavesdropping, because wireless
transmissions are easier to intercept than transmissions over wired networks, and wireless is a shared medium, everything that is
transmitted or received over a wireless network can be intercepted.
WEP relies on a secret key that is shared between a mobile station (e.g. a laptop with a wireless Ethernet card) and an access
point (i.e. a base station). The secret key is used to encrypt packets before they are transmitted, and an integrity check is used to
ensure that packages are not modified during the transition. The standard does not discuss how the shared key is established. In
practice, most installations use a single key that is shared between all mobile stations and access points APs.
WEP employs the key encryption algorithm, Ron's Code 4 Pseudo Random Number Generator (RC4 PRNG). The same key is
used to encrypt and decrypt the data.
WEP has defences against this attack. To avoid encrypting two cipher texts with the same key stream, an Initialisation Vector
(IV) is used to augment the shared WEP key (secret key) and produce a different RC4 key for each packet, the IV is also
included in the package. WEP key (secret key) are available in two types, 64-bits and 128-bits. Many times you will see them
referenced as 40-bits and 104-bits instead. The reson for this misnomer is that the WEP key ( 40/104 bits ) is concatenated with
the initialisation vector ( 24 bits ) resulting in a 64/128 bit total key size.