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Standards of Wireless LAN
Just like in other standards IEEE 802.x (ex. 802.3 Ethernet), standard 802.11 defines the physical layer (PHY - Physical Medium Layer) and the sub-layer for medium access control. Pic. 2 presents the basic model of reference of IEEE 802.11. In the picture-in-question the physical layer was divided into two sub-layers. The sub-layer dependent on the medium (PMD - Physical Medium Dependent) co-operates with the media characteristic of a wireless net, i.e. DSSS or FHSS. It also determines the data receipt and dispatch methods (ex. modulation, coding). The second sub-layer of the physical layer, i.e. Physical Layer Convergence Procedure – PLCP, defines the method of projection of a data unit of MAC sub-layer protocol into the package format convenient for PMD sub-layer. On the data link layer a sub-layer for medium access control was distinguished, which determines the basic medium access mechanism for numerous stations. It can realize fragmentations and encoding of data packages.
SAFETY
Due to the general-availability of wireless networks, wireless system designers have to provide a proper level of information protection by activating proper services increasing safety of IEEE 802.11 networks. IEEE 802.11 standard offers the following authentication methods:
a) OSA (Open System Authentication) - it is a default authentication method that consists in casual, not-encoded request of joining another station or access point;
b) SKA (Shared Key Authentication) is an optional authentication method, offering considerably higher level of security than OSA method. It consists in every station having to be equipped with an implemented WEP protocol.
WEP Protocol is based on a data encoding algorithm with application of RC4 PRNG (Ron's Code 4 Pseudo Random Number Generator), which is used by all of the clients` stations and access points existing in a wireless net for encoding and decoding of the data. The key is stored in every wireless device that participates in data exchange. The IEEE 802.11 standard does not determine any key management protocol, therefore the WEP keys have to managed by the administrator in the network or with application of mechanisms provided by companies producing wireless devices. WEP protocol enables usage of a 40-bit encoding key, as well as a much stronger 104-bit key. The encoding key is combined with a 24-bit initialization vector, IV, as a result of which a 64-or 128-bit key is received. The key-in-question is given on entrance of PRNG, which, on this basis, generates a pseudo random key sequence. The received sequence is used for data encoding and, in particular, for performing the XOR (eXclusive OR) function. It is used for protection of a 32-bit Integrity Check Value vector, ICV, as well as of the data itself.
At present, programs such as Airsnort, or WEPCrack, by using a discovered error in the algorithm, can find a 128-bit key after an hour in favorable conditions, i.e. when a considerable number of data is dispatched.
See also: Wireless Local Area Network Technology