The 802.11 standard - WEP algorithm

The 802.11 standard taken the security of information issues by marginal and optional way and favoured the WEP algorithm. At the specification of 802.11 it was defined open certification and shared key authentication. The access control in open certification and with shared key authentication are based on WEP encryption and possess of WEP keys.

Achievement of security level offered by wire network with cryptography was the purpose of WEP algorithm inventors. The WEP algorithm based on streaming encription algorithm RC4, within with secret key at about 40 to 104 bites is joined with 24-bite Intializator Vector IV. The final result is that the encode key has 64 or 128 bites lenght (appriopriately WEP 64 or WEP 128), created by this way the row used for encoring M open text and its checksum ICV (Integrity Check Value). There are used a various initialization vectors in order to prevent packages encryption with RC4 algorithm based on the same key. It is counted the checksum ICV of original message M before package sending. Forwarder and receiver share secret key k. The checksum ICV which bases on CRC32 (Cyclic Redundancy Code) and ensures integrity of data transfered is encrypted with the data field M by XOR operation with the key stream. The 24-bite initialize vector IV is sent by open way and makes the part of encrypted transformation, presented at the picture 1.

By default the stations which use the WEP algorithm were co- shared 4 keys (default keys). At the part of frame are assigned two bites for key ID. Distribution of that keys runs by manual way – users of wireless network tape it by themselves.

The WEP protocol were not created by nor security neither cryptography specialists, that is way since after lanched of this protocol it was shown that weak point of RC4 algorithm are present in this case too. In 2001 Scott Fluhrer, Itsik Mantin and Adi Shamir (known as FMS) published well known article about WEP included serious susceptibilities of encrtyped algorithm RC4 to two cases of attacks: attack on key immutability and attack with well known vector initialized IV. The susceptibilities on attacks were used in practice by such tools as the AirSnort program, which are able to perform the WEP keys at base of quite large amount of encrypted packages analyse. With the stage of check integrity is connected with serious weakness of using the CRC32 as checksum algorithm. The CRC32 is often use for transmission errors detecting, however on account of linearity processing it was never thought as criptographically safe algorithm. After that discoveries it was universally accepted, that security level offered by WEP is fit for home users and application without critical meaning only.