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Standard 64-bit WEP uses a 40 bit key (also known as WEP-40), which is concatenated with a 24-bit initialization vector (IV) to form the RC4 traffic key. At the time that the original WEP standard was being drafted, U.S. Government export restrictions on cryptographic technology limited the key size. Once the restrictions were lifted, all of the major manufacturers eventually implemented an extended 128-bit WEP protocol using a 104-bit key size (WEP-104).
A 128-bit WEP key is almost always entered by users as a string of 26 hexadecimal (base 16) characters (0-9 and A-F). Each character represents four bits of the key. 26 digits of four bits each gives 104 bits; adding the 24-bit IV produces the final 128-bit WEP key.
A 256-bit WEP system is available from some vendors, and as with the 128-bit key system, 24 bits of that is for the IV, leaving 232 actual bits for protection. These 232 bits are typically entered as 58 hexadecimal characters. (58 × 4 = 232 bits) + 24 IV bits = 256-bit WEP key.
Key size is not the only major security limitation in WEP.[10] Cracking a longer key requires interception of more packets, but there are active attacks that simulate the necessary traffic. There are other weaknesses in WEP, including the possibility of IV collisions and altered packets,[7] that are not helped at all by a longer key.
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