128 bit WEP devices can be used with 40 or 64 bit WEP devices aslong as the device driver has a way to set the lower encryptionlevel. The encryption level is determined by the encryption keylength. If a device is capable of 128 bit encryption, it isinherently capable of 40 bit, unless the vendor decides for somereason not allow the lower encryption level.
64 bit WEP is the same as 40 bit WEP!
The lower level of WEP encryption uses a 40 bit 10 hex charactersecret key set by the user and a 24 bitInitialization Vector which is not under usercontrol. Some vendors refer to this level of WEP as 40 bit, othersas 64 bit. Either way, they´re the same encryption level andcan interoperate.
The higher level of WEP encryption, commonly referred to as 128bit WEP, actually uses a 104 bit , 26 hex character, secretkey , set by the user and a 24 bit InitializationVector which is not under user control.