WEP is the encryption standard that comes with WiFi LANs. It
uses RC4 encryption, which is the same as that used by the
security built into standard web browsers (SSL). One might
think, therefore, that it is sufficiently tried and tested to be
trusted. Well, there's not a great deal wrong with RC4 -- but
there is a great deal wrong with its implementation within WiFi.
Put simply, it should not be used in this manner. (Technically,
it is a stream cipher being used where a stream cipher should
not be used. A block cipher would have been better for WLANs.
But RC4 was easy and cheap to implement - and with 40 bit keys
it was not subject to the then existent US export laws.)
Problems with WEP were known at the end of year 2000. But in
summer 2001, the well-known cryptographers Fluhrer, Mantin and
Shamir (the 'S' of RSA) published a new paper in which “we show
that RC4 is completely insecure in a common mode of operation
which is used in the widely deployed Wired Equivalent Privacy
protocol (WEP, which is part of t