mediate that every instance of the (pseudo)rand sequence router; however, reasonably secure communications over would then be identical; it wouldn't be very hard for an the Internet can be managed with the aid of the Secure eavesdropper to reconstruct the cipher stream once Sockets Layer (SSL), another encrypted link between the a large number of packets, many containing known user of a web site and the site server. plaintext such as the contents of standard Internet It was apparent to the developers of wireless data packets, had been intercepted. Therefore, to avoid using devices that the wireless medium is more subject to the same cipher stream for every packet while also interception and eavesdropping than the wired medium, avoiding the complexity of exchanging a new key be- though they were also aware of the many vulnerabilities tween the sender and receiver each time a packet needs in existing wired networks. They therefore attempted to to be transmitted, the WEP algorithm uses an initiali- produce a security mechanism that would emulate the zation vector (IV): 24 additional bits that are prepended modest privacy level obtained with physically controlled to the 48-bit secret key to form the seed for the random Ethernet wired ports in a fashion that was simple to number generator. In this fashion, each new packet gets RC4 random number generator Initialization vector (IV) shared secret key 24 bits 48 bits cipher stream data stream Initialization vector encrypted data Figure 5.1-21 Simplified schematic of WEP encryption. CHAPTER 5.1 Wireless local area networks a new seed for the random number generator and thus Obviously, it is even better to obtain the shared key a unique cipher stream. and thus encrypt and decrypt freely than to extract a few In addition to security from interception, a secure cipher streams. Attacks to find the shared key can exploit communications system should provide some means of the fact that the key is defined as a bit stream, but human authentication: each side should have some conf