In the previous chapter, we have seen how a given device can be properly and un-ambiguously designated by a name or an address. In this chapter, we will explain how two wireless devices can securely identify each other and get ready to communicate securely with each other; in other words, we will see how they can perform authentication and key establishment.

Authentication and key establishment are strongly related to each other, because of their mutual dependency: once two (or more) entities have authenticated each other, they can usually establish a key, in order to secure their future communications; conversely, an already established key can be very useful to perform future authentication.

These two operations are considered to be among the most fundamental (if not the two most fundamental) mechanisms of network security. As a result, a huge number of protocols have been proposed (and a sizeable number of them have already been standardized and implemented) in order to support authentication and key establishment in (wired) networks. The choice of a protocol depends notably on the role of the trusted server (if any), on whether the key is established by one of the principals (and then transported to the other(s)) or agreed among the principals, and on the underlying cryptographic mechanisms (symmetric or asymmetric).