Implementation of the SILC Key Exchange Protocol (SKE). The SKE protocol
 is used to negotiate secret key material between two parties, to be used
 as session key or some other key. For example, when client connects to
 server SKE is performed to exchange public keys, and to generate the key
 that is then used as session key. Two clients can execute SKE as well
 two create secret key material for securing for example file transfer
 stream.

 SKE is based on Diffie-Hellman, and it derives its functionality from
 SSH2 Key Exchange protocol, OAKLEY Key Determination protocol and
 Station-To-Station (STS) protocols.

 This SKE implementation provides easy interface for application
 that wants to use SKE. In fact, the interface is designed to be 
 application independent, and does not expect that the application using
 SKE would actually relate in any way to SILC. Hence, the interface
 can be used in any kind of application needing to perform key exchange
 protocol with two parties. The network connection is also handled
 outside the SKE interface. For the interface application must provide
 a packet sending function which SKE library can call when it wants
 to send packet to the remote host. The actual network connection
 therefore is handled in the application and not by the SKE library.

 The protocol has initiator and responder. The initiator is the one
 that starts the protocol, and the responder is the one that receives
 negotiation request. The protocol has phases, and the interface is
 split into several phases that the application may call when
 needed. Heavy operations has been splitted so that application may
 call next phase with a timeout to give processing times to other
 things in the application. On the other hand, if application does
 not care about this it may call the phases immediately without any
 timeout.