There are three types of accesses or logins that can be discussed in a network. The first is the local login. This is where the user authenticates himself to the local system (called the client here), usually by supplying a password (although interest in using smartcards/tokens is growing). The second type of login is the remote login. This is when the user from a local system logs into a remote system. For example a user might use a telnet service to login to a remote system. The third type of access that requires authentication is a client/server request. An example of this is when a user mounts on his local machine a remote file system and makes requests to access those files. The protocols used for each of these accesses will be examined for both Kerberos and Secure RPC.
Woo [WL92] defines a protocol as a ``precisely defined sequence of
communication and computation steps. A communication step
transfers messages from one principal (sender) to another
principal (receiver), while a computation step updates a
principal's internal state. Two distinct states can be
identified upon protocol termination, one signifying successful
authentication and the other failure''. The following format is
used to describe the protocols for each system. A communication
step ``U 
H : username'' defines that a user (U) sends to a host
(H) a password. A computation step ``H: compute oneway(password)''
defines that a host computes a one-way function of a password.