At the present time there is a rapid growth in compute r communications associated with terminal-based, multi-use r computer systems, and in networks of computers [1,2,3] . Nearly all such systems communicate, process, or store informatio n which is considered private or proprietary by their owner s and users, or which must be safeguarded from unauthorize d access as required by law . Furthermore, associated terminals , telecommunication systems, communication processors, an d computers must be protected from intruders that may seek t o alter programs or data in the system, or to disrupt the services provided . These threats are real, since it is no t difficult to intercept transmissions in telecommunicatio n networks [4,5], and it is possible to connect illicit terminals (or even computers) into the system for the purpose s of "managing" the normal terminal-computer communications , masquerading as a legitimate user, or simply making the syste m unavailable to others [5,7] .The protection of a computer communication system agains t the various threats involves :(1) identification,and authentication of the identity, (2) controlled access to computer s and their data bases, and (3) protection of the data i n transit in the telecommunication system . Associated with