STU-III-multilevel secure computer interface

The interconnection of the STU-III (Secure Telephone Unit) and a multilevel secure (MLS) host computer is a layered composition of systems. The composed systems that form the layers result from the connection processing done to establish the host-to-host link. To ensure that the system represented by each composed layer is consistent with the security policy, an additional agent must be added to the host´s trusted computing base (TCB). This agent manages the STU-III data port interface and undertakes the coordination necessary to ensure that the security state is consistent between each layer; this coordination includes the security coordination between the two host TCBs and the eventual establishment of the remote session. The agent is implemented as a trusted process and is invisible to a process requesting connection to another host. This implementation allows for the greatest flexibility in the use of hardware at some additional cost in complexity