Trust Computing Base (TCB)

This is part of the computing system that absolutely must be trustworthy if we are going to get anything done. This usage of trusted may seem conterintuitive: We do not trust the TCB because it's worthy of trust but rather because we have no choice. consequently, it's important both to know what the TCB is and to keep it as small as possible. This way, we have more assuarance that what's trusted is also trustworthy. The TCB is defined also indirectly as security perimeter that separate it from the rest of the system. The reference monitor is somtimes called security kernel. The user had better be sure whether he is communicating to the TCB. Trusted path denotes a mechanism through which the user can do this. A secure attention key is the mechanism used by user to establish the channel.