Which of the following rated systems of the Orange book has mandatory protection of the TCB?

A-rated systems (A1) provide the highest level of assurance, built upon B3, but B-rated systems are where mandatory protection of the TCB is first explicitly required and enforced.

The B-rated (B1, B2, B3) divisions of the Orange Book, specifically the B1-labeled systems, introduce the requirement for mandatory protection of the Trusted Computing Base (TCB). These systems require a formally defined security policy and are architecturally designed to provide relatively strong protection for sensitive information, moving beyond discretionary access control to include mandatory access controls.

D-rated systems represent minimal protection, often failing to meet the requirements for higher ratings.

C-rated systems (C1, C2) focus on discretionary protection and accountability, but do not mandate the same level of TCB protection as B-rated systems.