We will review Saltzer and Schroeder’s security principles of (1) complete mediation; (2) least privilege; and (3) privilege separation. We will also briefly review security tag (or label) propagation. In security tag propagation, a set of rules are used to compute the security attributes of each computation. For example, C = A + B, where A is trusted and B is not trusted. The result C is labeled not trusted. We do not want to use the untrusted result, C, to control any shared computer resource. Using an untrusted result to control (or manage) a shared resource would leave a cybersecurity vulnerability. We illustrate how security tag (or label) propagation can be implemented in the two level security tag architecture in the OS Friendly Microprocessor Architecture. We describe the benefits of using two level security tags for security tag computations.