The principle of Complete Mediation requires that every access to every object must be checked for authority. This principle explicitly argues against relying on cached permissions, as the state of authorization can change between the time of the initial check and a subsequent access. The scenario describes a system that must validate access rights for all resources and not use a cached matrix precisely because a revoked permission might not be reflected, leading to a security violation. This is the textbook definition of enforcing Complete Mediation.

A. economy of mechanism: This principle advocates for keeping the design as simple and small as possible to facilitate verification, not for how often access checks are performed.

C. separation of privilege: This principle requires that access be granted based on more than one condition or credential, not that every access attempt must be re-validated.

D. least common mechanism: This principle advises minimizing shared resources between users to prevent unintended information paths, which is unrelated to validating every access request.

1. Saltzer

J. H.

& Schroeder

M. D. (1975). The Protection of Information in Computer Systems. Communications of the ACM

18(7)

38-49. In Section I.A.3.b

"Principle of Complete Mediation

" it states

"Every access to every object must be checked for authority... If a mechanism remembers the result of an authority check

it is acting as a cache... If the rights can change

the cache may be incorrect." This directly supports the answer.

2. National Institute of Standards and Technology (NIST). (2018). Systems Security Engineering: Considerations for a Multidisciplinary Approach in the Engineering of Trustworthy Secure Systems (NIST Special Publication 800-160

Vol. 1). In Appendix F.3

"Complete Mediation

" the principle is defined as: "every access to every object must be checked for authority... The checking mechanism should not rely on a previous check."

3. Parno

B.

& Perrig

A. (2014). 6.858 Computer Systems Security

Fall 2014 Lecture Notes. Massachusetts Institute of Technology: MIT OpenCourseWare. In Lecture 2

Section 4

"Secure design principles (Saltzer & Schroeder)

" Complete Mediation is summarized as: "Check every access. Don't cache results of a check."