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Security Fundamentals & Crypto · Intermediate

Complete Mediation

Design principle that every access to every object must be checked for authorization every time.

Definition

Complete mediation requires that access checks are not bypassed or cached in ways that allow stale decisions. It is the foundation of the reference monitor concept. Caching permissions without revalidation can violate it when rights are revoked.

Example

A file server checks permissions on each read request instead of only when the file is first opened.

Exam tip

Linked to the reference monitor, which must be always invoked, tamperproof, and verifiable.

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