Brewer-Nash model

Brewer-Nash, also called the Chinese Wall model, exists to prevent conflicts of interest. Picture a consultancy serving two competing banks. Before an analyst opens any file, they may access either client. The moment they read Bank A’s data, a wall goes up: Bank B’s dataset, and everything else in that conflict-of-interest class, becomes off limits for them.

Its distinguishing feature, and the reason the exam loves it, is that access rights are dynamic. Every other model in Domain 3 evaluates a fixed policy: Bell-LaPadula compares static clearances and classifications, and Clark-Wilson checks a fixed set of access triples. Brewer-Nash is the only one where your history changes your permissions. It effectively enforces a time-based flavour of separation of duties across client boundaries. The Brewer-Nash guide covers the formal rules.

Exam relevance: three trigger phrases map straight to Brewer-Nash: “conflict of interest”, “Chinese Wall”, and “access depends on previous access”. It is the go-to answer for consultancies, law firms, and financial institutions handling competing clients. If the scenario’s permissions never change, it is not Brewer-Nash.