Chapter 8 — Security architecture basics
Lesson map
Lesson 08 published. Map, example, EX022.
flowchart TD
N0["Learning outcomes"]
N1["8.1 Architecture for a small firm"]
N2["8.2 Design principles"]
N3["8.3 A zone diagram"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4
N4 --> EX["Worked example"]
EX --> Q["Exercise EX022"]
Logical drawing
flowchart LR
N0["Learning outcomes"]
N1["8.1 Architecture for a small firm"]
N2["8.2 Design principles"]
N3["8.3 A zone diagram"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4 --> Q["EX022"]
[Learning outcomes]
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v
[8.1 Architecture for a small firm]
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v
[8.2 Design principles]
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v
[8.3 A zone diagram]
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v
[Synthesis]
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v
[Worked example] --> [Exercise EX022]
Learning outcomes
You will (1) explain what security architecture means for a small firm; (2) apply core design principles; (3) draw a simple zone diagram.
8.1 Architecture for a small firm
Ruth explains that security architecture is the overall arrangement of protections across systems, not a single device. For Brightwater, it answers questions such as which systems can talk to which, where identities are checked, where data is stored and how services recover after failure. Even a four-depot company benefits from writing this down, because decisions made one at a time tend to contradict each other. A simple architecture gives Sam a reference when vendors propose new connections. The written version also helps new IT staff understand past choices without relying on memory.
8.2 Design principles
Tomás applies classic principles from Saltzer and Schroeder (1975). Least privilege: each role gets only what it needs. Fail-safe defaults: new devices join a quarantine network until approved. Economy of mechanism: one identity service rather than separate logins per application. Complete mediation: the tracking service checks permissions on every request, not just at sign-in. Separation of privilege: changes to bank details in finance need two people. He links each principle to a specific Brightwater decision so it becomes practical. Ruth asks him to mark where two principles pull in different directions.
8.3 A zone diagram
Tomás draws a diagram of the main depot with four zones: office, operations devices such as scanners and printers, the conveyor control system and guest wireless. Arrows show permitted flows: operations devices reach the cloud tracking service; the conveyor accepts connections only from the vendor's support gateway; guests reach only the internet. The diagram fits on one page. Sam pins it next to the network cabinet so anyone making changes can check whether a new connection fits the design before plugging in.
Worked example
Tomás explains architecture for a small firm, links five principles to Brightwater decisions and draws a four-zone diagram with permitted flows.
Synthetic case. Zones and flows are synthetic; Saltzer and Schroeder (1975) is real.
Errors and limits
One-page diagrams omit detail. Principles may conflict in practice.
Exercises
- EX022 — Why write it down. Why does a small firm benefit from a written architecture? Rubric: 3 = decisions made one at a time contradict each other;; 2 = consistency;; 1 = vague;; 0 = none.
- EX023 — Fail-safe example. How does Brightwater apply fail-safe defaults? Rubric: 3 = new devices join a quarantine network until approved;; 2 = quarantine;; 1 = open network;; 0 = none.
- EX024 — Conveyor flow. What may connect to the conveyor control system? Rubric: 3 = only the vendor's support gateway;; 2 = gateway;; 1 = anything;; 0 = none.
Synthesis
Even small firms need a written architecture grounded in principles and a simple zone diagram.
Continue studying — chapter 08 of 30
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