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Security in depth · Unit 23 · Lesson 7 of 14
Layers should not share every failure
Find the shared dependency behind three apparently separate protections.
Helpful before thisDefenses and detection
After this lesson you can
- Distinguish product diversity from independence of administrative and recovery authority.
Count what can fail together before counting protective layers.
Independence has a boundary
A common-mode failure defeats several protections through something they share. Two products may have separate software yet depend on the same account, identity provider, electricity, or recovery key. Independence is therefore a claim about a particular failure scenario, not a permanent property of a brand.
Assume a small archive wants production, monitoring, and backups to remain useful when one administrative account is unavailable or misused. The exercise supplies configuration facts only; no misuse has been observed.
Fictional dependency record
- L1: Three vendors provide production hosting, monitoring, and backup storage.
- L2: One administrative group can alter production, disable monitoring, and delete recovery copies in their respective consoles.
- L3: All three consoles require the same identity provider. A separate recovery account exists on paper, but its usable access has not been verified.
Separate two questions
L1 shows product diversity. L2 shows shared authority: separation of storage does not remove the group’s cross-system powers. L3 adds an availability dependency. Making a second administrative group could reduce shared privilege, but would not by itself resolve dependence on the identity provider.
The review should identify which actions need separate authority and which recovery route remains usable during an identity outage. Verification must cover required keys and permissions, not merely the existence of an account name. Extra separation also creates operational work, so assign ownership and a documented recovery process.
Model conclusion: Three products provide different functions, but the supplied record does not establish three independent protection layers for the stated scenario.
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Which conclusion best matches L1-L3?
Show the answer
Correct answer: The products differ, but shared administration and sign-in create common failure paths. The record supports product diversity while identifying authority and availability dependencies that cross all three systems.
Try it
- WriteDraw a three-row dependency table for L1-L3: administrative authority, login dependency, and recovery dependency. Mark a separate product as insufficient evidence of independence.