Chapter 50 — Final defense
Lesson map
Lesson 50 published. Map, example, EX099.
flowchart TD
N0["Learning outcomes"]
N1["50.1 Presentation"]
N2["50.2 Likely questions"]
N3["50.3 Demonstration"]
N4["50.4 Forward plan"]
N5["Engineering note"]
N6["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4 --> N5 --> N6
N6 --> EX["Worked example"]
EX --> Q["Exercise EX099"]
Logical drawing
flowchart LR
N0["Learning outcomes"]
N1["50.1 Presentation"]
N2["50.2 Likely questions"]
N3["50.3 Demonstration"]
N4["50.4 Forward plan"]
N5["Engineering note"]
N6["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4 --> N5 --> N6 --> Q["EX099"]
[Learning outcomes]
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[50.1 Presentation]
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[50.2 Likely questions]
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[50.3 Demonstration]
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[50.4 Forward plan]
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[Engineering note]
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[Synthesis]
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[Worked example] --> [Exercise EX099]
Learning outcomes
You will (1) present and defend the engineering thesis; (2) answer technical, ethical and management questions; (3) demonstrate the system or its evidence; and (4) set a forward plan for the system's next cryptographic change. It completes the course.
50.1 Presentation
Twenty minutes: problem and stakes; requirements; architecture and key decisions; results with evidence; failures and recovery; residual risk; what you would do differently. Use diagrams with text alternatives.
Twenty minutes is short, so each part gets roughly three minutes, with results and residual risk given the most care. The final question, what you would do differently, shows reflection and often draws the panel's most useful follow-up. Text alternatives for diagrams help panel members using screen readers and force the presenter to state each diagram's point in words.
50.2 Likely questions
- Why hybrid rather than pure PQC? (Hedge against cryptanalytic surprise; cite Rainbow/SIKE; cost accepted.)
- Why are portal certificates still classical? (Active quantum attacks need a CRQC at connection time; ecosystem support and size; plan and trigger for change.)
- How do you know fallback is not a downgrade path? (Transcript authentication; logged, dated fallback; lab downgrade test.)
- What happens if ML-KEM is broken? (X25519 still protects against classical attackers; agility path to an alternative such as HQC once standardized; measured time-to-replace.)
- What would you do with twice the budget? (Prioritize by exposure ÷ effort.)
50.3 Demonstration
Show the dashboard, a policy-driven algorithm change in the replica environment and the dossier tracing for one claim.
Each part of the demonstration supports a different claim: the dashboard shows measurement in operation, the policy change shows agility, and the dossier trace shows that results are backed by evidence. Running it in the replica environment avoids any risk to BPA's services. The presenter rehearses each step with a timer and has screenshots ready in case the environment fails during the defence.
50.4 Forward plan
Agility is the legacy: schedule re-verification of standards (FN-DSA, HQC, revised IR 8547), annual algorithm-break tabletops, CBOM refresh automation and partner reviews.
Each item has an owner and a date, so the plan survives the end of the programme. Re-verifying standards catches changes such as a final FN-DSA standard or HQC's publication, which would add options for BPA. Annual tabletops keep the time-to-replace figure current, while partner reviews track the remaining classical paths toward their sunset dates and flag any slipping.
50.5 Common errors and limits
- Claiming the organization is "quantum-safe".
- No answer for algorithm compromise.
- Demonstrations that depend on production systems.
Claiming "quantum-safe" invites the panel to list the classical certificates and unknown assets that remain. Without an answer for algorithm compromise, the agility work has no visible purpose. A demonstration that needs production systems risks an outage during the defence and cannot be repeated by reviewers afterwards; the replica environment avoids both problems. Candidates who prepare honest answers on these points usually find the panel's questions easier.
Engineering note
After the defense, hand the system to its owners with a short letter that states what was achieved, what remains, the dates of upcoming expiries and reviews, and how to reach the people who know the design. Quantum readiness depends on continuity more than on any single engineer, so the final act of the course is to make sure the capability survives the end of the project and the next algorithm change finds a prepared team.
Exercises
- EX099 — Defense answers. Write answers to the five questions in 50.2 for your own capstone. Rubric: 3 = evidence-based, bounded.
- EX100 — Forward plan. Write the two-year forward plan for BPA's cryptography after the capstone. Rubric: 3 = re-verification, tabletops, inventory, partner milestones.
Synthesis
The defense shows a validated, measured and agile migration, answers hard questions with evidence and leaves a plan for the next change — because quantum readiness is a capability, not a finish line.
Continue studying — chapter 50 of 50
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