Chapter 5 — Security literacy | Technologist Quantum and post-quantum security

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Chapter 5 — Security literacy

Lesson map

Lesson 05 published. Map, example, EX009.

flowchart TD
  N0["Learning outcomes"]
  N1["5.1 Properties and changes"]
  N2["5.2 Risk vocabulary"]
  N3["5.3 Two patterns"]
  N4["5.5 Practical activity"]
  N5["5.7 Turning risk into tasks"]
  N6["Synthesis"]
  N0 --> N1 --> N2 --> N3 --> N4 --> N5 --> N6
  N6 --> EX["Worked example"]
  EX --> Q["Exercise EX009"]

Logical drawing

flowchart LR
  N0["Learning outcomes"]
  N1["5.1 Properties and changes"]
  N2["5.2 Risk vocabulary"]
  N3["5.3 Two patterns"]
  N4["5.5 Practical activity"]
  N5["5.7 Turning risk into tasks"]
  N6["Synthesis"]
  N0 --> N1 --> N2 --> N3 --> N4 --> N5 --> N6 --> Q["EX009"]

[Learning outcomes]
    |
    v
[5.1 Properties and changes]
    |
    v
[5.2 Risk vocabulary]
    |
    v
[5.3 Two patterns]
    |
    v
[5.5 Practical activity]
    |
    v
[5.7 Turning risk into tasks]
    |
    v
[Synthesis]
    |
    v
[Worked example] --> [Exercise EX009]

Learning outcomes

You will (1) apply confidentiality, integrity, availability and authenticity to service changes; (2) relate assets, threats, vulnerabilities and controls; (3) explain harvest-now-decrypt-later and forge-later; and (4) recognise availability risk in cryptographic change.

5.1 Properties and changes

Implementers change cryptography to improve confidentiality and authenticity, but every change risks availability. A hybrid group that a load balancer cannot parse is an outage. Good practice treats availability as a co-equal requirement: staged rollout, rollback, monitoring.

The rule shows in KLS's own records: the monitoring probe that timed out on the staging gateway would have been a production alert storm if the group had gone live everywhere at once. Each hybrid change therefore carries a rollback, a dashboard and a canary stage in its plan.

5.2 Risk vocabulary

An asset (shipment records), a threat (an adversary recording traffic), a vulnerability (classical key exchange) and a control (hybrid key exchange) combine into a risk scenario. Quantum vulnerabilities are properties of algorithms, not bugs, and become exploitable when a capability appears.

Writing the four parts separately also shows where a control acts. Hybrid key exchange removes the vulnerability for future sessions only; it does nothing for traffic already recorded. Shortening retention reduces the asset's value instead. For KLS's partner SFTP the full scenario reads: customs documents, recorded by an adversary on a transit network, readable because of ECDH key exchange, mitigated by mlkem768x25519-sha256 from the upgrade date onward.

5.3 Two patterns

Harvest now, decrypt later: recorded traffic is decrypted once a quantum computer exists; urgent for data whose confidentiality lasts beyond that time. Forge later: once a quantum computer exists, signatures can be forged; urgent for long-lived trust (root CAs, firmware signing, documents verified for years) and for devices that cannot be updated.

The urgency of each is a matter of dates. HNDL exposure starts the day traffic is recorded, so for KLS's ten-year shipment data every classical session today matters. Forge-later exposure starts only when forgery becomes possible and lasts while the key is trusted, so the 15-year internal root is urgent and a weekly JWT key is not.

5.4 Worked example

KLS's partner SFTP service carries customs documents kept confidential ten years; it uses ECDH key exchange: HNDL-exposed now. Its host key is Ed25519: forge-later exposure, lower urgency because host keys can be rotated quickly once SSH clients support post-quantum host-key algorithms. The API's JWT signing keys rotate weekly: forge-later exposure is minimal until a quantum computer exists.

The three cases give KLS three different responses. The SFTP key exchange is scheduled for the next maintenance window. The host key is recorded as residual risk with a trigger: when OpenSSH ships a post-quantum host-key algorithm KLS clients support, rotate. The JWT keys need nothing beyond keeping rotation automated.

5.5 Practical activity

Write three risk scenarios for KLS services using the asset–threat–vulnerability–control pattern; label each HNDL, forge-later or neither.

A complete scenario names all four parts and the label. Example: asset, billing database replication carrying seven-year invoices; threat, recording on the provider's inter-zone network; vulnerability, ECDHE-P256 in the replication TLS; control, provider-supported hybrid or application-layer field encryption; label HNDL. Include one scenario labelled neither, such as AES-256 backups, and explain why: Grover's speed-up leaves a 256-bit key with ample margin, so no quantum-driven action is needed.

5.6 Common errors and limits

Forgetting availability in change plans.
Treating all quantum risk as equally urgent.
Calling algorithms "bugs".

Each error leads to a recognisable failure. A plan without availability work enables hybrid on the portal and discovers the old proxy at a customer site through a support call. Treating all exposure as urgent puts weekly JWT keys in the same queue as ten-year SFTP traffic and slows both. Calling RSA a "bug" invites a patch mindset; there is no patch, only replacement, and the timeline depends on a capability that does not yet exist.

5.7 Turning risk into tasks

Implementers translate each risk scenario into work items with a clear definition of done. "Partner SFTP HNDL exposure" becomes: confirm the OpenSSH version on the SFTP hosts supports mlkem768x25519-sha256; enable it first in the server's key-exchange list in staging; check which partner clients negotiate it; publish a partner notice; promote to production; monitor the share of sessions using it. Each item has an owner and evidence that proves it is complete. Risk statements that never become tasks are the most common way security work stalls between the risk register and the platform backlog.

Keep availability in every definition of done: a task is not complete until rollback has been tested and monitoring shows no rise in failures.

Exercises

EX009 — Classify. Label HNDL, forge-later or neither: office VPN traffic, CI code-signing key, AES-256 backups, TLS to the customer portal. Rubric: 3 = four correct with reasons.
EX010 — Availability. Name two ways enabling hybrid key exchange could cause an outage and one control for each. Rubric: 3 = two failure modes with controls.

Synthesis

Implementers must weigh confidentiality and authenticity gains against availability risk, and distinguish the time-shaped patterns of harvest-now-decrypt-later and forge-later.

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