Chapter 31 — Cryptography and trust services: advanced cases
Lesson map
Lesson 31 published. Map, example, EX091.
flowchart TD
N0["Learning outcomes"]
N1["31.1 Post-quantum migration"]
N2["31.2 End-to-end messaging"]
N3["31.3 Capacity and priorities"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4
N4 --> EX["Worked example"]
EX --> Q["Exercise EX091"]
Logical drawing
flowchart LR
N0["Learning outcomes"]
N1["31.1 Post-quantum migration"]
N2["31.2 End-to-end messaging"]
N3["31.3 Capacity and priorities"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4 --> Q["EX091"]
[Learning outcomes]
|
v
[31.1 Post-quantum migration]
|
v
[31.2 End-to-end messaging]
|
v
[31.3 Capacity and priorities]
|
v
[Synthesis]
|
v
[Worked example] --> [Exercise EX091]
Learning outcomes
You will (1) analyse post-quantum migration for a small organisation; (2) evaluate end-to-end encrypted messaging for patron services; (3) weigh advanced options against capacity.
31.1 Post-quantum migration
Priya studies NIST's post-quantum standards: ML-KEM in FIPS 203 for key establishment, and ML-DSA in FIPS 204 and SLH-DSA in FIPS 205 for signatures. The main near-term risk is "harvest now, decrypt later": recorded traffic could be decrypted once large quantum computers exist. For Tidewell, the most sensitive long-lived data is patron reading history. Priya recommends relying on suppliers and libraries that adopt hybrid key exchange in TLS, keeping inventories ready for migration, and not attempting any custom implementation. She records the recommendation in the inventory plan.
31.2 End-to-end messaging
Tidewell considers letting patrons message librarians about sensitive topics, such as health information requests. Priya evaluates end-to-end encrypted messaging, where only the patron and librarian devices hold keys, so even the consortium's servers cannot read messages. Benefits include strong privacy; costs include losing messages if a device is lost, difficulty with shared librarian inboxes and inability to scan for abuse. She recommends a reputable existing service with published security design rather than building one. Grace takes the recommendation to the outreach team.
31.3 Capacity and priorities
Priya weighs these advanced options against Tidewell's capacity: a small IT team, limited budget and many basic gaps still open. She recommends finishing basic controls first, such as inventory, automated renewal and backup encryption, then adopting post-quantum protections through supplier updates as they arrive. Advanced cryptography adds value only when foundations are in place, and complexity beyond the team's ability to operate it becomes a risk itself. Grace agrees and adds the advanced options to a three-year roadmap, to be revisited once the basic controls are complete and measured.
Worked example
Priya recommends post-quantum readiness through suppliers and inventories, an existing end-to-end messaging service for sensitive patron requests, and finishing basic controls first.
Synthetic case. Tidewell's options are invented; FIPS 203, 204 and 205 are real.
Errors and limits
Post-quantum migration timelines are uncertain; avoid panic and complacency. End-to-end encryption shifts risk to device and key loss.
Exercises
- EX091 — Harvest now. What does "harvest now, decrypt later" mean? Rubric: 3 = recorded traffic decrypted later when large quantum computers exist;; 2 = future decryption;; 1 = vague;; 0 = none.
- EX092 — E2E cost. Name two costs of end-to-end encrypted patron messaging. Rubric: 3 = two of message loss with devices, shared inbox difficulty, no abuse scanning;; 2 = one;; 1 = vague;; 0 = none.
- EX093 — Priority advice. What did Priya advise before adopting advanced options? Rubric: 3 = finish basic controls first (inventory, renewal, backup encryption);; 2 = basics;; 1 = rush;; 0 = none.
Synthesis
Advanced cryptography should follow solid foundations and arrive through vetted suppliers matched to the organisation's capacity.
Continue studying — chapter 31 of 40
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