Chapter 17 — Cryptography concepts
Lesson map
Lesson 17 published. Map, example, EX049.
flowchart TD
N0["Learning outcomes"]
N1["17.1 Encryption"]
N2["17.2 Hashing and pseudonyms"]
N3["17.3 Keys"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4
N4 --> EX["Worked example"]
EX --> Q["Exercise EX049"]
Logical drawing
flowchart LR
N0["Learning outcomes"]
N1["17.1 Encryption"]
N2["17.2 Hashing and pseudonyms"]
N3["17.3 Keys"]
N4["Synthesis"]
N0 --> N1 --> N2 --> N3 --> N4 --> Q["EX049"]
[Learning outcomes]
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v
[17.1 Encryption]
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v
[17.2 Hashing and pseudonyms]
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v
[17.3 Keys]
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v
[Synthesis]
|
v
[Worked example] --> [Exercise EX049]
Learning outcomes
You will (1) explain encryption at rest and in transit; (2) understand hashing and pseudonymisation; (3) manage keys appropriately.
17.1 Encryption
Elena learns the difference between encryption in transit, which protects data moving across networks, and encryption at rest, which protects stored data. Both protect children's records from different threats. She checks that the trust's systems use both and finds that exported reports saved to USB drives are not encrypted. She recommends encrypted USB drives or, better, stopping exports to removable media and using secure sharing instead. Her audit finds that these drives are mostly used for moving reports home to mark.
17.2 Hashing and pseudonyms
Hashing turns data into a fixed-length value that cannot easily be reversed. Elena explains that hashing a pupil identifier alone is weak, because the set of identifiers is small and an attacker can hash them all. A keyed hash with a secret key is stronger. She uses keyed hashes for the reading analysis in Chapter 8. She stresses that pseudonymisation reduces risk but the data remain personal under GDPR Article 4(5). Keys stay with the data protection lead. The key is rotated yearly by the lead.
17.3 Keys
Encryption depends on keys. Elena asks who holds the keys for the trust's backups. The answer is a single IT technician. If he leaves or loses the key, backups become unusable. She recommends storing keys in a managed key service with two authorised custodians and documented recovery. She explains that key management is often the hardest part of cryptography in practice, and that small organisations need simple, well-documented arrangements. The trust keeps a two-page key register. It names holders and locations for each key.
17.4 Limits
Elena notes that encryption does not protect against authorised users misusing data or against data being collected unnecessarily. A teacher with legitimate access can still share a report inappropriately. Encryption is one measure among many. She writes in her notes that cryptography protects confidentiality against outsiders, while access control, training and minimisation address insiders and over-collection. A teacher with legitimate access can still misuse decrypted reports, so encryption alone would not have prevented the misdirected email she studied earlier in the course.
Worked example
Elena stops unencrypted USB exports, uses keyed hashes for pseudonyms, moves backup keys to a managed service with two custodians and states the limits of encryption.
Synthetic case. Systems are synthetic; GDPR Article 4(5) is real.
Errors and limits
Encrypted data are still personal data; encryption reduces risk, not obligations.
Exercises
- EX049 — USB exports. What did Elena recommend for exports on USB drives? Rubric: 3 = encrypted drives or replace with secure sharing;; 2 = one option;; 1 = vague;; 0 = none.
- EX050 — Single key holder. What was the risk of one technician holding backup keys? Rubric: 3 = backups unusable if he leaves or loses the key;; 2 = mentions loss;; 1 = vague;; 0 = none.
- EX051 — Encryption limits. What does encryption not protect against? Rubric: 3 = authorised users misusing data and over-collection;; 2 = one;; 1 = everything;; 0 = none.
Synthesis
Chapter 17 explains cryptography. Chapter 18 introduces research methods.
Continue studying — chapter 17 of 40
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