Chapter 17 — Cryptography concepts

Chapter 17 — Cryptography concepts

Lesson map

Lesson 17 published. Map, example, EX049.

flowchart TD
  N0["Learning outcomes"]
  N1["17.1 What cryptography protects"]
  N2["17.2 Policy decisions"]
  N3["17.3 Keys and certificates"]
  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 What cryptography protects"]
  N2["17.2 Policy decisions"]
  N3["17.3 Keys and certificates"]
  N4["Synthesis"]
  N0 --> N1 --> N2 --> N3 --> N4 --> Q["EX049"]

[Learning outcomes]
    |
    v
[17.1 What cryptography protects]
    |
    v
[17.2 Policy decisions]
    |
    v
[17.3 Keys and certificates]
    |
    v
[Synthesis]
    |
    v
[Worked example] --> [Exercise EX049]

Learning outcomes

You will (1) explain what encryption and hashing protect; (2) relate them to policy decisions; (3) manage keys and certificates as governed items.

17.1 What cryptography protects

Sofia learns that encryption keeps data confidential from those without the key, while hashing produces a fingerprint that changes if data change, supporting integrity checks. Digital signatures combine both ideas to show who created something and that it was not altered. At Elmfield, laptop encryption protects lost devices, secure connections protect data in transit and hashes can show that evidence files were not changed after collection. Hashing the backup test evidence later in the course is a direct use of this integrity property.

17.2 Policy decisions

Cryptography requires policy decisions: which data must be encrypted, where and with what approved methods. Sofia drafts a short cryptography standard for Elmfield referencing its data classification: tenant personal data encrypted at rest on devices and in transit; board papers encrypted when shared outside the portal. She learns that ISO/IEC 27002:2022 expects rules on the use of cryptography and on key management, and that simple, clear rules work better than long technical documents nobody reads. A two-line rule for board papers, for instance, is more likely to be followed than a chapter on cipher choices.

17.3 Keys and certificates

Sofia lists Elmfield's certificates and recovery keys. The website certificate renews automatically, but laptop recovery keys are stored only in the device console, which one person administers. If that person left, recovery could fail. She recommends a second administrator and a documented recovery procedure. She learns that most cryptographic failures in small organisations are management failures, such as expired certificates or lost keys, not broken algorithms. A second administrator removes the single point of failure without any change to the encryption itself.

Worked example

Sofia explains encryption and hashing, drafts a short cryptography standard and fixes a single-administrator key risk.

Synthetic case. Elmfield's keys are synthetic; ISO/IEC 27002:2022 is real.

Errors and limits

Encryption does not stop authorised misuse. Key procedures need testing.

Exercises

• EX049 — Hash role. What does hashing support? Rubric: 3 = integrity checks;; 2 = integrity;; 1 = confidentiality;; 0 = none.
• EX050 — Board papers rule. When must board papers be encrypted under the draft standard? Rubric: 3 = when shared outside the portal;; 2 = outside portal;; 1 = never;; 0 = none.
• EX051 — Key risk. What was the risk with laptop recovery keys? Rubric: 3 = one administrator controlled the only store;; 2 = single admin;; 1 = vague;; 0 = none.

Synthesis

Cryptography protects data only when policy and key management are governed well.

Continue studying — chapter 17 of 40

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