Chapter 11 — Operating systems

Lesson map

Lesson 11 published. Map, example, EX031.

flowchart TD
  N0["Learning outcomes"]
  N1["11.1 Accounts and permissions"]
  N2["11.2 Update prompts"]
  N3["11.3 Reducing burden"]
  N4["Synthesis"]
  N0 --> N1 --> N2 --> N3 --> N4
  N4 --> EX["Worked example"]
  EX --> Q["Exercise EX031"]

Logical drawing

flowchart LR
  N0["Learning outcomes"]
  N1["11.1 Accounts and permissions"]
  N2["11.2 Update prompts"]
  N3["11.3 Reducing burden"]
  N4["Synthesis"]
  N0 --> N1 --> N2 --> N3 --> N4 --> Q["EX031"]

[Learning outcomes]
    |
    v
[11.1 Accounts and permissions]
    |
    v
[11.2 Update prompts]
    |
    v
[11.3 Reducing burden]
    |
    v
[Synthesis]
    |
    v
[Worked example] --> [Exercise EX031]

Learning outcomes

You will (1) explain accounts, permissions and updates in an operating system; (2) describe how update prompts affect users; (3) propose settings that reduce user burden.

11.1 Accounts and permissions

An operating system manages accounts and controls what each account can do. At Ashcombe, counter computers use shared accounts, which makes it impossible to tell who did what. Office laptops give staff administrator rights so they can install printer drivers, which also lets malware install itself. Nadia learns that separating ordinary and administrator accounts limits damage from mistakes and attacks. She recommends named accounts with tap-card login at counters and removing routine administrator rights, with IT installing drivers centrally instead of relying on each person.

11.2 Update prompts

Operating systems ask users to restart for updates. Staff at Ashcombe postpone restarts because they come at busy times and take several minutes. Nadia counts that some laptops have postponed updates for over a month, leaving known weaknesses unpatched. She connects this to the compliance budget idea of Beautement, Sasse and Wonham (2008): people have limited willingness to spend effort on security, and when prompts arrive at bad times they are postponed. Blaming staff for postponing would ignore the timing problem built into the system.

11.3 Reducing burden

Nadia proposes that updates install automatically overnight when libraries are closed, with laptops left on charge in offices. Restarts during opening hours become rare. She also suggests that IT monitor update status centrally, so that no one has to remember. The change moves effort from individuals to the system, which is more reliable. Dr Prescott notes that this is a recurring theme in human factors: when a secure behaviour depends on many people remembering, design the system to do it for them where possible.

Worked example

Nadia recommends named accounts and removing routine admin rights, links postponed updates to the compliance budget and proposes overnight updates.

Synthetic case. Settings are synthetic; Beautement et al. (2008) is real.

Errors and limits

Overnight updates fail if devices are off. Removing admin rights increases IT workload.

Exercises

• EX031 — Shared account problem. What is the problem with shared counter accounts?
  Show marking criteria

  Rubric: 3 = nobody can tell who did what;; 2 = accountability;; 1 = vague;; 0 = none.
• EX032 — Compliance budget. What does the compliance budget describe?
  Show marking criteria

  Rubric: 3 = limited willingness to spend effort on security;; 2 = effort;; 1 = vague;; 0 = none.
• EX033 — Burden shift. Where does Nadia move the update effort?
  Show marking criteria

  Rubric: 3 = from individuals to the system;; 2 = system;; 1 = users;; 0 = none.

Synthesis

Operating system settings can shift security effort from people to systems.

Continue studying — chapter 11 of 40

← Chapter 10 (draft) · Course chapter index · Chapter 12 (draft) →