Non-Repudiation

Lesson plan

Level

Beginner

Time

About 60 minutes; the steps below add up to 62

Learners start from a disputed parcel delivery: what evidence would make a denial hard to believe, and what a delivery signature does not show. That gives them the idea of non-repudiation, and its limit, before the term arrives. Predictions then precede each point beginners confuse: a payments system where all three CIA objectives hold yet a key question is open (why a fourth property is needed), a shared login (why identities must be individual), a signed form whose content is intact (integrity against non-repudiation) and a stolen password (what weakens the evidence). The habit to build: ask whether a question is about the state of the data or about who acted.

Objectives

• Explain non-repudiation as evidence of who did what, strong enough that a denial is not credible
• Explain why non-repudiation is not part of the CIA triad
• Name the mechanisms that provide it, and why each depends on individual identities
• Tell an integrity question from a non-repudiation question
• Say what weakens the evidence

Before the lesson

• Open this page on your own screen and use “Open the lesson window” to open the lesson in a second window. Share only that second window.
• Learners need the CIA Triad lesson first.
• Draw two columns on the board, “Has it changed?” and “Who did it?”, to sort questions into during the integrity step.
• The lesson takes about 62 minutes. To teach it in two parts, stop after “Integrity and non-repudiation”; the second part opens with “Four properties at a water-treatment plant”.
• In presentation mode every step is shown in turns: Next reveals one moment, part or answer at a time, and the instructor view names what is on screen and what comes next.

Steps

1. Introduction Opening

   On screen: the lesson’s title, module and number; Next adds its objectives and key terms, as the lesson page lists them; Next again begins the first step.

   Objectives on screen

   • Explain non-repudiation as evidence of who did what, strong enough that a denial is not credible
   • Explain why non-repudiation is not part of the CIA triad
   • Name the mechanisms that provide it, and why each depends on individual identities
   • Tell an integrity question from a non-repudiation question
   • Say what weakens the evidence

   Purpose: Learners start from a disputed parcel delivery: what evidence would make a denial hard to believe, and what a delivery signature does not show. That gives them the idea of non-repudiation, and its limit, before the term arrives. Predictions then precede each point beginners confuse: a payments system where all three CIA objectives hold yet a key question is open (why a fourth property is needed), a shared login (why identities must be individual), a signed form whose content is intact (integrity against non-repudiation) and a stolen password (what weakens the evidence). The habit to build: ask whether a question is about the state of the data or about who acted.

2. 1. “It was not me” Think 6 min

   Purpose: Find the idea of hard-to-deny evidence from a familiar dispute, and its limit: it says who acted, not what state things were in.

   Ask

   • What could the shop show you that would make your denial hard to believe?
   • Does the signature show the laptop was undamaged?

   Responses to expect

   • Signature, time, photograph, tracking. Ask which would be hardest to fake.
   • Some say yes; ask whether anyone looked inside the box.
   • On screen in turns: the opening question, its answer; then the question on what the signature shows, and its answer.

   Discussion pause: Collect the kinds of evidence before revealing the explanation.

   To go further

   • Which of the courier's records would be easiest to fake, and why?

   In the lesson window

   • Think it through: What could the shop show you that would make it hard for you to keep saying the parcel never arrived?
   • Think it through: The courier’s record shows your signature at 10:14 on Tuesday. Does that show the laptop was not opened or damaged on the way?

3. 2. The idea Explain 6 min

   Purpose: Name repudiation and non-repudiation, and fix three points: evidence not prevention, both directions, credible not certain.

   Ask

   • How can the same records protect the engineer who was wrongly blamed?

   Responses to expect

   • Most see it once asked who the records show did make the change.
   • On screen in turns: the opening; then the definition of non-repudiation; the signed-for delivery as the everyday version; three points to fix early, starting with evidence and accountability; that it works in both directions; why the word credibly matters; the check question on the wrongly blamed engineer, and its answer.

   Misconceptions to challenge

   • A learner may believe: “Non-repudiation is about keeping things secret.” Respond: It is about evidence of actions; secrecy is confidentiality.

   If the explanation does not land: Think of a referee’s video replay: it does not stop a foul, but it settles afterwards who committed it, and clears a player who did not.

   In the lesson window

   • Check your understanding: An engineer is told she changed a pump setting overnight. She did not. How can non-repudiation help her?

4. 3. A fourth property outside the triad Predict 6 min

   Purpose: Show why a fourth question is needed, and that non-repudiation sits outside the triad.

   Ask

   • Private, accurate, available, and a wrong payment approved. What is still unknown?

   Responses to expect

   • Some answer with integrity. Remind them the record is accurate by assumption.
   • On screen in turns: the opening question, its answer; then why non-repudiation is not part of the triad; the triad’s three questions; the fourth property, outside the triad; why a fourth question is needed.

   Misconceptions to challenge

   • A learner may believe: “Non-repudiation is the fourth part of the CIA triad.” Respond: A triad has three parts; this is an additional property discussed alongside it.

   Discussion pause: Before the fourth row appears, ask what question the three CIA rows still leave unanswered about the payment.

   In the lesson window

   • Think it through: In a payments system every record is private, accurate and available. Yet a payment has been approved that should not have been. What does the organisation still need to find out?

5. 4. How non-repudiation is provided Predict 8 min

   Purpose: Introduce the four mechanisms, then discover from a shared login that all of them depend on individual identities.

   Ask

   • The shared cabinet login opened it at 03:10. Who did it?

   Responses to expect

   • “The nurse in charge” comes up; ask what the log actually records.
   • On screen in turns: the opening; then the mechanisms, starting with digital signatures; certificates; timestamps; audit records; the question on the shared medicines-cabinet login, and its answer; why each person must act as themselves; what makes evidence hard to deny.

   If the explanation does not land: Return to the parcel: if three people in a house share one name on the delivery record, who signed?

   To go further

   • Why must the log be protected from the person it records, and how might that be done?

   In the lesson window

   • Think it through: Three night-shift nurses share one login to a hospital’s medicines cabinet. The log shows that login opened the cabinet at 03:10. Who opened it?

6. 5. Integrity and non-repudiation Predict 9 min

   Purpose: Separate the two questions, using the consent form and the signed contract.

   Ask

   • Unchanged form, disputed signature: integrity problem or not?
   • Sort these into the two columns: was the price altered; who approved the order; did the file arrive intact; can the sender deny sending it.

   Responses to expect

   • Many call any signature dispute an integrity issue. Ask whether anything in the form changed.
   • The signed-contract example reveals one case at a time: ask the class, before each, which property the case is about.
   • On screen in turns: the opening question, its answer; then the question each property asks; integrity and non-repudiation compared; the signed contract, with its valid signature only; a figure changed on the way; nothing changed, but the supplier denies it; how the two can fail separately; why non-repudiation does not prevent modification.

   Misconceptions to challenge

   • A learner may believe: “Integrity and non-repudiation are the same thing because one signature gives both.” Respond: One mechanism, two questions; either can fail while the other holds.
   • A learner may believe: “Non-repudiation stops data being changed.” Respond: It attributes actions. Detection is integrity; prevention needs other controls.

   In the lesson window

   • Think it through: A parent signs a school-trip consent form online with a digital signature. Later they say they never agreed. The form is exactly as it was signed. Is this an integrity problem?

7. 6. Four properties at a water-treatment plant Experiment 8 min

   Purpose: Apply all four properties to one physical system, before and then with the diagram.

   Ask

   • Name one thing at the plant that each property protects.
   • Why might integrity and availability weigh more heavily here than in an office?

   Responses to expect

   • Confidentiality answers are often about customer data; steer to diagrams, credentials and settings.
   • Diagram: what each property protects is held back; let pairs name something for each property first, then reveal.
   • On screen in turns: the opening question, its answer; then the plant diagram, with what each property protects held back; what each property protects, and what failure looks like; reading the diagram one property at a time; why integrity and availability weigh heavily here.

   Discussion pause: Let pairs fill in all four before showing the diagram.

   In the lesson window

   • Think it through: Before you look at the diagram: for each of the four properties, name one thing at a water-treatment plant that it would protect.

8. 7. Limits of the evidence Predict 6 min

   Purpose: Show what weakens the evidence: shared accounts, stolen credentials, editable or missing records, disagreeing clocks.

   Ask

   • Stolen password, approved payment: can the manager deny it?

   Responses to expect

   • Many say no because the log is clear. Ask whose hands were on the keyboard.
   • On screen in turns: the opening question, its answer; then four things that weaken the evidence; the familiar rules non-repudiation explains.

   Misconceptions to challenge

   • A learner may believe: “A log entry proves who did it.” Respond: Only with individual accounts, sound authentication and a protected log.

   If the explanation does not land: A signed visitors’ book proves little if everyone signs one shared name, if anyone can tear out a page, or if the clock on the wall is wrong.

   In the lesson window

   • Think it through: An attacker steals a manager’s password and approves a payment with it. The audit log shows the manager’s account approved it. Can the manager credibly deny it?

9. 8. Apply it in a new situation Apply 4 min

   Purpose: Set up independent application, ideally on a later day.

   Ask

   • Who will try these now, and who later in the week?

   Responses to expect

   • The editable log tests the fourth evidence condition; the invoice claim tests detection against prevention.
   • On screen in turns: the opening question, its answer; then the question on signed invoices, and its answer.

   In the lesson window

   • Apply it: A company’s IT administrators can edit and delete the log that records their own actions. An administrator is accused of disabling a backup. How strong is the log as evidence?
   • Apply it: A manager says: “We digitally sign our invoices, so nobody can change them.” What is the best response?

10. 9. Check your understanding Check 6 min

    Purpose: Check the lesson against the approved revision-bank questions.

    Ask

    • Answer individually, then compare before revealing.

    Responses to expect

    • The evidence-sources question is multiple-select.
    • On screen in turns: the opening; then the revision questions one at a time, each followed by its answer; where to practise next.

11. 10. What to remember Consolidate 3 min

    Purpose: Summarise the five points, the key terms and the misunderstandings.

    Ask

    • Without looking: what question does non-repudiation ask, and what question does integrity ask?

    Responses to expect

    • Who did it and can they deny it; has the data changed.
    • On screen in turns: the opening; then the summary; the key terms; the common misunderstandings.

12. Lesson recap Closing

    On screen: the lesson’s objectives again; Next adds the closing question, which asks the class to explain each one in their own words without looking back. It says nothing about what anyone has learnt: use the answers to decide what to revisit.

    Points to listen for

    • Hard-to-deny evidence of who did what, which also protects the wrongly accused.
    • Outside the triad: it concerns the trail of actions, not the state of the data.
    • Two questions, one signature: has it changed, and who acted.
    • One identity per person, or the evidence points at a group.
    • Detection and attribution, not prevention; weakened by shared or stolen credentials and editable logs.

Consolidation

• Hard-to-deny evidence of who did what, which also protects the wrongly accused.
• Outside the triad: it concerns the trail of actions, not the state of the data.
• Two questions, one signature: has it changed, and who acted.
• One identity per person, or the evidence points at a group.
• Detection and attribution, not prevention; weakened by shared or stolen credentials and editable logs.