Obfuscation: Steganography, Masking, Tokenisation and De-identification

Lesson plan

Level

Beginner

Time

About 50 minutes; the steps below add up to 51

Learners explain why a receipt shows four digits, and what invisible ink hides, before the four techniques are named. Predictions then precede a call-centre agent’s view, a shop that holds no card numbers, whether a token can be decrypted, whether deleting names anonymises and how to match needs to techniques; checks follow a known hiding method, test data, stolen tokens, the newspaper’s request and pseudonymised codes. The habit to build: ask what each technique hides, from whom, and whether the original can come back.

Objectives

• Explain steganography and how it differs from encryption
• Describe dynamic and static data masking
• Explain tokenisation and why a token is not ciphertext
• Distinguish de-identification, pseudonymisation and anonymisation
• Choose the right technique for a need

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 encryption lessons first.
• An old till receipt makes the opening concrete.
• The lesson takes about 51 minutes.
• 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 steganography and how it differs from encryption
   • Describe dynamic and static data masking
   • Explain tokenisation and why a token is not ciphertext
   • Distinguish de-identification, pseudonymisation and anonymisation
   • Choose the right technique for a need

   Purpose: Learners explain why a receipt shows four digits, and what invisible ink hides, before the four techniques are named. Predictions then precede a call-centre agent’s view, a shop that holds no card numbers, whether a token can be decrypted, whether deleting names anonymises and how to match needs to techniques; checks follow a known hiding method, test data, stolen tokens, the newspaper’s request and pseudonymised codes. The habit to build: ask what each technique hides, from whom, and whether the original can come back.

2. 1. A shop receipt Think 5 min

   Purpose: Raise partial display and hidden existence from everyday examples.

   Ask

   • Why show four digits?
   • What does invisible ink hide?

   Responses to expect

   • Masking is intuitive; steganography needs the ink.
   • On screen in turns: the opening question, its answer; then the question on invisible ink, and its answer.

   Discussion pause: Ask learners for one more everyday example of each.

   In the lesson window

   • Think it through: Your shop receipt shows your card number with every digit hidden except the last four. Why show those four, and why hide the rest?
   • Think it through: Invisible ink between the lines of an ordinary letter: what does it hide?

3. 2. Four techniques at a glance Explain 3 min

   Purpose: Show the four techniques side by side.

   Ask

   • Which of them is nearest to encryption?

   Responses to expect

   • Tokenisation, by appearance only.
   • On screen in turns: the opening; then four techniques at a glance, with recovery held back; whether the original can be recovered.

   Discussion pause: The recovery column is held back: for each technique, ask whether the original can be got back, and by whom, before revealing it.

4. 3. Steganography Explain 5 min

   Purpose: Explain steganography, its uses and its limit.

   Ask

   • What protects hidden data if the method is known?

   Responses to expect

   • Nothing, unless it was encrypted first.
   • On screen in turns: the opening; then covered writing; encryption and steganography, starting with encryption; steganography; often combined; honest and dishonest uses; the check question on a known method, and its answer; not a substitute for encryption.

   In the lesson window

   • Check your understanding: If the steganography method is known, what protects the hidden data?

5. 4. Data masking Predict 6 min

   Purpose: Explain dynamic and static masking.

   Ask

   • How much should the agent see?
   • Which masking suits testing?

   Responses to expect

   • Learners often think masked data is safe in the database.
   • On screen in turns: the opening; then masking every day; masking and least privilege; the question on a call-centre agent, and its answer; two forms, starting with dynamic masking; static masking; the check question on a test copy, and its answer; dynamic masking still needs a protected database.

   Misconceptions to challenge

   • A learner may believe: “Masked data is protected data.” Respond: Dynamic masking changes only the display.

   In the lesson window

   • Think it through: A call-centre agent needs to confirm which card a customer means. How much of the card number should the agent see?
   • Check your understanding: Developers need realistic data to test a new system. Which form of masking fits?

6. 5. Tokenisation Predict 9 min

   Purpose: Explain tokenisation, the vault and why a token is not ciphertext.

   Ask

   • How could the shop refer to a card it does not hold?
   • What can a thief do with tokens?
   • Can a token be decrypted?

   Responses to expect

   • The difference from encryption is the hard part.
   • Diagram: reveal the encryption row first, then ask how tokenisation differs before revealing its row.
   • On screen in turns: the opening; then the question on a shop without card numbers, and its answer; a payment provider and a shop, starting with the first payment; the repeat order; a stolen database; everything rests on the vault; the check question on stolen tokens, and its answer; tokenisation is not encryption: the question on turning a token back, and its answer; similar from outside, different inside; encryption and tokenisation side by side, starting with encryption; tokenisation; masking, tokenisation, encryption and hashing.

   Misconceptions to challenge

   • A learner may believe: “A token is an encrypted card number.” Respond: There is no key: the token was never computed from the number.

   If the explanation does not land: A cloakroom ticket: it gets your coat back, but tells a thief nothing about the coat.

   In the lesson window

   • Think it through: A shop wants to take repeat payments without ever storing customers’ card numbers. How could it refer to a card it does not hold?
   • Check your understanding: The shop’s database of tokens is stolen. What can the thief do with them?
   • Think it through: Can a token be turned back into the card number with the right key, as ciphertext can?

7. 6. De-identification and anonymisation Predict 10 min

   Purpose: Separate de-identification, pseudonymisation and anonymisation, with the school example.

   Ask

   • Could anyone work out who is who?
   • What did the newspaper need?
   • Are coded data anonymised?

   Responses to expect

   • Removing names is widely taken as anonymising.
   • On screen in turns: the opening; then de-identification; the question on deleted names, and its answer; indirect identification; a school’s attendance data, starting with the request; is that anonymous?; what the newspaper needs; the check question on what the newspaper needed, and its answer; three terms, starting with pseudonymisation; de-identification; anonymisation; de-identified, pseudonymised and anonymised; the check question on codes and a key, and its answer; the legal weight of the distinction; why re-identification keeps succeeding.

   Misconceptions to challenge

   • A learner may believe: “Removing names makes data anonymous.” Respond: Indirect identifiers can still single people out.
   • A learner may believe: “Pseudonymised data is anonymous.” Respond: A kept key links it back; it is still personal data.

   To go further

   • Why do small groups in aggregated figures still risk identifying someone?

   In the lesson window

   • Think it through: A school deletes pupils’ names from an attendance export but keeps date of birth, postcode and year group. Could anyone still work out who is who?
   • Check your understanding: What did the newspaper actually need?
   • Check your understanding: Names are replaced with codes, and the school keeps a key linking the codes to pupils. Is the data anonymised?

8. 7. Choosing between them Predict 3 min

   Purpose: Match each need to a technique.

   Ask

   • Which technique refers without holding, and which keeps and recovers?

   Responses to expect

   • Tokenisation; encryption.
   • On screen in turns: the opening question, its answer; then matching need to technique, starting with hiding a message; seeing part of a value; referring to a value without holding it; keeping a value secret; studying data about people.

   In the lesson window

   • Think it through: Before reading the list: which technique would you use to let a system refer to a value without holding it, and which to keep a value secret but recover it later?

9. 8. Security+ terminology Explain 1 min

   Purpose: Link the lesson to the Security+ wording.

   Ask

   • Which three are listed under obfuscation?

   Responses to expect

   • Steganography, tokenisation and masking.
   • On screen in turns: the opening; then spelling, and what the objectives do not list.

10. 9. 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 photo tests watermarks; masking tests stored data; the survey tests release.
    • On screen in turns: the opening; then the question on a leaked photo, and its answer; the question on dynamic masking, and its answer; the question on sharing survey data, and its answer.

    In the lesson window

    • Apply it: A photo agency wants to trace which client leaked an image. Which technique helps?
    • Apply it: A system uses dynamic masking, so staff see only the last digits. Does the database still need protecting?
    • Apply it: A charity wants to share survey results about its members with researchers. What is the safest starting point?

11. 10. Check your understanding Check 3 min

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

    Ask

    • Answer individually, then compare before revealing.

    Responses to expect

    • The tokenisation questions link to the flow diagram.
    • On screen in turns: the opening; then the revision questions one at a time, each followed by its answer; where to practise next.

12. 11. What to remember Consolidate 2 min

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

    Ask

    • Without looking: what makes a token different from ciphertext?

    Responses to expect

    • It is not derived from the value.
    • On screen in turns: the opening; then the summary; the key terms; the common misunderstandings.

13. 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

    • Hide that it exists.
    • Show only part.
    • Refer without holding.
    • Names gone is not anonymous.
    • Choose by need.

Consolidation

• Hide that it exists.
• Show only part.
• Refer without holding.
• Names gone is not anonymous.
• Choose by need.