Students use a data-flow diagram of the club app to name a risk and a defence at each point where data travels, is stored or is changed, then threat-model two new features (AC9TDI10P13 node 1). Defensive and conceptual. A 5E mission lesson.
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Students will be able to
I can follow data through a system on a data-flow diagram.
I can name what could go wrong where data travels, is stored or is changed.
I can match a defence to each point.
Timing
Engage and Explore 12 min · Explain 8 min · Elaborate 18 min · Evaluate 7 min
Before class
Try the board yourself. The club app is made up.
The one idea: follow the data; each point (travelling, stored, who may act) has its own risk and its own defence.
Typical width: have students draw the data-flow diagram for an app they know (the school canteen, a game) on paper first, then mark the points.
Running the lesson
Engage: ask what the padlock actually means.
Explore: ask which point they defended wrongly first, and why.
Explain: model the three questions on the admin page.
Elaborate: ask what the photos feature added to the diagram.
Evaluate: compare answers for the canteen app.
The hard part (on purpose)
Students pick HTTPS for everything. Ask: is this data travelling right now, or sitting in the database?
When students get stuck
What you will see
A question to ask
The fix
A student thinks HTTPS covers everything (Sam's mistake).
Where is the data at this point: on the network, or in the database?
Each place needs its own defence.
A student confuses hashing with HTTPS.
Is the password moving or stored?
HTTPS on the way, hashing in storage.
Answers to the checks
Engage: is the padlock enough?: The club app uses HTTPS (the padlock). Which data does that protect? Only data on the way. Stored passwords and who may use the admin page need their own defences.
Explore: defend each point: For each point in the diagram, choose what could go wrong and the defence that fits.
Sign-in: read on the way, HTTPS. Stored passwords: copied from storage, hash them. Admin page: used by the wrong person, access control and MFA.
Explain: follow the data: Sam secures the club app. Click the line where it first goes wrong. line 4 Line 4: HTTPS only protects data while it travels. The stored passwords and the admin page are still open.
Elaborate: photos: Members can now upload photos. Defend all five points.
The upload travels (HTTPS); who can see each photo is about the wrong person (access control). New features add new points.
Elaborate: messages: The committee wants members to message each other. Threat-model the new feature.
Sending: HTTPS. Saved messages: encrypt them. Opening a conversation: only the people in it (access control).
The canteen app: The school's canteen app lets parents top up lunch money. Which point needs access control most? Changing whose account the money goes to Pages that change data, or money, are where the wrong person does harm.
Solutions
One possible solution for each task. Other correct programs are fine.
Elaborate: photos
Open task: any program that does what the step asks.
Elaborate: messages
Open task: any program that does what the step asks.
Stretch and support
Stretch: Draw the diagram for the canteen app with three actors (parent, school, bank) and defend every arrow.
Support: A card with the three questions: travelling? stored? who may act?
Exit ticket
Name two points in a web app where data is at risk, and the defence for each.
Travelling between browser and server (HTTPS); stored passwords (salted hashes); the admin page (access control and MFA).
What each step is for
Engage: is the padlock enough?: Committing to whether HTTPS secures the whole app tests the new move: each point in a data flow needs its own defence.
Explore: defend each point: Students match a risk and a defence to each point of the diagram and find that one defence doesn't fit all.
Explain: follow the data: The teacher models the threat-model questions on one point. Sam trusts HTTPS for everything, the misconception planted after the method.
Elaborate: photos: One change: a new feature adds two points to the diagram, one travelling and one about who may see.
Elaborate: messages: Applying the model to a feature on their own: students place each point and its defence without the earlier diagram.