← VCE Cyber Security

ECDH

A method where two people each combine their own secret with the other's shared piece, ending up with the same matching result without sending the secret.

Part of: VCE Applied Computing - U2O2 - Cyber Security — Module 51, VCE Data Analytics - U4O2 - Cyber Security: Data Security — Module 71, ACARA Digital Technologies Years 9–10 — Cyber Security Threats and Vulnerabilities — Module 140, WA Computer Science ATAR Year 11 — Cyber Security — Module 83

Understanding ECDH in VCE Cyber Security

What it does: Even though each person combines things separately, they both end up with the same result. The secret staying private is what keeps the whole process secure. Only the shared piece is given out, never the secret itself. Each person creates and gives out their own shared piece. Sending the secret defeats the purpose, since it's meant to stay only with its owner.

Common mistakes: Line 1 says to send your secret to them, but the secret must always stay private with its owner. Line 2 says only you get the result, but both people end up with the same matching result.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 51–60) and word search (Modules 41–74).

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Each concept is reinforced from every angle — learned, then applied, then tested.

Learning
Duo
Does each person keep their own secret private?
YesNo
Matches
Sending your secret to the other person
↓
This breaks security - the secret should never be sent
Applying
Meanings
Term
ECDH
Meaning
A method where two people each combine their own secret with the other's shared piece, ending up with the same matching result without sending the secret.
Practice
my_secret = "A1"
Testing
Gaps
Each person keeps their own .
Check Answer
Spots
1Send secret to them
2Keep secret private

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Quick Questions

1. Does each person keep their own secret private?
A. Yes ✓
B. No
Each person's secret stays with them and is never sent anywhere.
2. Is the secret ever sent to the other person?
A. No ✓
B. Yes
Only the shared piece is given out, never the secret itself.
3. Do you combine your own secret with the other person's shared piece?
A. No
B. Yes ✓
This combination is what lets both people reach the same result.
4. Do both people end up with the same matching result?
A. Yes ✓
B. No
Even though each person combines things differently, they both reach the same result.
5. Does each person have their own separate shared piece to give out?
A. No
B. Yes ✓
Each person creates and gives out their own shared piece.

Match the Pairs

Combine your secret with their shared piece → How you reach the matching result
Give out your shared piece → Something that is safe to do openly
Both people reach the same matching result → The outcome of each combining their own secret
The secret must never be sent to anyone → Keeping it private with its owner at all times
Sending your secret to the other person → This breaks security - the secret should never be sent
Combining your secret with your own shared piece → This won't match - you need their shared piece instead

Key Term

ECDH
A method where two people each combine their own secret with the other's shared piece, ending up with the same matching result without sending the secret.

Fill in the Blanks

1. Each person keeps their own secret.
Hint: Type the word for the private value only one person should know.
2. Each person also gives out a shared piece.
Hint: Type the word for the value that gets shared with the other person.
3. You combine your secret with their shared piece.
Hint: Type the word for putting your own secret together with the other person's shared piece.
4. Both people end up with the same matching result.
Hint: Type the word for the final value both people arrive at.
5. The secret itself is never sent to the other person.
Hint: Type the word for what never happens to the secret - it stays with its owner.

Spot the Error

Question 1
A Send secret to them
B Keep secret private
C Share your piece
Line A — Line 1 says to send your secret to them, but the secret must always stay private with its owner.
Question 2
A Keep secret private
B Only you get the result
C Both reach same result
Line B — Line 2 says only you get the result, but both people end up with the same matching result.
Question 3
A Keep secret private
B Share your piece
C Mix secret, own piece
Line C — Line 3 says to mix your secret with your own piece, but you should mix it with their piece instead.
Question 4
A Keep secret private
B Share your piece
C Mix secret, their piece
D Everyone shares one secret
Line D — Line 4 says everyone shares one secret, but each person keeps their own separate secret.
Question 5
A Keep secret private
B Share your piece
C Mix secret, their piece
D Both reach same result
E Secret shared too
Line E — Line 5 says the secret is shared too, but only the piece should ever be shared, never the secret.

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