← VCE Cyber Security

RSA

A way of locking and unlocking messages using two matching keys: a public key anyone can have, and a private key kept secret by its owner.

Part of: VCE Applied Computing - U2O2 - Cyber Security — Module 50, VCE Data Analytics - U4O2 - Cyber Security: Data Security — Module 70, ACARA Digital Technologies Years 9–10 — Cyber Security Threats and Vulnerabilities — Module 141, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 33, WA Computer Science ATAR Year 11 — Cyber Security — Module 82

Understanding RSA in VCE Cyber Security

What it does: Since the public key is safe to share, it can be given out openly to anyone. The private key must stay secret so only its owner can use it. Others use your public key to lock a message that only you can unlock. Each person needs their own private key so only they can unlock their own messages. Locking a message for someone is done using their public key. Unlocking a message can only be done with the matching private key.

Common mistakes: Line 1 says the public key should be kept secret, but the public key is meant to be shared openly. Line 2 says the private key should be shared, but the private key must always stay secret.

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 41–50) and word search (Modules 41–74).

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

Learning
Duo
Should the public key be shared with everyone?
YesNo
Matches
Sharing your private key with a friend
↓
This breaks security - only the owner should have it
Applying
Meanings
Term
RSA
Meaning
A way of locking and unlocking messages using two matching keys: a public key anyone can have, and a private key kept secret by its owner.
Practice
pub_key = "shared"
Testing
Gaps
The key can be shared with anyone.
Check Answer
Spots
1Public key: keep it secret
2Private key: keep it secret

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Quick Questions

1. Should the public key be shared with everyone?
A. Yes ✓
B. No
The public key is meant to be given out openly.
2. Should the private key be shared with everyone?
A. No ✓
B. Yes
The private key must stay secret so only its owner can use it.
3. Which key locks a message meant for you: your public key, or your private key?
A. Your private key
B. Your public key ✓
Others use your public key to lock a message that only you can unlock.
4. Which key unlocks that message: your public key, or your private key?
A. Your public key
B. Your private key ✓
Only your private key can unlock a message locked with your public key.
5. Is it safe to give your private key to someone else?
A. No ✓
B. Yes
Sharing your private key lets anyone unlock messages meant only for you.

Match the Pairs

Lock a message → Uses the public key
Unlock a message → Uses the matching private key
The public key can be shared with anyone → Give it out openly
The private key must stay secret → Never give it to anyone else
Sharing your private key with a friend → This breaks security - only the owner should have it
Using someone else's public key to unlock their message → This won't work - only their private key can unlock it

Key Term

RSA
A way of locking and unlocking messages using two matching keys: a public key anyone can have, and a private key kept secret by its owner.

Fill in the Blanks

1. The public key can be shared with anyone.
Hint: Type the word for the key that anyone is allowed to have.
2. The private key must always stay secret.
Hint: Type the word for the key that only its owner should ever have.
3. You lock a message using the public key.
Hint: Type the word for what you do to a message using someone's public key.
4. You need the private key to unlock a message.
Hint: Type the word for what the private key does to a locked message.
5. Public and private keys form a matching pair.
Hint: Type the word that describes how the two keys are connected together.

Spot the Error

Question 1
A Public key: keep it secret
B Private key: keep it secret
C Both keys: always linked
Line A — Line 1 says the public key should be kept secret, but the public key is meant to be shared openly.
Question 2
A Public key: share it openly
B Private key: share it openly
C Both keys: a matching pair
Line B — Line 2 says the private key should be shared, but the private key must always stay secret.
Question 3
A You lock with public key
B You unlock with private key
C You unlock with public key
Line C — Line 3 says you unlock a message with the public key, but only the matching private key can unlock it.
Question 4
A Public key: share openly
B Private key: keep secret
C Each person: own private key
D Two people: same private key
Line D — Line 4 says two people can share one private key, but each person's private key must stay their own.
Question 5
A Keep private key to yourself
B Public key: share with anyone
C Both keys always come in pairs
D Give your private key away
Line D — Line 4 says to give away your private key, but the private key must always stay secret with its owner.

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