Choosing symmetric or asymmetric encryption for a scenario
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Two friends who meet daily want to send private messages. They can swap a key in person first. Which type of encryption fits best?
2. A customer types card details into a shop website they have never used before. Which type of encryption fits best?
3. Which answer justifies the choice of encryption properly?
4. Two colleagues who work in the same office want to send each other files. They can agree a key face to face. What should they choose?
5. A customer sends card details to a website. Which key does the customer's browser use to encrypt the data?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1Choose symmetric: two friends who already know each other | AThe two sides are strangers with no safe way to share a secret key, so a public and private key pair is used. | |
| 2Choose asymmetric: customer sending card details to a website | BUse symmetric encryption because both people can already share the key safely. | |
| 3A justified answer for two classmates who already share a secret key | CThe answer has no 'because' justification. It also overlooks that friends who can already share a key safely can use symmetric encryption. | |
| 4A justified answer for a customer paying on a website they have never used before | DUse asymmetric encryption because the customer and website are strangers who cannot share a key safely. | |
| 5Use symmetric for a customer and a website because it is faster. | ESymmetric is the wrong choice for strangers. The customer and website cannot share a secret key safely first, so asymmetric is needed. | |
| 6Use asymmetric encryption for two friends who already share a key. | FBoth people can share one secret key safely in advance, so the same key can encrypt and decrypt quickly. |
C
Definitions
symmetric vs asymmetric
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
IF keyAlreadyShared = TRUE THEN
choice ← "_________"
ENDIF
2.
IF parties = "strangers" THEN
choice ← "__________"
ENDIF
3.
Customer sends card details to a website.
Use asymmetric _______ they are strangers.
4.
Customer sends card details to a website.
Encrypt with the website's ______ key.
5.
Two friends already know each other.
Use symmetric because they can _____ a key.
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
knowEachOther ← TRUE
B
IF knowEachOther = FALSE THEN
C
choice ← "symmetric"
D
ELSE
E
choice ← "asymmetric"
Question 2
A
strangers ← FALSE
B
IF strangers = TRUE THEN
C
choice ← "asymmetric"
D
ENDIF
Question 3
A
scenario ← "card to website"
B
keyShared ← FALSE
C
choice ← "symmetric"
D
OUTPUT choice
Question 4
A
choice ← "symmetric"
B
OUTPUT "Use " + choice
C
OUTPUT "because friends"
D
OUTPUT "cannot share a key"
Question 5
A
choice ← "symmetric"
B
reason ← "they share a key"
C
OUTPUT choice + " although"
D
OUTPUT reason
Answer Key
Choosing symmetric or asymmetric encryption for a scenario
Section A: Quick Questions
Q1
A — Symmetric, because they can already share one key safely
Q2
A — Asymmetric, because the customer and website are strangers with no safe way to share a key
Q3
B — Asymmetric, because the sender never needs to be given a secret key
Q4
A — Symmetric encryption
Q5
B — The website's public key
Section B: Match the Pairs
Q1
Choose symmetric: two friends who already know each other → Both people can share one secret key safely in advance, so the same key can encrypt and decrypt quickly.
Q2
Choose asymmetric: customer sending card details to a website → The two sides are strangers with no safe way to share a secret key, so a public and private key pair is used.
Q3
A justified answer for two classmates who already share a secret key → Use symmetric encryption because both people can already share the key safely.
Q4
A justified answer for a customer paying on a website they have never used before → Use asymmetric encryption because the customer and website are strangers who cannot share a key safely.
Q5
Use symmetric for a customer and a website because it is faster. → Symmetric is the wrong choice for strangers. The customer and website cannot share a secret key safely first, so asymmetric is needed.
Q6
Use asymmetric encryption for two friends who already share a key. → The answer has no 'because' justification. It also overlooks that friends who can already share a key safely can use symmetric encryption.
Section C: Definitions
Q1
symmetric vs asymmetric — Use symmetric if both sides can already share a key safely; use asymmetric for strangers, such as a customer and a website. Justify the choice with 'because'.Section D: Fill in the Blanks
Q1
IF keyAlreadyShared = TRUE THEN
choice ← "symmetric"
ENDIFQ2
IF parties = "strangers" THEN
choice ← "asymmetric"
ENDIFQ3
Customer sends card details to a website.
Use asymmetric because they are strangers.Q4
Customer sends card details to a website.
Encrypt with the website's public key.Q5
Two friends already know each other.
Use symmetric because they can share a key.Section E: Spot the Error
Q1
B — The test is the wrong way round. People who already know each other can share a key safely, so symmetric is chosen when the value is TRUE. It should be IF knowEachOther = TRUE THEN.
Q2
A — A customer and a website are strangers, so strangers should be TRUE. With FALSE the asymmetric choice would never run. It should be strangers ← TRUE.
Q3
C — A customer sending card details to a website has no shared key, so asymmetric encryption is needed. It should be choice ← "asymmetric".
Q4
D — Symmetric encryption is chosen because the two friends already share a key safely. Saying they cannot share a key contradicts the choice. It should be OUTPUT "already share a key".
Q5
C — A justification must use the word 'because' to link the choice to its reason. 'although' does not give a reason. It should be OUTPUT choice + " because".