Encryption and decryption
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Is plaintext the original, readable message?
2. Is ciphertext the scrambled, unreadable message?
3. Which turns plaintext into ciphertext: encryption, or decryption?
4. Which turns ciphertext back into plaintext: encryption, or decryption?
5. Is a key needed to encrypt and decrypt a message?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1Plaintext | AThis doesn't work - plaintext can be read by anyone | |
| 2Ciphertext | BUnscrambling a message with a key | |
| 3Encryption turns plaintext into ciphertext | CThe original, readable message | |
| 4Decryption turns ciphertext back into plaintext | DScrambling a message with a key | |
| 5Sending plaintext to keep a message private | EThe scrambled, unreadable message | |
| 6Decrypting a message with the wrong key | FThis won't work - only the correct key can decrypt it |
C
Definitions
Encryption
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
The original readable message is called
_________.
2.
The scrambled, unreadable message is called
__________.
3.
You need a ___
to encrypt and decrypt a message.
4.
__________ turns plaintext into ciphertext.
5.
__________
turns ciphertext back into plaintext.
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
Ciphertext is readable
B
Plaintext is readable
C
Ciphertext is scrambled
Question 2
A
Plaintext is readable
B
Plaintext is scrambled
C
Ciphertext is scrambled
Question 3
A
Encryption scrambles text
B
Decryption unscrambles text
C
Encryption unscrambles text
Question 4
A
A key is needed to encrypt
B
A key is needed to decrypt
C
Encryption scrambles text
D
No key is needed to decrypt
Question 5
A
Decryption scrambles text
B
Decryption unscrambles text
C
Encryption scrambles text
Answer Key
Encryption and decryption
Section A: Quick Questions
Q1
B — Yes
Q2
B — Yes
Q3
A — Encryption
Q4
A — Decryption
Q5
A — Yes
Section B: Match the Pairs
Q1
Plaintext → The original, readable message
Q2
Ciphertext → The scrambled, unreadable message
Q3
Encryption turns plaintext into ciphertext → Scrambling a message with a key
Q4
Decryption turns ciphertext back into plaintext → Unscrambling a message with a key
Q5
Sending plaintext to keep a message private → This doesn't work - plaintext can be read by anyone
Q6
Decrypting a message with the wrong key → This won't work - only the correct key can decrypt it
Section C: Definitions
Q1
Encryption — Turning a readable message into a scrambled, unreadable message using a key, so it can only be read again with decryption.Section D: Fill in the Blanks
Q1
The original readable message is called
plaintext.Q2
The scrambled, unreadable message is called
ciphertext.Q3
You need a key
to encrypt and decrypt a message.Q4
Encryption turns plaintext into ciphertext.Q5
Decryption
turns ciphertext back into plaintext.Section E: Spot the Error
Q1
A — Line 1 wrongly says ciphertext is readable, but ciphertext is scrambled and unreadable without the key.
Q2
B — Line 2 wrongly says plaintext is scrambled, but plaintext is the original readable message.
Q3
C — Line 3 wrongly says encryption unscrambles text, but encryption is what scrambles it - decryption unscrambles.
Q4
D — Line 4 wrongly says no key is needed to decrypt, but a key is required to decrypt correctly.
Q5
A — Line 1 wrongly says decryption scrambles text, but decryption is what unscrambles ciphertext back to plaintext.