Caesar cipher
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Does a Caesar cipher shift each letter by a fixed number?
2. Which direction encrypts a message: shifting forward, or shifting backward?
3. Which direction decrypts a message: shifting forward, or shifting backward?
4. Must the shift used to decrypt match the shift used to encrypt?
5. Does using a different shift than the one used to encrypt still decrypt the message correctly?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1Shift forward | AReversing the shift correctly | |
| 2Shift backward | BHow you decrypt with a Caesar cipher | |
| 3The shift number decides how far each letter moves | CThe key of a Caesar cipher | |
| 4The same shift must be used to decrypt as was used to encrypt | DThis won't work - the message stays scrambled | |
| 5Decrypting with a different shift than was used to encrypt | EHow you encrypt with a Caesar cipher | |
| 6Using no shift at all | FThis isn't encryption - the message stays unchanged |
C
Definitions
Caesar cipher
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
The _____ is how many places a letter moves.
2.
To _______, shift each letter forward.
3.
To _______, shift each letter backward.
4.
You must use the ____ shift to decrypt.
5.
Each ______ shifts by the same amount.
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
Backward shift encrypts
B
Forward shift encrypts it
C
Backward shift decrypts it
Question 2
A
Forward shift encrypts it
B
Forward shift decrypts it
C
Backward shift decrypts it
Question 3
A
Same shift decrypts it
B
Same shift encrypted it
C
Different shift decrypts it
Question 4
A
Shift is the key
B
Forward shift encrypts
C
Backward shift decrypts
D
No shift also encrypts
Question 5
A
Shift is a fixed number
B
Forward shift encrypts
C
Backward shift decrypts
D
Same shift must be used
E
Any shift can decrypt it
Answer Key
Caesar cipher
Section A: Quick Questions
Q1
A — Yes
Q2
B — Forward
Q3
A — Backward
Q4
B — Yes
Q5
A — No
Section B: Match the Pairs
Q1
Shift forward → How you encrypt with a Caesar cipher
Q2
Shift backward → How you decrypt with a Caesar cipher
Q3
The shift number decides how far each letter moves → The key of a Caesar cipher
Q4
The same shift must be used to decrypt as was used to encrypt → Reversing the shift correctly
Q5
Decrypting with a different shift than was used to encrypt → This won't work - the message stays scrambled
Q6
Using no shift at all → This isn't encryption - the message stays unchanged
Section C: Definitions
Q1
Caesar cipher — A cipher that encrypts a message by shifting each letter forward by a fixed number, and decrypts it by shifting each letter back by the same number.Section D: Fill in the Blanks
Q1
The shift is how many places a letter moves.Q2
To encrypt, shift each letter forward.Q3
To decrypt, shift each letter backward.Q4
You must use the same shift to decrypt.Q5
Each letter shifts by the same amount.Section E: Spot the Error
Q1
A — Line 1 says backward shift encrypts, but shifting forward is what encrypts a message.
Q2
B — Line 2 says forward shift decrypts, but shifting backward is what decrypts a message.
Q3
C — Line 3 says a different shift can decrypt it, but only the same shift used to encrypt will work.
Q4
D — Line 4 says no shift also encrypts, but a message needs an actual shift number to be encrypted.
Q5
E — Line 5 says any shift can decrypt it, but only the matching shift used to encrypt works correctly.