Vigenere cipher
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Does a Vigenere cipher use a keyword instead of one fixed shift?
2. Do all letters in the message get shifted by the same amount?
3. Does the keyword repeat if it's shorter than the message?
4. Must the same keyword be used to decrypt as was used to encrypt?
5. Does using a different keyword 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 | |
|---|---|---|
| 1A keyword | AMatching the keyword to reverse the cipher | |
| 2Each keyword letter shifts a different message letter | BThis isn't a Vigenere cipher - it's just a single fixed shift | |
| 3A Vigenere cipher is harder to break than a single fixed shift | CUsing a keyword with multiple shifts | |
| 4Decrypting needs the exact same keyword used to encrypt | DWhat happens as the keyword repeats | |
| 5Using a different keyword to decrypt | EThis won't work - the message stays scrambled | |
| 6Using only one shift number for the whole message | FWhat a Vigenere cipher uses instead of one fixed shift |
C
Definitions
Vigenere cipher
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
A Vigenere cipher uses a _______
instead of one shift.
2.
Each keyword letter sets a different _____.
3.
The keyword _______
if it's shorter than the message.
4.
You need the same _______
to decrypt the message.
5.
This makes the message ______
to break than one shift.
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
Uses one fixed shift
B
Uses a keyword instead
C
Keyword sets different shifts
Question 2
A
Keyword sets different shifts
B
Every letter shifts the same
C
Keyword repeats if too short
Question 3
A
Keyword repeats if too short
B
Keyword never repeats
C
Same keyword decrypts it
Question 4
A
Same keyword decrypts it
B
Different keyword decrypts it
C
Keyword sets different shifts
D
Keyword repeats if too short
Question 5
A
Harder to break than one shift
B
Uses a keyword to shift letters
C
Easier to break than one shift
Answer Key
Vigenere cipher
Section A: Quick Questions
Q1
A — Yes
Q2
B — No
Q3
A — Yes
Q4
B — Yes
Q5
A — No
Section B: Match the Pairs
Q1
A keyword → What a Vigenere cipher uses instead of one fixed shift
Q2
Each keyword letter shifts a different message letter → What happens as the keyword repeats
Q3
A Vigenere cipher is harder to break than a single fixed shift → Using a keyword with multiple shifts
Q4
Decrypting needs the exact same keyword used to encrypt → Matching the keyword to reverse the cipher
Q5
Using a different keyword to decrypt → This won't work - the message stays scrambled
Q6
Using only one shift number for the whole message → This isn't a Vigenere cipher - it's just a single fixed shift
Section C: Definitions
Q1
Vigenere cipher — A cipher that uses a keyword, where each keyword letter sets a different shift for the matching letter of the message.Section D: Fill in the Blanks
Q1
A Vigenere cipher uses a keyword
instead of one shift.Q2
Each keyword letter sets a different shift.Q3
The keyword repeats
if it's shorter than the message.Q4
You need the same keyword
to decrypt the message.Q5
This makes the message harder
to break than one shift.Section E: Spot the Error
Q1
A — Line 1 says it uses one fixed shift, but a Vigenere cipher uses a keyword instead of a single shift.
Q2
B — Line 2 says every letter shifts the same, but each keyword letter sets a different shift.
Q3
B — Line 2 says the keyword never repeats, but the keyword repeats if it's shorter than the message.
Q4
B — Line 2 says a different keyword can decrypt it, but only the same keyword used to encrypt will work.
Q5
C — Line 3 says it's easier to break than one shift, but a Vigenere cipher is actually harder to break.