Polyalphabetic ciphers
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Does a polyalphabetic cipher use a repeating list of shift numbers?
2. Do all letters in the message get shifted by the same amount?
3. Which is harder to break: a polyalphabetic cipher, or a single fixed-shift cipher?
4. Must the same list of shifts be used to decrypt as was used to encrypt?
5. Does using a different list of shifts 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 repeating list of shift numbers | AUsing multiple different shifts | |
| 2Different letters shift by different amounts | BThis isn't polyalphabetic - it's just a single fixed shift | |
| 3A polyalphabetic cipher is harder to break than a single fixed shift | CWhat happens as the shift list repeats | |
| 4Decrypting needs the exact same list of shifts used to encrypt | DMatching the shift list to reverse the cipher | |
| 5Using a different list of shifts to decrypt | EThis won't work - the message stays scrambled | |
| 6Using only one shift number for the whole message | FWhat a polyalphabetic cipher uses instead of one fixed shift |
C
Definitions
Polyalphabetic cipher
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
A polyalphabetic cipher uses a ____
of shift numbers.
2.
The list of shifts _______
across the whole message.
3.
Different letters get shifted by _________
amounts.
4.
This makes the message ______
to break than a single shift.
5.
You need the same list of shifts to _______
it.
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 list of shifts
C
Repeats the list of shifts
Question 2
A
Uses a list of shifts
B
List repeats across message
C
List never repeats
Question 3
A
Different letters shift differently
B
Every letter shifts the same amount
C
The shift list repeats
Question 4
A
Harder to break than one shift
B
Uses a repeating list of shifts
C
Easier to break than one shift
Question 5
A
Same list decrypts it
B
Different list decrypts it
C
Uses a list of shifts
D
List repeats across message
Answer Key
Polyalphabetic ciphers
Section A: Quick Questions
Q1
A — Yes
Q2
B — No
Q3
B — Polyalphabetic cipher
Q4
A — Yes
Q5
A — No
Section B: Match the Pairs
Q1
A repeating list of shift numbers → What a polyalphabetic cipher uses instead of one fixed shift
Q2
Different letters shift by different amounts → What happens as the shift list repeats
Q3
A polyalphabetic cipher is harder to break than a single fixed shift → Using multiple different shifts
Q4
Decrypting needs the exact same list of shifts used to encrypt → Matching the shift list to reverse the cipher
Q5
Using a different list of shifts to decrypt → This won't work - the message stays scrambled
Q6
Using only one shift number for the whole message → This isn't polyalphabetic - it's just a single fixed shift
Section C: Definitions
Q1
Polyalphabetic cipher — A cipher that uses a repeating list of shift numbers, so different letters in a message are shifted by different amounts.Section D: Fill in the Blanks
Q1
A polyalphabetic cipher uses a list
of shift numbers.Q2
The list of shifts repeats
across the whole message.Q3
Different letters get shifted by different
amounts.Q4
This makes the message harder
to break than a single shift.Q5
You need the same list of shifts to decrypt
it.Section E: Spot the Error
Q1
A — Line 1 says it uses one fixed shift, but a polyalphabetic cipher uses a repeating list of different shifts.
Q2
C — Line 3 says the list never repeats, but the list of shifts repeats again and again through the message.
Q3
B — Line 2 says every letter shifts the same amount, but different letters shift by different amounts from the list.
Q4
C — Line 3 says it's easier to break than one shift, but a polyalphabetic cipher is actually harder to break.
Q5
B — Line 2 says a different list can decrypt it, but only the same list of shifts used to encrypt will work.