Using a cipher wheel or strip

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Your key is a shift of 3. The plaintext is on the inner ring and the ciphertext is on the outer ring. How do you set the wheel?

A Turn the inner ring so inner A lines up with outer D

B Turn the inner ring so inner A lines up with outer C

2. The wheel is set to a shift of 3. You find plaintext B on the inner ring. What ciphertext letter is on the outer ring?

A E

B D

3. Your wheel is set to a shift of 5. Which ciphertext letter lines up with plaintext C?

A G

B H

4. How far do you turn the inner ring to set up ROT13?

A 26 places

B 13 places

5. The wheel is set to ROT13. What does plaintext A become?

A N

B M

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1Key 3: A -> D		AKey 1: CAT -> DBU
2ROT13: A -> N		BA shift of 13 turns A into N and N back into A. Using the wheel twice returns the original message.
3Setting the key: turn the inner ring until A lines up with the letter that matches the shift		CTurn the inner ring so plaintext A lines up with D on the outer ring. Every letter moves 3 places, so HI becomes KL.
4Reading plaintext to ciphertext: find each plaintext letter on the inner ring and read the outer ring letter beside it		DA key of 3 moves A three places to D, not C. C is only a shift of 2, so the inner ring was turned the wrong amount.
5Key 3: A -> C		EKey 5: A lines up with F
6ROT13: A -> M		FROT13 is a shift of 13, so A lines up with N. M is a shift of 12, which is one place short.

Definitions

cipher wheel

Fill in the Blanks

Complete each line of code by filling in the missing parts.

# Turn the inner ring so A meets D key = _

# ROT13 turns the ring half the alphabet key = __

index = 2 key = 3 shifted = (index _ key) % 26

once = rot13("HI") back = _____(once) print(back) # HI

ring = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" key = 13 turned = ring[___:] + ring[:key]

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A SET key TO 3

B SET plain TO 'A'

C SET cipher TO plain - key

D PRINT cipher

Question 2

A # ROT13 on the wheel

B key = 12

C plain = 'A'

D cipher = 'N'

Question 3

A Turn inner ring to key 5

B Plain A lines up with E

C Plain B lines up with G

Question 4

A text = 'HELLO'

B once = rot13(text)

C back = rot12(once)

D print(back)

Question 5

A key = 0

B plain = 'A'

C cipher = 'B'

Answer Key

Using a cipher wheel or strip

Section A: Quick Questions

A — Turn the inner ring so inner A lines up with outer D

A — E

B — H

B — 13 places

A — N

Section B: Match the Pairs

Key 3: A -> D → Turn the inner ring so plaintext A lines up with D on the outer ring. Every letter moves 3 places, so HI becomes KL.

ROT13: A -> N → A shift of 13 turns A into N and N back into A. Using the wheel twice returns the original message.

Setting the key: turn the inner ring until A lines up with the letter that matches the shift → Key 5: A lines up with F

Reading plaintext to ciphertext: find each plaintext letter on the inner ring and read the outer ring letter beside it → Key 1: CAT -> DBU

Key 3: A -> C → A key of 3 moves A three places to D, not C. C is only a shift of 2, so the inner ring was turned the wrong amount.

ROT13: A -> M → ROT13 is a shift of 13, so A lines up with N. M is a shift of 12, which is one place short.

Section C: Definitions

cipher wheel — A tool with two alphabet rings. Turn the inner ring to the key shift so each plaintext letter lines up with its ciphertext letter on the outer ring. ROT13 is a shift of 13.

Section D: Fill in the Blanks

# Turn the inner ring so A meets D
key = 3

# ROT13 turns the ring half the alphabet
key = 13

index = 2
key = 3
shifted = (index + key) % 26

once = rot13("HI")
back = rot13(once)
print(back)  # HI

ring = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
key = 13
turned = ring[key:] + ring[:key]

Section E: Spot the Error

C — To encrypt, you move forward along the ring by the key shift. With a key of 3, A becomes D, so the line should be plain + key.

B — ROT13 is a shift of 13, so the key must be 13. A shift of 12 would turn A into M, not N.

B — With a key shift of 5, A lines up with F (A, B, C, D, E, F is 5 steps). It should say F, which also matches B lining up with G.

C — ROT13 is its own reverse because 13 + 13 = 26. Applying rot13 a second time gets HELLO back, but rot12 would not.

A — A key of 0 means no shift, so A would stay A. To get B the key must be 1.