Cryptography: Caesar and Vigenere Ciphers Worksheet

Question 1

Use a Caesar cipher with a shift of 3 to encrypt the word MATH.

Accepted Answer

The encrypted word is PDWK because M shifts to P, A shifts to D, T shifts to W, and H shifts to K.

Question 2

Use a Caesar cipher with a shift of 3 to decrypt the message KHOOR.

Accepted Answer

The decrypted message is HELLO because each letter is shifted 3 places backward in the alphabet.

Question 3

Use a Caesar cipher with a shift of 5 to encrypt the word CODE.

Accepted Answer

The encrypted word is HTIJ because C shifts to H, O shifts to T, D shifts to I, and E shifts to J.

Question 4

Use a Caesar cipher with a shift of 3 to decrypt the message FUBSWR.

Accepted Answer

The decrypted message is CRYPTO because F shifts back to C, U shifts back to R, B shifts back to Y, S shifts back to P, W shifts back to T, and R shifts back to O.

Question 5

A Caesar cipher message is BQQMF. Test possible shifts and decide which shift makes a common English word. What is the plaintext and the shift?

Accepted Answer

The plaintext is APPLE, and the shift is 1 because each encrypted letter moves one place backward to make a readable word.

Question 6

In a Caesar cipher, the most common plaintext letter E was encrypted as J. What shift was used, and what is the plaintext of YJXY?

Accepted Answer

The shift was 5 because E moved forward to J. The plaintext of YJXY is TEST because each letter is shifted 5 places backward.

Question 7

Use a Vigenere cipher to encrypt DOG with the key CAT. Use A = 0, so C means shift 2, A means shift 0, and T means shift 19.

Accepted Answer

The encrypted message is FOZ because D shifts by 2 to F, O shifts by 0 to O, and G shifts by 19 to Z.

Question 8

Use a Vigenere cipher to encrypt MATH with the key KEY. Repeat the key as KEYK.

Accepted Answer

The encrypted message is WERR because M shifts by K to W, A shifts by E to E, T shifts by Y to R, and H shifts by K to R.

Question 9

Use a Vigenere cipher to decrypt RIJVS with the key KEY. Repeat the key as KEYKE.

Accepted Answer

The decrypted message is HELLO because R shifts back by K to H, I shifts back by E to E, J shifts back by Y to L, V shifts back by K to L, and S shifts back by E to O.

Question 10

Write the repeated Vigenere key for the plaintext SCIENCE if the key is MATH. Then give the shift value for each key letter.

Accepted Answer

The repeated key is MATHMAT. The shift values are 12, 0, 19, 7, 12, 0, and 19.

Question 11

Explain one way a Vigenere cipher is different from a Caesar cipher.

Accepted Answer

A Caesar cipher uses the same shift for every letter, but a Vigenere cipher uses a repeating key that can give different shifts to different letters.

Question 12

Use a Vigenere cipher to decrypt LXFOPV with the key LEMON. Repeat the key as LEMONL.

Accepted Answer

The decrypted message is ATTACK because each cipher letter is shifted backward by the matching key letter in LEMONL.

Cryptography: Caesar and Vigenere Ciphers

More Math Worksheets

More Grade 6-8 Worksheets