Practice using Caesar ciphers and Vigenere ciphers to encrypt and decrypt short messages with modular arithmetic.
Read each problem carefully. Use A = 0, B = 1, C = 2, and so on through Z = 25. For Caesar ciphers, shift each letter by the given number.
For Vigenere ciphers, repeat the key as needed and shift by each key letter. Ignore spaces and punctuation unless the problem says otherwise.
Encoding and decoding messages with alphabet shifts
Math - Grade 6-8
- 1
Use a Caesar cipher with a shift of 3 to encrypt the word MATH.
- 2
Use a Caesar cipher with a shift of 3 to decrypt the message KHOOR.
- 3
Use a Caesar cipher with a shift of 5 to encrypt the word CODE.
- 4
Use a Caesar cipher with a shift of 3 to decrypt the message FUBSWR.
- 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?
- 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?
- 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.
- 8
Use a Vigenere cipher to encrypt MATH with the key KEY. Repeat the key as KEYK.
- 9
Use a Vigenere cipher to decrypt RIJVS with the key KEY. Repeat the key as KEYKE.
- 10
Write the repeated Vigenere key for the plaintext SCIENCE if the key is MATH. Then give the shift value for each key letter.
- 11
Explain one way a Vigenere cipher is different from a Caesar cipher.
- 12
Use a Vigenere cipher to decrypt LXFOPV with the key LEMON. Repeat the key as LEMONL.