The Caesar Cipher Do-Over (WS #1)

Julius Caesar used a extremely simple substitution cipher to send messages to his troops. He substituted each letter by the letter that was 3 places further along in the alphabet, so that “a” was replaced with “D”, “b” with “E” and so on. This is a substitution cipher with a key of 3.

Using a key of 4, tell me what the encrypted letters are for these plain text letters (print out the Caesar Cipher tables attached to this lesson to help you decode and encode the messages.)

A, D, L , P, X and Z

In a Caesar Cipher each letter in the plain text is shifted from 1 (Plain text A = Cipher B) to 25 (Plain text A = Cipher Z) places in the Cipher text.

To encrypt, shift each letter up the alphabet according to the key.

To decrypt, just shift each letter down the alphabet according to the key.

a. With a key of 10, plain text A would be encrypted to what encrypted letter?

b. With a key of 7, encrypted letter x becomes what plain text letter?

Computer scientists would call 3 the “key” for this cipher. How many different keys are possible in the English alphabet?

Convert "GJGB" cipher-text back into plain text using the key: 1

• FIFA

• DUKE

• YALE

• BAMA

Convert "VOOVXF" cipher-text back into plain text using the key: 20

• ATTACK

• ANIMAL

• CHARGE

• GIVEUP

Encrypt the plain text word 'COVID" with a key of 7.

Convert "OQQC" cipher-text back into plain text using the key: 10

• DATE

• MILK

• EGGS

• HAMS

Bletchley Park is a 19th-century mansion and estate in Buckinghamshire, England that became the principal centre of Allied code-breaking during the Second World War.

During World War II, the estate housed the British Government Code and Cypher School (GC&CS), which regularly penetrated the secret communications of the Axis Powers--most importantly the German Enigma and Lorenz ciphers.

According to the official historian of British Intelligence, the "Ultra" intelligence produced at Bletchley shortened the war by two to four years, and without it the outcome of the war would have been uncertain.

Which of the four answers below is the corrcetly encrypted text for Bletchly Park?

• Rbujsxbuo Fqhb

• Rhujsxbuo Fqha

• Rbujsxbuo Fqha

• Rrujsxbuo Fqha

"Manchester City FC" is plain text and the cipher text is: "Bpcrwthitg Rxin UR" - What would the encryption key be?

• 15

• 10

• 12

• 4

Using the Caesar Cipher, encode the name of your school with a Key = 3