History of Cryptography & Caesar Cipher

Step 1: Choose a number between 1 and 25. This is the key. It will determine how each letter of the alphabet will change.

Step 2: Grab your cipher ring. Line it up so the top and bottom alphabet are the same. A above A, B above B, etc. The ring will look like this:

Step 3: Rotate the top alphabet ring a number of spaces equal to the key. This is known as a shift. For example, if the key is the number 1, then shift the top alphabet row to the right by 1 letter. The ring should then look like this:

Step 4: Now that the ring is shifted, do not rotate it any more. You can encrypt your message by looking at the message letter by letter. Find each letter on the top ring and change it to the letter directly below it. For example, if letter A is on top of letter B, then A turns into B when encrypted. The direction of a shift in the Caesar cipher does matter. 

To decrypt a message using the cipher rings, steps 1-3 are the same. The only difference is you look at the encrypted message letter by letter, and you find each letter on the bottom row and change it into the letter above it on the top row.

You will use the Caesar cipher ring to decrypt messages. Let’s start with a simple shift of 1. Remember, to decrypt the message, shift the top of the ring 1 space to the right where ‘A’ is on top of ‘B’. You will feel and hear a click with each rotation.

• The encrypted message is: HFODZCFS

• The key is: Rotate 1

After you rotate the ring, decrypt the message by changing each letter of HFODZCFS into the letter directly above it. 

Puzzle 1: What word does HFODZCFS decrypt into?

Not too bad, right? Let’s try a harder one. This next one has a shift of 3. Remember to reset ‘A’ on top of ‘A’ before shifting! Your cipher ring will look a bit different after the shift.

• The encrypted message is:  FRQILGHQWLDOLWB

• Key:  Rotate 3

Remember, to decrypt, change the bottom letters to top letters. 

Puzzle 2: What does the word FRQILGHQWLDOLWB decrypt into?

Great job! Let’s decrypt one more message knowing the key size.

The encrypted message is:  OQXOPEPQPEKJ

Key:  Rotate 22

Puzzle 3: What does the word OQXOPEPQPEKJ decrypt into?

In brute-force decryption, you only have knowledge of the ciphertext, so you have to guess the value of the key until you get a legible plaintext that makes sense.

In normal cryptography, brute-force attacks are not effective unless you have a small key size. Luckily for you, the Caesar cipher can only encrypt a message in 25 different ways. That means in the worst case, you’ll have to try 25 different keys to decrypt the message. However, there is a trick to solve this message in only one or two attempts. Can you figure it out?

• The encrypted message is: A SE S UGVWTJWSCWJ

• Key:  Unknown

Puzzle 4: What does the phrase A SE S UGVWTJWSCWJ decrypt into?

Puzzle 5: What is the key (shift value)?

For those who love a challenge, let's see if you can figure out this message without any hints or keys. Unfortunately, the same trick won't work here. 

• The encrypted message is: PNZC FUVEG FRPERG PBQR

• Key:  Unknown

Puzzle 6: What does the phrase PNZC FUVEG FRPERG PBQR decrypt into?

Follow the steps below to encrypt a message for another camper. Remember, when encrypting, you change letters from top to bottom. Only decryption goes from bottom to top.

Create your own appropriate original message. 

Puzzle 7: What is the message?

Decide on a key for the shift.

Puzzle 8: What is the key?

Encrypt the message using the key. 

Puzzle 9: What is the encrypted message?