The Caesar Cipher (What it Is and How to Teach Your Kids)

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My kids have big imaginations. I mean, who hasn’t dreamed of sending secret messages like a spy or decoding a secret pirate map? If I’m honest, I have dreamt about living out my own personal National Treasure (that is, without the bad guys shooting at me and all).

The good news is, there are some super easy secret codes and ciphers you can teach your kids right now. One of the easiest ciphers you can learn is the Caesar Cipher. 

This article is originally from www.dadstuffsite.com

What is a Caesar Cipher (Caesar Shift, Caesar Substitution, Shift Cipher, Rot-n Cipher)

A Caesar cipher (also known as a Caesar shift, Caesar substitution, shift cipher, or a ROT-n cipher, short for rotation by n letters), is a simple substitution cipher. It is made by shifting each letter of the alphabet a predetermined number of places, or rotations (ROT for short). For example, in a ROT1 shift, the letter A becomes B, B becomes C, etc. 

In a substitution cipher, the order of letters in the original message (or plaintext) remains the same. Each letter is substituted by another letter or symbol into a coded message (or cipher text). 

The Caesar cipher gets its name from the Roman Emperor Julius Caesar. Caesar used it to disguise his personal correspondence and to protect sensitive military messages. While easy to decode by today’s standards, it was reasonably secure in his time because many of Caesar’s enemies were illiterate.

The Caesar Cipher is “monoalphabetic” in that each letter is replaced by one and only one letter or symbol. Therefore, Caesar Ciphers are easy to break. While not used in professional cryptography anymore, Caesar Ciphers are fun to do and super easy to teach your kids

This article is originally from www.dadstuffsite.com

If you want to learn about another cipher used in history, check out The Ottendorf Cipher (What it Is and How to Teach Your Kids).

How to Encode and Decode Messages Using a Caesar Cipher

The basic premise of a Caesar Cipher is to take two alphabets, one written above the other. You then shift one alphabet over a predetermined number of spaces. 

In the example below, the top alphabet shifts 3 spaces to the right. It is called a ROT3 cipher because the alphabet rotates 3 spaces. (This will make more sense when we talk about the cipher wheel). 

To encode—that is, to convert the plaintext message into ciphertext—take the corresponding letters of your message from the top row (plaintext) and replace them with the letters of the bottom (ciphertext). 

Using the diagram with a key number rotation of 3 (or ROT3), we can encode the following message:

“Dad jokes are how I keep from crying”

First, find the letter D in the top row and replace it with the letter G in the second row. The second letter A will be replaced with D, and so on. 

Plaintext:   dad jokes are how i keep from crying

Ciphertext: gdg mrnhv duh krz l nhhs iurp fublqj

This article is originally from www.dadstuffsite.com

To decode, simply work the other way. Take the corresponding letters of your coded message from the bottom row (ciphertext) and replace them with the letters of the top (plaintext)

While all of this is pretty straightforward, remember not to mix up your plaintext and ciphertext rows when encoding and decoding. I almost messed up an awesome treasure hunt I made for my kids by explaining it to them backwards. Oops. 

If you’re interested in more secret codes, check out The Rail Fence Cipher (Fun Secret Code to Teach Your Kids).

How to Use a Caesar Disk (ROT-n Cipher Disk)

A really simple way to encode and decode your messages is using a cipher disk. There are a number of free printable disks online, but most are missing the ROT number on the wheel. This number makes decoding much easier. 

Here’s a free downloadable cipher wheel pdf. I promise it’s not clickbait and I won’t make you sign up for my email list (I hate that). Just print it out and enjoy.

If you want to go extra and want something fancy to hand your kids, you can also buy a cipher disk. You can find a lot of wooden disks on Amazon and Etsy. I personally like this one because, once again, it has the ROT number, making decoding much simpler.

Another great cipher that uses a decoder is the Scytale Cipher. To learn more, check out The Scytale Cipher (What It Is and How to Teach Your Kids).

Caesar Cipher Activity Ideas (Plus a Free Worksheet)

The good news about a Caesar Cipher is that it is easy to teach your kids without much (or really any) explanation. With the help of a cipher disk, you can simply hand your kid a coded message with a given ROT number. Assuming they know their letters, they should be able to decode the message without knowing any of the explanation behind the cipher itself. 

When thinking of activities to do with your kids, you can always start with something as simple as a worksheet. This always seems a bit homework-y to me, but some kids are like Hermione Granger and like doing homework. To each their own. 

This article is originally from www.dadstuffsite.com

Here are some free downloadable worksheets you can work on with your kids. 

Learn more: 6 Secret Codes and Ciphers to Teach Young Kids

Another idea is to have your kids write a coded letter to their grandparents, or vice versa. My kids love having their grandparents as pen pals, and their grandparents love being able to participate in an activity with them (especially since the nearest grandparent is about 900 miles away).

But the best idea, the most Dad-Stuff-extra idea, the one that gets me personally excited, is the treasure hunt. 

First I placed some cleverly written clues around the house on what looks like really old paper. (Weathering the paper is not necessary, but I was having fun! Check out How to Weather Paper to Make it Look Old (The Ultimate Guide)). Then I dropped the first clue and cipher wheel in an out-of-the-way spot that I knew my kids will discover.

This definitely takes a little more preparation, but worry not! Check out the article I made about my epic Caesar Cipher Treasure Hunt for all the details. You can find out how make your own clues (and go the extra mile) or use my clues to recreate my treasure hunt. 

My kids had a blast, and it kept them busy and excited the entire morning. The side benefit I found with this treasure hunt was that my kids were both mentally and physically spent. At the end of the day they were spent and super chill. Win-win!

This article is originally from www.dadstuffsite.com

You might also like these Treasure Hunt activities:

• A Christmas Treasure Hunt (For the Whole Family)
• Ottendorf Treasure Hunt Activity to Do With Your Kids
• Become Penpals with an Alien (Pigpen Cipher Activity)
• Book Cipher Treasure Hunt Activity to Do with Your Kids