- Age:7+
- Time:30 min
- Difficulty:Easy
- Mess level:Low
- Supervision:Yes
🔐 Encode as you read
✂️ Free printable
Cipher wheel template
2 pages · 138 KB
Two ready-to-cut wheels plus assembly steps and secret-code instructions - print, cut, pin, and start encoding.
What is Cryptography?
Cryptography (cryptology) is a study of ways to conduct secure communication. More precisely, cryptography is investigating ways to encrypt and decrypt messages so they stay private and deals with developing protocols that can help with that. Word cryptography comes from the Greek words kryptós, which means “hidden” and graphein, which means writing.
History of Cryptography and Message Coding
Cryptography has been used from ancient times since there was always a need for keeping certain messages private. Oldest ciphertext comes from Egypt and is dated 1900 BCE, but different ways to encode messages have been found in various cultures, from Greece and Persia to India.
One of the more popular substitution ciphers, the Caesar cipher, is named after Julius Caesar, who used it to send secret messages to his generals - the Roman writer Suetonius describes exactly how. Caesar probably didn't invent it, since simple shift ciphers were likely around before him, but his name stuck. It is also known as the Shift Cipher.
One of the first ciphers was a Caesar Cipher or Shift Cipher that used crude, but an effective algorithm.
In modern history, the most famous encrypting example was the Enigma machine which Germany used to encode their messages during World War 2. The British bombe, a decrypting machine designed by Alan Turing at Bletchley Park and much improved by Gordon Welchman, had a tremendous impact on ending World War 2. It built on an earlier Polish machine, the bomba, created by Marian Rejewski's team before the war.
Today, lots of time and effort has been put in finding new and better ways to secure our communication and privacy. Cryptography is especially important in the field of internet security because of the huge amount of data flowing on the internet today and the danger of hacking private data.
Different ways of Encrypting Messages
In the past, cryptography focused on the ways to make certain messages (plaintext) incomprehensible (ciphertext). The reverse process, called decryption, translates ciphertext back into the plaintext.
The first methods to encrypt the messages were transpositions, the simple scrambling of the letters in the sentence (anagram). After that came the substitution cipher, where every letter is swapped for another letter or symbol according to some rule - the rule can be anything you like, as long as both sides know it. The shift cipher is the simplest kind of substitution: it uses a key (a number) and moves every letter that many places along the alphabet (example: A becomes D if the key is 3).
Caesar cipher is an example of a substitution cipher. This key should be kept private between people involved in communication. However, this method is quite prone to brute force attacks, since there is a limited number of possible keys.
Later there were different methods where the key was a word. That was more secure, but still not too hard to crack.
In the modern age, with the powers of computers, we need much better ways to encrypt pieces of information. The big breakthrough was changing from the symmetrical key (both sender and recipient have the same key) to the asymmetric or public key.
In this system, the public key, which is used for encryption is freely distributed and it's paired with a private key. The private key is used for decryption and it needs to stay secret. This change had a tremendous impact on increasing the security of our communication.
Today Cryptography got more sophisticated to protect information from possible theft.
No doubt, this field will continue to evolve, since the methods of hackers who want to get to our private information are also getting better.
But let us take a trip to history and make our own cipher wheel in a way that Julius Caesar did.
Try it right now! Type a message, pick a shift, and watch it scramble into a secret code:
Tip: tell your friend the shift number so they can decode it.
Shifts the 26-letter alphabet A–Z. Spaces and punctuation stay the same.
Materials needed to make a Cipher Wheel
We need some simple household materials to make a perfectly usable Cipher Wheel.
- Cardboard. We will use cardboard to make the spinning wheels for our cipher. The regular cardboard box will do nicely. We can also use plain paper, but thicker materials such as cardboard would be easier to work with.
- Compass. We will use the compass to create two circles on our cardboard. One smaller and one larger. They will be the base for our cipher wheel.
- Scissors. And we can’t cut the circles from cardboard without scissors. Instead of scissors, we can also use a scalpel if it is more convenient.
- Ruler. We will use a ruler to create equal fields on our cipher wheel. The ruler is great since we can pull straight lines across both wheels we created from cardboard. Here, we can also use the Protractor to measure equal fields and create supporting lines that we will connect with the ruler.
- Pin. We need one pin to connect smaller and bigger cardboard circles so we get the spinning wheel.
- Pencil. We will need a pencil to draw lines and create fields on our cipher wheel. Also, we will need it to write letters that we will use to decrypt the message.
- Colored pencils or Markers. We can use different colored pencils or markers to decorate our cipher wheel. They are not mandatory, but will surely make our wheel look great.
Instructions on making a Caesar Cipher Wheel
You can watch the video at the beginning of an article to see the creation of a cipher wheel in action, or continue reading for step by step instructions on how to make one.
- Take one piece of cardboard and a compass. Spread the compass to its maximum radius and draw a circle. The circle of around 20 cm will be good for our larger circle, but you can make it even bigger for a bigger cipher wheel.
- Take the second piece of cardboard and a compass and draw one smaller circle. You can use the ruler to measure a few centimeters smaller radius. 3-4 cm smaller radius than the first circle will suffice.
- Cut both circles using scissors or scalpel.
- Take one pin and connect a smaller circle to the bigger circle by pinning them together in the center. For now, we should remove the pin because we just wanted to create a little hole to mark a center. So, remove the pin but keep circles as they were - smaller on the bigger in the center.
Our cipher wheel in the making: both cardboard circles divided into fields, one for each letter.
- Method 1, without protractor: Take the ruler and a pencil, and draw a horizontal and vertical line that goes through the center (where is the hole from the pin). Now we have split both of our circles on 4 parts. Draw 2 more lines, this time diagonally. Now we have split the circles into 8 parts. Now draw more lines in the middle of each field to get 16 parts. And one more time to get 32 parts. That is enough to fit the whole alphabet.
- Method 2, with protractor: If you have a protractor, now it would be a good time to use it. You can create the fields that are the same size, no matter how many fields you need. For example, if you want to have 26 fields to fit all letters of the English alphabet, you can divide 360 by 26 (360 degrees/26 fields=13.85). So we should draw a line on every 13.85 degrees around our cipher wheel.
- Now again use the pin to connect the smaller wheel on the bigger one. This will allow the smaller wheel to rotate inside the bigger wheel.
- Write the letters of the alphabet into the fields of both circles in the same order. If there are any excess fields left, you can draw any shape or leave empty.
- Color and decorate your wheel using colored pencils or markers and you are ready to cipher and decipher secret messages!
How to use a Cipher Wheel (Caesar Cypher)
Both sender and receiver need to know the key and they can use the Cipher wheel to send secret messages.
Encrypting the message
Decide on a key you will use. For example, let’s say the key is 5 - right.
Write down the key, and the person you are sending the message to, the one who will decrypt the message, needs to know that key. Align both circles of the cipher wheel. So the same letter on the smaller circle needs to be below that letter on the bigger circle.
Now move the smaller (bottom) circle for a key number of times in the direction that is on the key. In our example, where the key is 5 - right, A will become F (B -1, C-2, D-3, E-4, F-5).
Write down on the paper your ciphertext from the smaller circle. We find the letter we want to encrypt on the big circle and write on the paper corresponding letter (encrypted letter) from the smaller circle.
Decrypting the message
You got a secret message! Awesome. You need to know the key by which the message is encrypted. So you got some gibberish on the paper and the key that says 5 - right.
Take your wheel and align it so there is the same letter on top and on the bottom circle.
Now move the smaller (bottom) circle for a key number of times - 5 times to the right. Look at the encrypted letter from the paper on a smaller circle and write down the corresponding letter on the big circle above it. When you finish with all the letters, you will know your message!
A Caesar cipher shifts every letter by a secret key. How many different keys would you have to try to crack it by hand?
Make your prediction, then tap an answer to check!
Crack a message without the key
Here's the game that teaches the most, and it needs no extra materials: give your child a message without telling them the key. Can they read it anyway?
They can - and that's the point. A Caesar cipher has only 25 possible keys (shifting by 26 just gets you back where you started). So you simply try them all: set the wheel to 1, decode the first word, is it gibberish? Try 2. Try 3. Long before you reach 25, a real word jumps out and the whole message unlocks. This is called a brute force attack: not clever, just stubborn. Most children crack their first message in a couple of minutes, and it is genuinely thrilling.
That leads straight to the real lesson: a code is only strong if trying every key is too slow to be worth it. Twenty-five keys is nothing. Modern encryption uses so many possible keys that every computer on Earth working together would still be at it long after the sun burns out. Same idea as your wheel - just a bigger number.
For older kids: cracking it without even trying
There's a smarter attack, and it feels like magic. In English, E is by far the most common letter. So take a long enough coded message and count which letter appears most - it's almost certainly E in disguise. Count the gap from that letter back to E, and you have the key on the first guess, without trying anything. That's frequency analysis, invented over a thousand years ago by the Arab scholar al-Kindi, and it's the reason simple substitution ciphers were doomed. Try it: encode a paragraph, then count letters and see if you can find the key.
What will you Develop and Learn
- Basic cryptography knowledge - encrypting, decrypting, algorithms.
- Why codes break - brute force, and why key count is what makes a cipher strong.
- Engineering skills - by designing and making your own encrypting tool.
- Math skills - using the key we need to count.
- Alphabet - Writing and reading letters to encrypt and decrypt messages.
- Logical skills - by thinking of system to encrypt messages and reading the key we need to decrypt them.
- Hand-eye coordination - lining up and turning the wheel is precise, fiddly work.
Key takeaways
- A cipher wheel is a two-disc cardboard tool for encrypting and decrypting messages with the Caesar (shift) cipher.
- The key is a number: you shift every letter that many places along the alphabet (with a key of 5, A becomes F).
- Both sender and receiver need the same key - this is called symmetric encryption.
- The Caesar cipher is weak because it has only 25 keys: you can brute-force it by trying them all, or use frequency analysis (E is the most common English letter) to find the key in one guess.
- The activity teaches real cryptography, engineering, and math ideas - including why a code is only as strong as the number of keys an attacker must try.
Frequently Asked Questions
What is a cipher wheel?
A cipher wheel is a simple tool made of two rotating discs marked with the alphabet. By turning the inner disc, you line up each plain letter with a coded one, letting you quickly encrypt and decrypt messages using the Caesar (shift) cipher. You may also see it called a decoder wheel, a Caesar cipher wheel or a secret decoder ring.
What is the Caesar cipher?
The Caesar cipher, named after Julius Caesar, is a substitution cipher that shifts every letter a fixed number of places along the alphabet. That number is the key - for example, with a key of 3, A becomes D, B becomes E, and so on.
How do you make a cipher wheel?
Cut two cardboard circles, one a few centimetres smaller than the other. Divide each into equal fields (using a ruler or protractor) and write the alphabet around both in the same order. Pin them together through the centre so the inner wheel spins, then decorate it.
How do you use a cipher wheel?
Agree on a key with the person you're writing to, for example 5 to the right. Line the two wheels up so the same letters sit above each other, then turn the inner wheel by the key. To encode, find each letter of your message on the outer wheel and write down the letter beneath it. To decode, do the reverse: find the coded letter on the inner wheel and read off the letter above it.
How do you crack a Caesar cipher without the key?
Because there are only 25 possible keys, you can simply try each shift until real words appear - a brute-force attack that usually takes a couple of minutes. For longer messages, frequency analysis is even faster: the most common letter is almost always E in disguise.
What is frequency analysis?
Frequency analysis is cracking a cipher by counting how often each letter appears. In English, E is by far the most common letter, so the most frequent letter in the code is probably E. The gap between them reveals the key. The Arab scholar al-Kindi described it over a thousand years ago.
What age is the cipher wheel activity for?
Around ages 7 and up. Making the wheel involves scissors (or a scalpel) and a pin, so an adult should help with cutting for younger children. Once built, encoding and decoding messages suits a wide range of ages, right up to adults.
If you are interested in more fun activities from technology and math without using the screen, check out:
- How to make Hanoi tower for an excellent logical puzzle that can be easy or hard as much as you want.
- Explore the mysterious Number Pi (Π) to learn about this fascinating number and an easy way how to demonstrate it.
- Fun activities for practicing Matching Patterns to improve logical skills and the activity is suitable even for the youngest audience.
- How to Make a Cardboard Clock and Learn to Tell the Time is a great activity to teach children about clock and time in a fun way. And you already have all materials you need.
- Or you can go a bit more advanced and learn how to make your own projector from cardboard and watch videos on a big screen anywhere.
