Aidan (age 10) really enjoys secret codes, and we were thrilled to find this idea on Spoonful for making a spy decoder! The fun part about this decoder is that it provides 27 different codes, making it difficult for someone to crack. If you make two identical decoders, siblings or friends can send encrypted messages to each other.
To make a decoder, you will need:
- Colored pencils
- A compass
- A pencil
- A ruler
- A paper fastener
- A fine tip Sharpie marker
Step 1: Cut out three circles per decoder out of posterboard. You will need one that is 3.25 inches in diameter, one that is 2.5 inches in diameter, and one that is 1.5 inches in diameter.
Note: The size of the circles is very important! If you change the size of the decoder, you will have to change the measurements for marking off the letter sections, which involves higher level math than I felt like using…
Step 2: Color your circles with colored penciles, if desired.
Step 3: On the largest circle, make small pencil marks 3/8″ apart on the outside edge. You should end up with 27 sections.
Detail is important in this step! This was where we got into trouble. We were trying to make three identical decoders. I had 28 sections on my first try, and Aidan had 24. Obviously, those two decoders were not going to be compatible! We figured out what we were doing differently, and we decided that I would make all of the outside pieces so that they would be the same. We had to start over on the large circles, and I made 3 with exactly 27 sections each.
Step 4: Poke a hole through the center of the largest circle and the middle circle. Attach them with the paper fastener. The best way to find the middle of the circle is to use the compass.
Then, use the ruler to draw a straight line from the paper fastener to each edge mark. Again, detail is important. You really want each of the sections to be equal in size, or your decoder will be difficult to use.
Step 5: Write the alphabet on the outside circle and put a ? in the 27th section. For the middle circle, you can either write the alphabet in order or mix it up. Aidan wanted a random alphabet in the middle circle – I think it made it feel more secret!
Then add the smallest circle to the decoder.
To write a message:
First, set the code. The post on Spoonful suggests setting the decoder where the “A” on the outside circle matches the first letter of the day of the week. Aidan wasn’t wild about that idea. We thought of sending a “code word” along with each message and setting the decoder where “A” on the red circle matches the first letter of the code word. Or, come up with your own system!
To write a message, find the letter you want on the outside (red) circle and write down the corresponding letter on the middle (blue) circle.
To read a message, find the letter on the middle (blue) circle, and write down the corresponding letter from the outside (red) circle.
The post on Spoonful has additional directions for making the decoder into something that can be worn around your neck – kind of fun if you want to add that step!
The Thomas Jefferson Cipher Wheel – Here’s an interesting tidbit from history… Thomas Jefferson created a cipher wheel which was used to send encrypted messages in a similar way. The wheel was made from 36 discs on an axle that could be turned to spell out a message. To encrypt the message, the sender would copy down any other row from the cipher wheel other than the intended message (which would appear to be nonsense). The receiver would line up the discs on his (identical) cipher wheel so that they matched the nonsense message and then turn the cipher wheel until they saw a row with the hidden message. Click here to read more about the Jefferson Cipher Wheel – it’s quite interesting! You can also purchase a replica (that really works) from monticello.org.