Cipher Wheel Cryptography Challenge
Build a rotating cipher wheel and use it to encode and decode secret messages. Learn the same encryption principle that Julius Caesar used to protect military secrets.
What You'll Need
- 1Cardstock (2 sheets)
- 2Scissors
- 3Brass fastener (brad)
- 4Ruler and pencil
- 5Marker for writing letters
What You'll Need
Cardstock (2 sheets)
Scissors, ruler, pencil
A brass fastener (brad)
A marker for writing the alphabet
How to Play
Cut two circles: one large, one slightly smaller. Write A-Z around each edge.
Pin them together through the center with a brad so the inner wheel rotates.
Set a key: rotate so A aligns with D (shift of 3). "This is our secret key."
Encode: H on the outer wheel = K on the inner. HELLO becomes KHOOR.
Pass the encoded message to a friend with the key.
Decode: K on the inner = H on the outer. KHOOR becomes HELLO.
Try different shifts. "Why is a shift of 1 easy to crack?"
The Math Behind It
This is a Caesar cipher, named after Julius Caesar who used it for military communications. Mathematically, each letter is shifted by a fixed number (the key). With 26 letters, there are only 25 possible shifts — making it easy to crack by trying all possibilities (brute force). Modern encryption uses this same substitution principle but with keys so long that brute force would take millions of years.
Tips
Space the letters evenly around the circle. Use a protractor for precision: 360/26 = about 13.8 degrees per letter.
Start with short messages (3-5 words). Long messages take patience.
Challenge your child to crack a message WITHOUT knowing the key. (Hint: E is the most common letter in English. Find the most common letter in the coded message, and assume it's E.)
This is the perfect entry point into computer science discussions about cybersecurity and encryption.
Try double encryption: encode a message with shift 3, then encode THAT result with shift 5. Cracking it requires knowing both keys.
Frequently Asked Questions
How long does this activity take?
This activity takes about 30 min, with 15 min of preparation time beforehand.
What materials do I need?
You'll need: cardstock (2 sheets), scissors, brass fastener (brad), ruler and pencil, marker for writing letters.
What age is this activity for?
This activity is designed for 8-12 years. You can adapt it for younger or older children by adjusting the complexity.
Can this be done indoors?
This activity is designed for indoor play, making it perfect for rainy days or when you're staying inside.
How difficult is this activity?
This activity has a moderate difficulty level. It may require some preparation or guidance, but is manageable for most families.
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