Grille Cipher

What You Need:

  • White paper
  • Brightly colored paper
  • Pen
  • Pencil
  • Craft knife
  • Magazine
  • Computer
  • Printer

What You Do:

  1. Before you can practice using a grille cipher (or any cipher), you need to have a secret message. What will your child's message be? Help him brainstorm his message before writing it down on a piece of paper.
  2. Next, your child will need to hide his message inside a longer letter. Encourage him to make the topic of the letter entirely different than the topic of his secret message. This will make it harder for others to guess what the message is.
  3. Hiding the secret message in the letter will seem like a big job, but it isn’t if he just takes it one word at a time. For his first grille cipher, a good rule to follow is one sentence per word in his secret message. For example, if his first secret message word is "take," he'll need to write a whole sentence to hide only that word. Something like this would work: "I'm not sure if I really enjoyed the Chinese take-out food we ate last night."
  4. Have your child write this note out on the computer.
  5. Print the note on a sheet of white paper.
  6. Now it is time to make the grille.  The grille is the decoder for the letter.  Without the grille, no one -- not even your child’s friend -- will see the secret part of the message. 
  7. Have your child lay a piece of brightly colored paper over the letter. 
  8. Let him hold both pieces of paper up against a window. Make sure the papers are properly layered over each other. 
  9. Help him use a pencil to draw a box on the bright paper around each word of his secret message.
  10. Each penciled box will be cut out with the craft knife. Either help your child do this or take over the cutting duties. Crafting knives can be dangerous, and it might be best to have your child sit out this step.
  11. Place the brightly colored paper on top of the magazine. The magazine will serve as a protective surface.
  12. Carefully use the craft knife to cut the penciled boxes.
  13. Have your child test out the grille cipher. Show him how the brightly colored paper blocks out all the other words, except for the words that make up the secret message.
  14. The final step is for your child to give both the letter and the grille to his friend. Do you think he'll be able to figure out the secret message?

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