How to Make a Secret Decoder
A secret decoder is a simple cryptographic device consisting of two discs attached to each other through their center and able to rotate independently. Secret decoders use simple substitution cyphers which can be easily broken with some effort. Making a secret decoder requires only a handful of supplies and can be a good project for children who want to write messages in a secret code to prevent other people from reading them.
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Things You'll Need
- Colored and white card stock
- Compass
- Scissors
- 1/4-inch hole punch
- Glue stick
- Brass fastener
- Pen
- Paper
- Fine tip marker
Instructions
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Draw a circle with a 2-inch radius on the colored card stock using the compass.
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Draw a circle with a 1.8-inch radius on the white card stock using the compass.
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Draw a circle with a 1.4-inch radius on the colored card stock using the compass.
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Cut out all three circles with the scissors.
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Punch a single hole close to the edge of the small colored circle with the hole punch.
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Glue the white circle in the center of the large colored circle, using the hole left by the compass as a guide to place the white circle precisely.
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Attach the small colored circle to the glued-together circles by pushing a brass fastener through the hole left by the compass, using the scissors to widen the hole slightly if necessary.
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Write the alphabet on a piece of paper in a single row. In a second row, underneath each letter, write the letter or symbol that you would like to have correspond to it. For example, for a simple alphabetic substitution cypher, you can use the letter "P" to mean the letter "A," then move in order through the alphabet, using "Q" for "B," "R" for "C," "S" for "D" and so on.
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Write the first letter or symbol of the second row of your sheet of paper on the outer portion of the white circle, right above the hole in the middle circle, using the fine tip marker. Write the letter that corresponds to it on the part of the white circle that is showing through the hole in the middle circle. For example, you would write "P" on the outer portion of the white circle and "A" on the part that is showing through the hole.
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Rotate the middle circle to the right until the first letter you wrote has just completely disappeared. Write the second letter or symbol of the second row of your sheet of paper on the outer portion of the white circle, right above the hole in the middle circle. Write the letter that corresponds to it on the part of the white circle that is showing through the hole in the middle circle. For example, you would write "Q" on the outer portion of the white circle and "B" on the part that is showing through the hole. Repeat this process until you have written down all the letters and symbols in your cypher.
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Tips & Warnings
Keep the sheet of paper with the key to the cypher in case you want to make more secret decoders for the same cypher.
References
- Photo Credit Jupiterimages/liquidlibrary/Getty Images
