Some information on computers needs to stay secure. You definitely don’t want everyone to know your password! How do you send information that can only be read by certain people? Long before computers were invented, people came up with tricks to make sure their private information stayed private.

Encryption is a way to hide a secret in plain sight. One very old encryption is called a shift cipher. Using a grid, you shift (or move) every letter in the alphabet a few spaces over. The number of spaces the letters were shifted is called the “key.” If you know the key, then you can break the code to read the message. If you don’t know the key, you can’t understand the message. Look at this alphabet that has been shifted over four spaces. The key for this cipher is 4. Cipher chart shifted 4 spaces

Use the above chart to decrypt this message. Find each letter in the chart and write down the matching letter. Encrypted message CSY JSYRH QC WIGVIX There’s a special tool for this kind of encryption called a cipher wheel. You can set the key for your cipher by spinning the wheels. When they are lined up right, you can encrypt and decrypt messages.

Instructions

Build the cipher wheel

  1. Glue the cipher wheel page of your booklet to a piece of cardboard (like a cereal box).
  2. Let the glue dry and cut out the two circles.
  3. Lay the small circle on top of the larger one.
  4. Stick a tack, pencil, or paperclip through the center to hold the two circles together
  5. Turn the inner circle to line up the key number with the A on the outside circle.
  6. Use your cipher to decrypt the messages on page 7 of your worksheet.
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