Cipher Wheel

What you need:
• Poster board or two small paper plates
• Scissors
• Ruler or compass
• Pencil
• Brass paper fastener
• Ballpoint pen

What you do:
• Cut two circles (1- 6 inches, 1- 4 inches), from poster board. (You can also use two small paper plates.)
• Cut a 1/2-inch-wide V-shape and a 1/2-inch-round window in one circle wheel, as shown.
• Use the pencil to poke a small hole in the center of both wheels.
• Attach the wheels with a brass paper fastener.
• Divide the circles into 26 spaces with a ruler.
• Write the alphabet A to Z on both circles.

Make a second wheel for your friend that matches yours exactly so you can write and decode secret messages.

N.B.: The cipher disk (wheel) was invented in 1467 by Leon Battista Alberti, a famous Italian philosopher and architect.
Alberti used two different alphabets located on concentric rings – this means one ring is inside of or on top of another. By lining up two different letters, one from each ring, he could make a simple substitution alphabet in which he could create a cipher.
For example, if he aligned the A on the outer ring with the G on the inner ring, this would make the following substitution alphabet used to encrypt a message:

OUTER RING: ABCDEFGHIJKLMNOPQRSTUVWXYZ
INNER RING: GHIJKLMNOPQRSTUVWXYZABCDEF

From there, he could encrypt his message and send it to someone who knew the secret to revealing the message.