← CS Unplugged

CS Unplugged activity

Caesar Cipher: the optional wheel

An optional dial for the Caesar cipher activity. Everything on that sheet works with its fill-in shift table, so only print this if you’d rather turn a dial than write out an alphabet. It needs scissors and a brad (or a pencil point).

OPTIONAL: the cipher wheel

Everything on this page also works with the shift table, so only build this if you would rather turn a dial than write out an alphabet. This is the one page in this whole activity where you need scissors.

  1. Cut out the big wheel (the solid outline) and the small wheel (the dashed outline).
  2. Stack the small wheel on top of the big wheel, both letter side up, with their center marks lined up.
  3. Push a brad through both center marks, or hold a pencil point steady there while you turn the small wheel. Either way, the small wheel needs to spin freely around that one point.
ABCDEFGHIJKLMNOPQRSTUVWXYZ 012345678910111213141516171819202122232425
Big wheel: cut all the way around the solid outer line. The small numbers are the key, 0 through 25.
ABCDEFGHIJKLMNOPQRSTUVWXYZ
Small wheel: cut around the dashed line instead, so you can tell it apart from the big wheel once both are cut out.

To encode with a key, turn the small wheel until its arrow (next to its “A”) points at that key’s number on the big wheel. Then for every letter of your message, find it on the big wheel and write down whatever letter lines up with it on the small wheel.

To decode, do the opposite: find each letter of the secret message on the small wheel, and write down whichever letter lines up with it on the big wheel.

For example, lining the arrow up with key 3 puts the small wheel’s “A” next to the big wheel’s “D”. That is the same key 3 shift from the shift table earlier in this activity, just turned into a dial instead of a row of letters.