Rotate the discs to select a cipher key, or use the slider "key" variable to select between 0 to 26. Click Encrypt or Decrypt buttons to perform a Caesar cipher encoding or decoding of whatever message you type in. If no message is typed, the previous output will be the input. See the message get transcoded in real time, and use the speed slider to select how fast this happens. Operations will be done at 4/speed seconds per letter. Zero means as fast as possible. The inside disk is the "plain text" so when encrypting the input letters will be looked on it. The outside disk is the "cipher text disc" so when decrypting the input letters will be looked up on it.
Caesar cipher is a common substitution cipher which is usually taught as an example of an insecure cryptosystem. Still, this is still a useful and fun concept to teach children about encoding and decoding algorithms, as it is for example done by the Unplugged CS and CS First With Google curricula. This game can be used to show students how the process they perform by hand can also be done at a much higher speed with the computer. They can play by writing encrypted messages by hand and decoding it on the computer or vice-versa, or passing encrypted messages to other classmates. They can also use it to learn how to perform simple cryptanalysis, either by doing statistical analysis (finding the most frequent letters/words), trying to guess words or even bruteforcing the 25 possible keys.
