My dad taught me this cipher when I was a kid, and I've wanted for a long time to make a printable code wheel that would allow others to learn the cipher. This is some sort of variant on the Vigenere cipher (http://en.wikipedia.org/wiki/Vigenere_cipher) but I'm not sure of the actual name of this variant, so if anybody knows, please let me know in the comments! I know it is also related to the key autokey and Alberti ciphers.
In addition, I have a prize for the first person to correctly decrypt the ciphertext below and post the plaintext to the comments... I loved the steganography challenge in the Seej block, and it's high time we had another contest... Good luck!
Oh, and you will find that brute force is not the way to go... there are 1.243841e 142 possible keys. :)
UPDATE: There is now a monocase alphas only ciphertext of the same plaintext, which reduces your keyspace down to 4.0329146e 26 possible keys.
Keep in mind that an attacker doesn't need to do an exhaustive search of all of these keys; once he has some of the letters right, they will help him get more letters right, and the effect will snowball until he has the entire key. Indeed, I cracked the alphas only version by hand in less than 2 hours.
This algorithm should therefore not be used for anything that you actually need to keep secret.
[ALPHAS ONLY CIPHERTEXT]
[END ALPHAS ONLY CIPHERTEXT]
1: Print it out.
2: Put it together.
3: Follow the instructions on the webpage download. If you want, you can also use this wheel to perform simple Caesar ciphers.
4: Optional: Use the .SCAD file to print two copies of a new key, and give one to a friend. Now you can communicate securely with that friend!
5: If you'd like to participate in the contest, you will want to download the python version of the cipher.