This is how to make a homemade Cipher Device for fun by recycling used or damaged cds. I did this fast but you can get more creative and make it a bit more complex or even more durable using stickers and other materials found at home.

Step 1: Materials

First find cds you dont need or that don't work. One large one small.
 This is awkward! I was gonna make something like that with no knowledge whatsoever it already existed...
Great idea just what I was looking for, my grandson is 8 and I am sure we will have some learning going on with the fun, plus grandma here has an idea for some grown-ups too. Will be referring others to check it out.
It's also very nice to use with the Vigenere cipher! It's based on the Caesar cipher but depending on the size of the key, it may be nearly impossible to crack!<br/>Take a look at the <a rel="nofollow" href="http://en.wikipedia.org/wiki/Vigenere_cipher">Vigenere cipher</a><br/>
i made something like this some day long long ago in a galaxy far far away, but it was for guitar chords and such. insteada of a smaller cd (becuase i couldnt find one) i just used those clear cd things that come in the pack. it was pretty cool, but i think this one mihgt be better becuase ...i dont know :-) <3 king alvincredible, the benevolent chipmunk ruler of the third realm of gondor.
FOR GONDOR!!!!!!!!!!!!!!
I don't think I would ever get around to using it, but it looks cool! Reminds me of the cryptex from DaVinci Code.
When I saw the pic in the Make blog, my mind raced: "How did they cut the CD into an inner and outer ring that could nest so beautifully? They must have used two CDs, one to make the smaller, and one to make the outer, but still, cutting those things is no easy task. I bet they used a mill. Or a lathe!" That would be pretty cool. I was picturing other homebrew methods, with CDs clamped onto drills, mounted to tables, holding X-actos just so, fake-lathing away the outer part of the inner disc, and the inner part of the outer disc. Then I see it's a large and small CD. Haha! I have a box of like 200 of those mini CDs, too, which are always too small by usually ~10MB to ever be useful. I love how it never even occurred to me to just use one of those as the smaller wheel. When will I learn to just KISS? Well done - thanks for sharing.
Wow, i like that alot, really slick and clean. Nice job!
Thanks for the comments. It's really just a cheap but easy to make Cipher Device similar to the Pletts Device. There are many ways to make it fancier or more complex. Maybe adding a way to spin it randomly or cutting out a notch on the outside of the dvd case to expose the letters selected.
This is a weak encryption, called the "Caesar shift cypher", if you simply use an offset of, say, lining A up with E. If you want more (still not much) security, you can write the letters in a random order, then make a second wheel that is identical. For the best security (short of getting another wheel or changing the design) you should randomise the alphabet, then change where the A is after each letter is encoded. Use a common rule, then you will be able to encrypt and decrypt in sync. One possible rule is, start with the A over the 5th letter, then advance CW by 5 each time while encrypting. If the decoder repeats this they will be able to decode it. A better variant could use the message itself to change the encryption. Advance CW by the position of the letter encrypted each time. To decrypt, tell the person the last letter used, and then they advance CCW as they go, starting from the other end of the transmission.
what does it do?
By rotating the inner wheel to match up with the outer wheel in various ways, you can substitute letter/numbers from the inner wheel for the letter on the outer wheel. In the last picture shown, for example, you could show a letter 'G' as either '8' or 'H'. I agree with matthewtoldme, however, randomizing the letter order on the inner/outer wheel would make for a more useful cipher than simply shifting.
This is basically a decoder ring. Cool idea.<br/><br/><a rel="nofollow" href="http://www.exploratorium.edu/ronh/secret/secret.html">http://www.exploratorium.edu/ronh/secret/secret.html</a><br/><a rel="nofollow" href="http://en.wikipedia.org/wiki/Secret_decoder_ring">http://en.wikipedia.org/wiki/Secret_decoder_ring</a><br/>
writing either the outer or the inner characters in a randomized order might be helpful

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