Secret Decoder Rings

Alberti Cipher Disk
by Augusto Buonafalce contributed by Antonio G Colombo
(Alterations: size and transparency changed)
Licensed under CC BY-SA 3.0

Whatever happened to secret decoder rings?

Back when I was a kid in the dark ages, we all had secret decoder rings. Okay. Not everybody had them. After all, if they did, we could never send secret messages to our friends who had those secret decoder rings. Everybody would be in on the secrets. But we did have them. We might have even used them...