The scytale (also skytale) may be the earliest encryption device in recorded history. Several web resources credit the Greek historian Thucydides and biographer Plutarch with the earliest recordings describing a scytale.
Basically, a scytale was a wooden cylinder around which a strip of paper, fabric or leather was wound. The message was written lengthwise along the strip and then unwound. Several instances have described the strip as a piece of leather worn by a soldier as a belt to the delivery destination. The belt was then wrapped around another scytale of equal diameter for translation.
Making such a device at home is simple, and great rainy day activity for kids. What do you need? To start, some writing device to compose the message, some fabric or strips of paper, some tape and single cylinder (or a pair of cylinders). For a cylinder, a pencil will suffice, but something a bit larger in diameter, like a broom handle or soda bottle might be easier to work with. Also, I've found that long strips of paper (like from the edge of a newspaper page) are more fun, as are longer cylinders (like broom handles or dowel rods).
Secure the end of the strip to the rod, and wind it around the cylinder along the length. Write your message, one or two letters per strip width along the length of the cylinder, leaving spaces between words (or not!). Continue down the length, rotating to start a new row as needed.
I wrapped a length of news paper around a plastic water bottle. Where the strip began and ended, it circled the bottle three times, but in other places, it only wrapped around twice. I wrote my message and then removed the strip. From top to bottom (with a "#" to represent a space, it read:
I M U E L R A I G A B O # Y T D W L I M # # # R N Y E D N # # O K B # A # I L A S # A C R T
Which, when wrapped around a bottle of correct diameter reads:
I AM CURRENTLY READING A BOOK BY TAD WILLIAMS
This method can implemented in many ways, by combining different color combinations, skipping letters, substitutions, writing on both sides of the strip, etc. The links below are to articles about the history of the scytale and pictures of home made scytales.
more ... could be something a Latin teacher might do in class.