What is a scytale, and how was it used for encryption in antiquity?

A scytale is an ancient Spartan encryption device — a strip of parchment wound around a rod of specific diameter.

Dating to around 500 BC, it's one of the earliest known encryption tools:

1. A strip of parchment (or leather) is wound tightly around a rod
2. The message is written across the wrapped strip
3. When unwound, the letters appear scrambled
4. Only someone with a rod of the exact same diameter can read the message

This is a transposition cipher — the letters of the message are rearranged, but not substituted.

Tip: The scytale's "key" is the diameter of the rod. This makes it easy to break — there are only so many possible diameters to try.