The Spartan rod: write along the rod, unwind the strip and read it turn by turn; decryption winds it back.
Procedure
How it works
The scytale is described in Greek sources as a tool of Spartan commanders: a strip of leather or parchment wound around a rod of agreed thickness, with the message written along the rod. Unwound, the strip shows a jumble of letters; wound around a rod of the same thickness, the message reappears.
If one turn of the strip holds $d$ letters, the message is written in $d$ rows along the rod, each $\lceil n / d \rceil$ letters long, and the strip carries the letters column by column. So the scytale is a columnar transposition with the columns read in their natural order.
The only key is the thickness of the rod. Trying every value of $d$ breaks it at once, so the scytale was a way of writing more than a cipher.
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