Parker, Parageographer and Professor of Classics at the University of Texas, writes in a note to his 1964 translation of the Lysistrata, on page 121 of the paperback edition:
"...a *skytale*, a tapered rod which was Sparta's contribution cryptography. A strip of leather was wound about the rod, inscribed with the message, and unwound for transmission. A messenger then delivered the strip to the qualified recipient, who deciphered it by winding it around a rod uniform in size and shape with the first. Any interceptor found a meaningless string of letters."
If I correctly recall my conversations with Professor Parker on the matter of this code-stick, the device is pronounced something like SCOO-TA-LA.
In the Lysistrata, the women of Sparta and Athens conspire to deny their husbands sex until the two cities end their ongoing war. The men, therefore, wander around with hard- ons the whole time. The code-stick appears in Aristophanes's comedy in the following scene between an Athenian commissioner and a Spartan messenger: (From page 92 of Parker's Translation)
[Throwing open the Spartan's cloak, exposing the phallus.]
You clown, you've got an erection!
Hain't got no sech a thang! You stop this-hyer
What *have* you got there, then?
Thet-thur's a Spartan *e*pistle. In code.
I have the key.
[Throwing open his cloak.]
Behold another Spartan *e*pistle. In code.