Ancient Cybersecurity? Deciphering the Spartan Scytale

Martine Diepenbroek

When Pharnabazus [the Persian statesman] was outraged by Lysander pillaging and wasting his territory, he sent men to Sparta to denounce him… The ephors [senior magistrates] were incensed, and when they found Thorax, one of Lysander’s friends and fellow-generals, with money in his private possession, they put him to death, and sent a scytale to Lysander, ordering him home… When the scytale reached him at the Hellespont, Lysander was much disturbed.              

(Plutarch, Life of Lysander, 19-20)

 

Communication security is of integral importance to our modern world: when security is breached, the consequences are often of global importance. Yet these problems are not the invention of the computer age: since antiquity, individuals in all civilisations have been trying to use technology to encipher confidential correspondence, while others have been desperately trying to decipher it.

The Ancient Greeks, and in turn the Romans, seem to have been experts in the art of cryptography (“hidden-writing”). One particularly interesting example of ancient cryptography can be found in 5^th– and 4^th-century BC Sparta. According to our sources, the ephors – leading magistrates who shared power with the two kings^[1]For more on this complicated set-up, see Marshall Sahlins, “Twin-born with greatness: the dual kingship of Sparta,” Journal of Ethnographic Theory 1 (2011) 63–101; also of interest is Ellen Millender’s “Spartan Literacy Revisited” (Classical Antiquity 20 (2001), 121–64). Our primary ancient sources are Xenophon’s Hellenica 3.3, and the anonymous Constitution of Sparta 15. – used a scytale (a “stick” or “staff”) to communicate with commanders in the field on confidential matters.

In the episode that introduces this piece, Plutarch^[2]Life of Lysander 19.4. describes how the Persian statesman Pharnabazus complained to the Spartan ephors that their general Lysander was pillaging his territories for no purpose. Therefore the ephors sent a confidential – and most probably encrypted – message by scytale to Lysander summoning him to come home – or be sentenced to death on account of this misbehaviour. The fact that Lysander was much disturbed shows that the message was both powerful and important. So what exactly was a scytale and how was it used?

The scytale could have been used for a variety of purposes, including as a messenger authentication stick, as a sort of military name-tag, and as a cryptographic device. From Plutarch we know that scytalae were very probably used as tools for cryptography during wartime. In his Parallel Lives we find various Spartans who successfully sent and received secret scytale-messages in this context, including the Spartan military leaders Lysander, Clearchus and Agesilaus.^[3]To sketch some biographical details: Lysander was a Spartan admiral who commanded the fleet that defeated the Athenians at Aegospotami in the Hellespont in 405 BC; Clearchus led the Peloponnesian delegation of the Army of the Ten Thousand in a battle between Cyrus and his brother Artaxerxes, in which the Greeks aided Cyrus (401 BC); Agesilaus was a king of Sparta and the main actor during the period of Spartan hegemony that followed the Peloponnesian War (431–404 BC). All three leaders were most likely to have sent and received scytale-messages.

Two complete descriptions of the use of the scytale as a cryptographic device can be found in Plutarch (Lysander 19.5–7) and Aulus Gellius (Attic Nights 17.9.6–16). Both authors were active in the 2^nd century AD, so were writing at some considerable distance from the period in which scytalae were used, i.e. in the 5^th and 4^th centuries BC, and especially the period between the outbreak of the Peloponnesian War in 431 and the Battle of Leuctra in 371. Nevertheless, both Plutarch and Gellius offer useful accounts of the working of this deceptively simple device.

According to the authors, before an admiral or a general was sent to war, he was given a scytale to communicate with the ephors in Sparta. Whenever either party wanted to send an important confidential message to the other, they would take a thin strip of leather parchment and wind it round their scytale, thereby making sure that every bit of the stick was covered in parchment. Plutarch used the word βιβλίον (biblion, literally “little book”, and the word that gives us “Bible”) to describe this writing material and its text: he adds that it was “like a long and narrow leather strap” (Lysander 19.5). Aulus Gellius also believed it to have been a strip of parchment, for which he used the Latin word lorum (Attic Nights 17.9.9).

After wrapping the strip around the scytale, the sender would write whatever they wished to communicate on the parchment. When they had written the message, they would unwrap the strip from the scytale and send just that strip to the intended recipient. But by unwrapping the text strip from the scytale, all letters in the original message were transposed to a different position. So, according to Plutarch, when a general in the field received a scytale message, he could not have gotten any meaning from it, since the letters would have been hopelessly disarranged (Lysander 19.7). Gellius additionally mentioned that in a scytale-message one had to deal with many partial and broken letters. The unrolling of the strip would have made the letters imperfect, with their various parts and strokes seeming haphazardly separated.

To reconstruct the intended message, the recipient had to rewrap the strip around his own matching scytale. For the method to work well, both scytalae had to be exactly the same size and diameter, and the strip had to be rewrapped around the second scytale just as loosely or as tightly as it had been done the first time. Otherwise, the letters would not have returned to their original place. This changing of the letters’ placement is known as ‘transposition’ in modern cryptography. This transposing of letters makes the scytale-method the first transposition cipher known in history – at least theoretically, since there is no surviving physical evidence of the process in action.

The following example shows how the transposition encryption would have worked – according to Plutarch’s and Gellius’ descriptions – and how the strip of writing material may have looked during the subsequent steps in the process. For this example the text ‘Enemy attacks at Dawn Tomorrow’ will be used.

First, a strip of writing material was wrapped around a scytale to create small near-rectangular columns. Since the wrapping was done by hand, it is highly likely that the edges of the strip overlapped each other. Therefore, the columns are not all exactly the same size:

Then the text would have been written on the strip of writing material. In the next two images, the text is written from left to right and top to bottom on two lines:

Plutarch described in his account that all letters of a message were rearranged once the strip of writing material has been unwrapped from the scytale.^[4]Lysander 19.7. By unwrapping the strip, the letters now appear per column, instead of per row. So, instead of reading E-N-E-M-Y, the first word of the message, one now reads E-D-N-A-E et cetera. In the image below, every letter of the message has been written on a complete piece of material strip. In other words, no letters were written over the edges of the strip, meaning that when the strip was subsequently removed from the scytale, all letters would have remained intact, having simply been rearranged in sequence.

However, according to Plutarch, the complete scytale was covered in the writing material. This makes it more plausible that the sender of a message did not in practice write with all letters neatly contained within complete pieces of the scytale’s material strip, but that they also ran across the edges of the strip:

If the message was written in this form, some letters would have been written whole on a complete piece of strip, whereas others would have straddled the strip’s edges and become broken when it was unwrapped from the scytale. Aulus Gellius confirms that this is what happened in practice.^[5]Attic Nights 17.9.12–14. If the strip from Figure 3 – for example – was unwrapped from the scytale, the strip would look like the following diagram, in which the strip is cut into pieces to show the difference between partial and complete letters:

We can see just how challenging it would have been to attempt to reconstruct the original text from this scrambled ciphertext. It would certainly not be impossible, but – without a scytale rod of the same size as the one used in the original encryption – would have been incredibly time-consuming. A good modern parallel might be the paper shredder, which offers one way of ‘encrypting’ or scrambling a confidential source text. With patience, skill, and time, the original text can be reconstructed from the shredded strips of paper. The advantage of the scytale device, however, is that it offers the opportunity for that reconstruction to be managed much more quickly and easily by those with the right tool.

Greek sources vary in their discussions of the scytale and only sometimes associate it with secret messaging.^[6]Since it literally means “stick”, the word seems also to have referred to a simple staff or baton, a walking stick, a ‘dispatch stick’, sticks used for marking and record-keeping, and even – at least once – a phallus. The clearest descriptions of the scytale as a cryptographic device are found in the two authors mentioned here: Plutarch and Aulus Gellius. Although they do not prove definitively that scytalae were used in practice for secret communication, the ingenious rearrangement of letters they describe makes scytalae a likely candidate for the earliest known theoretical transposition cipher in history. The Spartans have not had much effect on the development of world technology but, in the cutting-edge science of cryptography, they might just have been its inventive genius.

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Martine Diepenbroek is a Dutch Ancient Historian who has recently completed a PhD in Classics and Ancient History at the University of Bristol. Her research focuses on ancient cryptography – especially on the Spartan scytale. She has previously published in KLEOS (The Amsterdam Bulletin of Ancient Studies and Archaeology) and in Ancient Warfare Magazine. She is currently in the process of publishing her PhD thesis with Bloomsbury (London).

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Further Reading

Those in search for further detail about the scytale may enjoy two pieces by Thomas Kelly: “The Spartan Scytale,” in J. W. Eadie, & J. Ober (eds.) The Craft of the Ancient Historian: Essays in Honor of Chester G. Starr (University Press of America, Lanham, MD) 141–69, and “The Myth of the Skytale,” Cryptologia 22 (1998) 253–60. Also if interest is Stephanie West’s “Archilochus’ Message Stick,” Classical Quarterly 38 (1998) 42–8.