How does the author see her task? “This book aims to make a significant and original contribution to the existing scholarship on the topic of ancient cryptography by filling a gap in the current literature, and thereby casting new light upon some of the (incorrect) assumptions and (mis)readings of the ancient sources prevalent in the field” (5).
Chapter one tells readers about ancient military structure and communication. One clever inclusion in this chapter involves not so much structure as artisanal chaos: “There are examples of Greeks pretending to be unorganized on purpose to confuse the enemy” (13). Diepenbroek organizes several pieces of military history to demonstrate that the ancient Greeks, while capable of ingenuity and discipline, were also skilled at studied duplicity, what the Greeks called mētis, cunning intelligence.[1] Part of this duplicity was to present the illusion of chaotic behavior to throw off the enemy. Call it diminishing expectations of their own potentiality.
The second chapter examines what is known about secrecy prior to Sparta as well as what was being said about Spartans and secrecy. “No examples of cryptography and steganography known from Egypt and Mesopotamia appear to have had the primary purpose of sending confidential information for strategic purposes” (24). As for Greek sources, Diepenbroek can report that the Iliad includes “an embedded story narrated by the grandson of the mythical hero Bellerophon [in which we learn] that a secret message was once used to arrange a murder” (24). Again, no existing evidence about secrecy in connection with warfare. When it comes to Plato, we do have anxieties in the Phaedrus about writing falling into the wrong hands. Diepenbroek might have pointed instead to Plato’s Seventh Letter, which is explicit about using secrecy to maintain power: “We did not use plain language – it was not safe to do so – but we succeeded by veiled allusions in maintaining the thesis that every man who would preserve himself and the people he rules must follow this course, and that any other will lead to utter destruction” (332d).[2] It seems as if the Spartans knew well this Platonic lesson, and they established what is called the krypteia, a form of “state-sponsored terrorism.”[3] The krypteia was an institution that “promoted, inspired, and enacted violence as a means of power and control.”[4]
Perhaps the most vivid description of what the institution of the krypteia is about comes from Vernant and Pierre Vidal-Naquet[5]:
The young boys had to practice a virtue in silence in the streets, hands hidden behind their cloaks, never glancing to the right or left, but keeping their eyes fixed on the ground. They were never to answer back, never to raise their voices. They were expected to show that, even where modesty was concerned, the male sex was superior to the female. Xenophon reports that they could truly be taken for girls. But in conjunction with this chaste, reserved, as it were hyper-feminine demeanor, they had to do things that were normally forbidden: steal from the adult’s tables, plot and scheme, sneak in and filch food without getting caught. In fierce collective fights in which no holds were barred – biting, scratching, kicking allowed – they were expected to demonstrate the most violent brutality, behave as total savages, attaining the extreme limits of the specifically male virtue known as andreia: the frenzy of the warrior bent on victory at all costs, prepared to devour the enemy’s very heart and brain, the warrior’s face assuming the frightful mask of Gorgo: here, hyper-virility, swinging over into animality, the savagery of the wild beast. (198-199)
This passage’s shocking nature causes some scholars to recoil from its content. Diepenbroek: “The krypteia’s mandate and practices have been debated since Antiquity and must be considered with a large pinch of salt” (38). Rather than engage with this material, Diepenbroek steps aside, because no Spartan sources about the krypteia are available (42). At numerous turns Diepenbroek invokes a cloud of unknowing. “Whether these stories are true, we cannot know” (51); “We cannot know with certainty how much of Plutarch’s and Aulus Gellius’ stories are true” (70); “We can only speculate” (89). Scholars can commend Diepenbroek for her valorization of verification, and simultaneously wonder whether Leo Strauss was right[6] about our need for a different kind of reading in the context of a clandestine society. For instance, one cannot study the Central Intelligence Agency in the same way as one could the Federal Aviation Administration, if only because the CIA isn’t going to keep the same kind of records as the FAA, nor will it expose its records and operations to the public.[7]
Vernant and Vidal-Naquet reconstruct what they can of the krypteia, and for reasons undecipherable to me (isn’t victory at all costs a version of the end justifies the means?), they link the reception of the krypteia to sōphrosunē, an element in the educational training for young men in Sparta. The shocking passage mentioned above is that description of what training in sōphrosunē looked like. The “savagery” Vernant and Vidal-Naquet highlight is put under the category of sōphrosunē, considered a virtue in contemporary classical studies and philosophy. For instance, Joseph Dunne writes about “the virtue of sōphrosunē,”[8] documenting, for instance, how Aristotle linked sōphrosunē and phronesis (277-278). Christopher Moore also calls sōphrosunē a “Greek virtue.”[9] Likewise, Helen North’s foundational study on the topic[10] speaks of the “harmonious product of intense passion under perfect control” (x). North cites Thucydides to confirm that the Spartans regarded sōphrosunē a virtue peculiar to Sparta. What is virtuous in the Vernant and Vidal-Naquet’s passage?
The third chapter, “The Scytale,” includes details about the wide variety of materials that have been called scytale, as well as the kinds of communication that took place using those materials – not just military messages, but love letters. In other instances, scytale means walking stick or baton, and an ancient account has the stick being used as an object to frighten an enemy (52). Yet another ancient author reveals that scytale were used to account for how much money was inside a bag (57). To help clarify how scytale functioned as a cryptographic device, Diepenbroek adds to this section a number of helpful illustrations.
The fourth chapter gives center stage to Aeneas Tacticus’ How to Survive under Siege.” Diepenbroek emphasizes that the focus of How to Survive under Siege “is upon hiding messages to smuggle them in and out of the besieged polis and not upon encoding them to prevent them from being read and understood by hostile agents” (87).
The fifth chapter sizes up the Roman view of the Spartan scytale. The chapter’s content is more about a variety of Roman modes of communication, including having slaves write letters for a free author, or hiding messages in dog collars (108, 112). Diepenbroek wants readers to know about “the Caesar cipher,” a simple letter substitution technique. “It is impossible to trace a continuous line of evolution – or, indeed, any direct relationship – between the Spartan scytale and the development of the Caesar cipher” (119). In fact, the phrase “Caesar cipher” was not used by the Romans, but is a modern appellation.
The sixth and final chapter is an historical overview of ciphers from the Renaissance to the 21st century. Diepenbroek makes a potent case that “it seems naïve for modern historians of cryptography to completely dismiss the ancient Spartan scytale as a ‘toy’ cipher, and to deny its value as a theoretical cryptographic device” (144). In general, her book is devoted to undoing that naïve view. Diepenbroek accomplishes that undoing with aplomb.
Notes
[1] See Marcel Detienne and Jean-Pierre Vernant, Cunning Intelligence in Greek Culture and Society, trans. Janet Lloyd (Sussex, NJ: Humanities Press, 1978).
[2] Translation by Walter Hamilton. Plato: Phaedrus and Letters VII and VIII. London: Penguin Books, 1973.
[3] Brandon D. Ross, “Krypteia: A Form of Ancient Guerrilla Warfare,” Grand Valley Journal of History 1.2 (2012): 1.
[4] Matthew Trundle, “The Spartan Krypteia” in The Topography of Violence in the Greco-Roman World, eds. Garrett G. Fagan and Werner Riess (Ann Arbor: U of Michigan Press, 2016), 60.
[5] Jean-Pierre Vernant and Pierre Vidal-Naquet, Myth and Tragedy in Ancient Greece, trans. Janet Lloyd. (Cambridge: Zone Books, 1990).
[6] Leo Strauss, Persecution and the Art of Writing (Chicago: U of Chicago P, 1988; first published 1952).
[7] An indication of how difficult it is to reconstruct state secrets even in modern times, see Burkhard Bilger’s “The Stasi Files” in the New Yorker (3 June 2024). “Between forty and fifty-five million pages were just torn up, and later stuffed into paper sacks. Finishing the job [of piecing together the torn pages of Stasi files] will take more than six hundred years” (41).
[8] Joseph Dunne, Back to the Rough Ground: Practical Judgment and the Lure of Technique (Notre Dame: U of Notre Dame P, 1993), p. 277.
[9] Christopher Moore, The Virtue of Agency: Sōphrosunē and Self-Constitution in Classical Greece (Oxford: Oxford UP, 2023), p. 1. Moore offers a broad definition: “Sōphrosunē is the capacity to act well in the face of a distinctive human challenge” (2). Is hunting and murdering helots “a distinctive human challenge”? Trundle expresses his frustration with those who want to find virtue where violence is mentioned: “Despite all the denial of some modern commentators regarding the extreme activities of the krypteia, there can be little doubt that ancient elites exploited the weak and maintained their power without pity; the loss of one or two [helots] did not affect any single Spartan master economically.”
[10] Helen North, Sophrosyne: Self-Knowledge and Self-Restraint in Greek Literature (Ithaca: Cornell UP, 1966).