Breakthrough in renaissance cryptography: A book review

Cryptologia, Jan 1999 by Reeds, Jim

ADDRESS: AT&T Labs - Research, Florham Park, New Jersey 07932 USA. Email: reeds(R)research.att.com.

Thomas Ernst, Schwarzweisse Magie: Der Schlussel zum dritten Buch der Steganographia des Trithemius. A monograph filling an entire issue of the journal Daphnis: Zeitschrift fur Mittlere Deutsche Literatur 25, no. 1 (1996): 1-205. Separate copies of this issue of Daphnis are sold by the publisher as if it were a book, ISBN 90-5183-9855-5. $34.00. Publisher's address: Editions Rodopi B. V., Kaizersgracht 302-304, NL 1016 EX Amsterdam, The Netherlands.

Ernst's paper (whose title can be translated as "Magic in black and white: the key to Book 3 of Trithemius's Steganographia" ) continues the long scholarly debate about whether Trithemius's Steganographia (written ca. 1500 but first printed 1606) was primarily a demonology book or a cryptography book; recent contributions to this debate being (on the demonology side) D. P. Walker's influential book Spiritual and Demonic Magic from Ficino to Campanella, (London: Warburg Institute, 1958) and (on the cryptography side) Wayne Shumaker Renaissance Curiosa: John Dee's conversations with angles, Girolamo Cardano's horoscope of Christ, Johannes Trithemius and cryptography. George Dalgarno 's Universal language, Medieval and Renaissance Texts and Studies, 8 (Binghamton, New York: Center for Medieval and Early Renaissance Studies, 1982). Ernst's contribution should settle the matter once and for all, conclusively proving that the Steganographia was really a cryptography book disguised as a magic book, but apparently it will take a while before the message sinks in, as evidenced by Noel Brann's Trithemius and Magical Theology: A chapter in the controversy over occult studies in early modern Europe (Albany, New York: State University of New York Press, 1998), which cites but does not believe Ernst.

The situation before Ernst was roughly as sketched in Chapter 4 of Kahn's The Codebreakers (New York: Macmillan, 1967). All three books of Trithemius's Steganographia are ostensibly about magic, sending and receiving messages with the aid of spirits, demon conjuration, and so on. But in fact in Books 1 and 2 this is just an elaborate disguise for Trithemius's use of what is nowadays called steganography to conceal plain text messages (in Book 1) and monoalphabetic cipher texts (in Book 2), as has been known (in the cryptographic literature at least) for about 400 years. Walker contended that Book 3 was different: there were no hidden cryptograms buried within its text, and Book 3 reflects Trithemius's true magical intent. Shumaker demurred, arguing that there might be cryptograms hidden there, in which case the demonological text of Book 3 would be just more cover text like that of Books 1 and 2. Shumaker's cryptographic skill, however, was not up to the task of finding such cryptograms, and main-stream historians have on the whole not believed his speculations.

But Ernst has identified and solved these "missing" cryptograms. All the numerical data in Book 3 that Trithemius passes off as astrological turns out to be numerical cipher text, which Ernst handily breaks. The plain texts are similar to those of Books 1 and 2: "spy-story" sentences like "The bringer of this message is a rogue and a thief, guard yourself for he plans you ill" and "Gaza frequens Libicos duxit Carthago triumphos," a Latin equivalent of the "The quick brown fox ... "

Further, Ernst accomplishes something no one else had attempted, namely explaining two other books published together with the Steganographia: the Clavis steganographiae and the Clavis generalis, meaning Steganography key and General key, respectively. The first of these contains a fairly close explanation of how the concealment ciphers of Books 1 and 2 work, the second gives a very brief general explanation of several cryptographic techniques, including those used in Books 1 and 2. Everyone, I think, assumed they were ex post facto explanations, written by Trithemius or a confidant, appended to the end of the Steganographia. But Ernst shows that they represent two stages of drafts of the Steganographia. The older Clavis generalis, simply states cryptographic techniques. Then the Clavis steganographiae is embellished with examples, stretching its length considerably, especially because of the way Trithemius's concealment cipher works. Finally, a layer of obfuscatory demonological patter is laid down, resulting in the controversial Steganographia.

What's at stake is more than just the reputation of one Renaissance cryptography author. There are currently two linked problems in the study of the history of 16th century cryptography: What caused the immense outpouring of new books on the subject, written by people who were typically not even part-time professional cryptographers, introducing a wealth of new techniques which did not in fact receive much practical use until centuries later but which none the less were the seed ideas on which even 20th century developments were based? In other words, why were the 16th century cryptography authors interested in the field? And secondly, what relationship, if any, existed between the new 16th century interest in cryptography and its growing interest in the occult arts: Hermeticism, and the Kabbalah? If, as Umberto Eco suggests in his The search for the perfect language, trans. James Fentress (Oxford: Blackwell, 1995) - as Kahn indirectly does in his paper "On the origin of polyalphabetic substitution" Isis 71 (1980), 122-127 - techniques of Renaissance cryptography are simple by-products or applications of the Kabbalistic letter combinatory operations of tseruf and gematria, the question still remains, transmuted into: why did Renaissance Kabbalists see the desirability of inventing a new cryptography?